Qualitative analysis of lead content in biological material. Fractional analysis of metals and prospects for its application in forensic chemistry. Study of mineralizates for the presence of lead

Municipal budgetary educational institution

"Ryzhkovskaya Secondary School"

Kardymovsky district, Smolensk region

Competition for students of general education organizations

and additional education organizations in the Smolensk region

for the best environmental project “We live in the Smolensk region”

Ecological project

“Comprehensive analysis of the content of heavy metal compounds

in the environment and their impact on organisms"

Biryukova Alina Alexandrovna

Grade: 9

FULL NAME. work manager:

Baranova Olga Alekseevna

Titkovo village

2017

Table of contents

Introduction………………………………………………………………………………….………3

Chapter I . Heavy metals……………………………………………………………….…….. 5

Chapter II . Sources of heavy metal compounds entering the environment and living organisms…………….………………………………………………………………………………..…7

2.1. The entry of heavy metal compounds into the soil………………………..………..8

2.2. Intake of heavy metal compounds into water bodies………………………………9

2.3. Release of heavy metal compounds into the atmosphere…………………………….…9

2.4. Intake of heavy metal compounds into living organisms……………………10

Chapter III . Determination of the presence of heavy metal compounds in the environment and their impact on living organisms…………………………………………………….12

3.1. Compounds of heavy metals in soil …………………………………………13

3.1.1. Methodology for determining the presence of heavy metal compounds in soil......13

3.1.2. Results of analysis of the content of heavy metal compounds in soil……..…14

3.2. Compounds of heavy metals in natural waters………………………….………...14

3.2.1. Methodology for determining the presence of heavy metal compounds in natural waters…………………………………………………………………………………..14

3.2.2. Results of analysis of the content of heavy metal compounds in natural waters…………………………………………………………………………………………....14

3.3. Compounds of heavy metals in the atmosphere………………………………………………………15

3.3.1. Methodology for determining the presence of heavy metal compounds in the atmosphere ………………………………………………………………………………………..15

3.3.2. Results of analysis of the content of heavy metal compounds in the atmosphere…………………………………………………………………………………………...16

3.4. Heavy metal compounds and living organisms………………………………………………………17

3.4.1. Methodology for determining the effects of heavy metal compounds on organisms…………………………………………………………………………………………...17

3.4.2. Results of determining the impact of heavy metal compounds on living organisms…………………………………………………………………………………18

Conclusion……………………………………………………...……………………………..20

References………………………………………………………………………………………..…..21

Appendix ……………………………………………………………..……………………….22

Introduction

The environment is the habitat of living organisms that are in contact with it throughout their lives. Organisms receive from the environment everything they need for normal life: oxygen for breathing, water, nutrients, microelements and much more. Among the chemical elements entering organisms, heavy metals in the form of ions occupy a special place.

It has been established that heavy metal ions are normally present in the environment due to their intake from natural compounds, but their natural content is extremely low. Recently, the human impact on the environment has been increasing, and now the source of heavy metal compounds is also human activity (metallurgical production, motor vehicles, fertilizers), and the number of heavy metal ions of anthropogenic origin in the environment is increasing every year. Consequently, these ions will enter the organisms in larger quantities.

Does the “more is better” rule apply here? Everyone knows that living organisms contain metals, including heavy ones: for example, iron in hemoglobin, zinc in insulin and many enzymes, copper is needed for the formation of nervous tissue and in the processes of hematopoiesis, and molybdenum activates the processes of binding atmospheric nitrogen by nodule bacteria. But these and many other chemical elements - heavy metals - are required by living organisms for normal functioning in rather small quantities, while some of the heavy metals, even in trace quantities, have a toxic effect, being the strongest toxic metals (mercury, lead, cadmium).

Is human activity really a powerful source of heavy metal compounds entering the environment, and do heavy metals themselves negatively affect living organisms? The work is devoted to the study of these issues.

At the beginning of the work it was put forwardhypothesis: heavy metal compounds are present in the environment of the study area (rural area), the content of heavy metal compounds is higher, the closer the sampling area is to the road; heavy metal compounds have a depressing effect on living organisms.

Target: studying the content of heavy metal compounds in the environment (air, soil, water) and their impact on living organisms.

To achieve this goal it is necessary to decidetasks :

Study the scientific literature on this issue.

Study methods for determining heavy metal compounds in the environment.

Conduct a qualitative analysis of soil, snow, water, biological material (lichens) samples for the content of heavy metal compounds.

Determine the impact of heavy metal compounds on living organisms.

Assess the degree of environmental pollution with heavy metal compounds in the study area.

Object of study : pollution of the environment and living organisms with heavy metal compounds.

Subject of study : soil, snow, water, living organisms (lichens, watercress).

Research methods:

Theoretical method

Morphometric method

Experimental method

Organoleptic method

Mathematical method

Location of the study: Titkovo village, Kardymovsky district.

Time frame for the study: February-March 2017.

Chapter I . Heavy metals

Heavy metals are a group of chemical elements with the properties of metals and a significant atomic weight, more than 40. About forty different definitions of the term heavy metals are known, and it is impossible to point to one of them as the most accepted. Accordingly, the list of heavy metals according to different definitions will include different elements.

The term “heavy metals” is most often considered not from a chemical, but from a medical and environmental point of view. Thus, when included in this category, not only the chemical and physical properties of an element are taken into account, but also its biological activity and toxicity, as well as the volume of use in economic activities.

In works devoted to the problems of environmental pollution and environmental monitoring, todayheavy metals include more than 40 metals of the periodic table D.I. Mendeleev with an atomic mass of over 50 atomic units:V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, Sn, Hg, Pb, Bi etc. At the same time, the following conditions play an important role in the categorization of heavy metals: their high toxicity to living organisms in relatively low concentrations, as well as the ability to bioaccumulate and biomagnify. Almost all metals that fall under this definition (with the exception of lead, mercury, cadmium and bismuth, the biological role of which is currently unclear) are actively involved in biological processes and are part of many enzymes. According to the classification of N. Reimers, metals with a density of more than 8 g/cm should be considered heavy 3 . Thus, heavy metals includePb, Cu, Zn, Ni, Cd, Co, Sb, Sn, Bi, Hg .

Manyheavy metals , such as , , , , participate in biological processes and in certain quantities are necessary for the functioning of plants, animals and humans . On the other side,heavy metals and their compounds may have harmful effects on living organisms. Moreover, the negative impact of heavy metals on living organisms and human health is manifested not only in the direct effects of high concentrations, but also in long-term consequences associated with their cumulative effect. Heavy metal compounds cause a number of diseases and general inhibition of vital processes. Metals that have no useful role in biological processes, such as And , are defined astoxic metals . In particularlead, which classified as highly hazardous substances along with arsenic, cadmium, mercury, selenium, zinc, fluorine and benzaprene (GOST 3778-98).Some elements such as or , which usually have toxic effects on living organisms, may be beneficial for some species.

Chapter II . Sources of heavy metal compounds

into the environment and living organisms

Among the biosphere pollutants that are of greatest interest to various quality control services, metals (primarily heavy, that is, having an atomic weight of more than 40) are among the most important. This is largely due to the biological activity of many of them.

Sources of heavy metals are divided into natural (weathering of rocks and minerals, erosion processes, volcanic activity) and man-made (mining and processing of minerals, fuel combustion, traffic, agricultural activities). Some of the man-made emissions entering the natural environment in the form of fine aerosols are transported over significant distances and cause global pollution. The other part enters drainless reservoirs, where heavy metals accumulate and become a source of secondary pollution, i.e. the formation of dangerous pollutants during physical and chemical processes occurring directly in the environment (for example, the formation of poisonous phosgene gas from non-toxic substances). Heavy metals accumulate in the soil, especially in the upper humus horizons, and are slowly removed by leaching, consumption by plants, erosion and deflation - blowing out of soils.

The period of half-removal or removal of half of the initial concentration is a long time: for zinc - from 70 to 510 years, for cadmium - from 13 to 110 years, for copper - from 310 to 1500 years and for lead - from 740 to 5900 years. In the humus part of the soil, the primary transformation of the compounds found in it occurs.

Heavy metals have a high ability for a variety of chemical, physicochemical and biological reactions. Many of them have variable valency and participate in redox processes. Heavy metals and their compounds, like other chemical compounds, are capable of moving and being redistributed in living environments, i.e. migrate. The migration of heavy metal compounds occurs largely in the form of an organomineral component.

Possible sources of pollution of the biosphere with heavy metals of technogenic origin include enterprises of ferrous and non-ferrous metallurgy (aerosol emissions polluting the atmosphere, industrial effluents polluting surface waters), mechanical engineering (plating baths of copper plating, nickel plating, chrome plating, cadmium plating), factoriesfor recycling batteries, automobile transport.

In addition to anthropogenic sources of environmental pollution with heavy metals, there are other natural sources, such as volcanic eruptions: cadmium was discovered relatively recently in the products of the eruption of Mount Etna on the island of Sicily in the Mediterranean Sea. Increased concentrations of toxic metals in the surface waters of some lakes may occur as a result of acid rain, which leads to the dissolution of minerals and rocks washed by these lakes. All these sources of pollution cause an increase in the content of metal pollutants in the biosphere or its components (air, water, soil, living organisms) compared to the natural, so-called background level.

2.1. The entry of heavy metal compounds into the soil

Soil is the main medium into which heavy metals enter, including from the atmospherewith emissions from industrial enterprises, and lead - from vehicle exhaust gases. Heavy metals most often enter the soil from the atmosphere in the form of oxides, where they gradually dissolve, turning into hydroxides, carbonates or into the form of exchangeable cations. Soil withIt is a source of secondary pollution of surface air and waters that flow from it into the World Ocean. From the soil, heavy metals are absorbed by plants, which then become food for more highly organized animals.

The duration of residence of polluting components in the soil is much higher than in other parts of the biosphere, which leads to changes in the composition and properties of the soil as a dynamic system and ultimately causes an imbalance in ecological processes.

Under normal natural conditions, all processes occurring in soils are in balance. Changes in the composition and properties of the soil can be caused by natural phenomena, but most often humans are to blame for disturbing the equilibrium state of the soil:

atmospheric transport of pollutants in the form of aerosols and dust (heavy metals);

non-terrestrial pollution - dumps of large-scale industries and emissions from fuel and energy complexes;

plant litter. Toxic elements in any state are absorbed by the leaves or deposited on the leaf surface. Then, when the leaves fall, these compounds enter the soil .

The determination of heavy metals is primarily carried out in soils located in areas of environmental disaster, on agricultural lands adjacent to soil pollutants with heavy metals, and in fields intended for growing environmentally friendly products.

If soils are contaminated with heavy metals and radionuclides, it is almost impossible to clean them. So far, the only way is known: to sow such soils with fast-growing crops that produce large phytomass. Such crops that extract heavy metals must be destroyed after ripening. It takes decades to restore contaminated soils.

2.2. The entry of heavy metal compounds into water bodies

Metal ions are essential components of natural bodies of water. Depending on environmental conditions (pH, redox potential), they exist in different oxidation states and are part of a variety of inorganic and organometallic compounds. Many metals form fairly strong complexes with organic matter; These complexes are one of the most important forms of migration of elements in natural waters.

Heavy metals as microelements are constantly found in natural reservoirs and the organs of aquatic organisms. Depending on geochemical conditions, wide fluctuations in their level are observed.

At the same time, heavy metals and their salts are widespread industrial pollutants. They enter reservoirs both from natural sources (rocks, surface layers of soil and groundwater), and from wastewater from many industrial enterprises and atmospheric precipitation, which are polluted by smoke emissions. For example, natural sources of lead entering surface waters are the dissolution processes of endogenous (galena) and exogenous (anglesite, cerussite, etc.) minerals. A significant increase in the content of lead in the environment (including in surface waters) is associated with the combustion of coal, the use of tetraethyl lead as an anti-knock agent in motor fuel, and the discharge into water bodies with wastewater from ore processing factories, some metallurgical plants, chemical plants, mines, etc.

2.3. Release of heavy metal compounds into the atmosphere

Road transport that runs on liquid fuel (gasoline, diesel fuel and kerosene), combined heat and power plants (CHP) and combined heat and power plants (CHP) are one of the main sources of air pollution. Car exhaust emissions contain heavy metals, including lead.Higher concentrations of lead in the atmospheric air of cities with large industrial enterprises.

Intake of heavy metals into the atmosphere, % of the amount

Source

Heavy metal

Сd

Common natural source

26,3

29,0

4,5

81,0

Anthropogenic source

73,7

71,0

95,5

19,0

2.4. The entry of heavy metal compounds into living organisms

Plant foods are the main source of heavy metals in the body of humans and animals. According to data, 40–80% of heavy metals come from it, and only 20–40%. - with air and water. The chemical composition of plants, as is known, reflects the elemental composition of soils. Therefore, the excessive accumulation of heavy metals by plants is primarily due to their high concentrations in soils. Despite the significant variability of various plants in the accumulation of heavy metals, the bioaccumulation of elements has a certain tendency, which allows them to be ordered into several groups:

1) Cd, Cs, Rb - elements of intense absorption;

2) Zn, Mo, Cu, Pb, Co, As – average degree of absorption;

3) Mn, Ni, Cr – weak absorption;

4) Se, Fe, Ba, Te are elements that are difficult for plants to access. Another way for heavy metals to enter plants is through foliar absorption from air currents.

The entry of elements into plants through leaves occurs mainly through non-metabolic penetration through the cuticle. Heavy metals absorbed by leaves can be transferred to other organs and tissues and be included in metabolism. Lead and cadmium are highly toxic metals. In roadside plants, the amount of lead is sharply increased, it is 10-100 times higher compared to plants growing away from roads. Large amounts of cadmium are found in plants growing near highways. For example, in the needles of common spruce growing near roads, the amount of cadmium increases by 11–17 times.

The entry of heavy metals into plants can occur directly from the air with dust settling on leaves and needles and translocation from the soil: the share of heavy metals in the composition of dust on the surface of leaves near the source is on average 30% of the total content of heavy metals in them. In depressions and on the windward side, this share can reach up to 60%. As you move away from the source, the role of atmospheric pollution noticeably decreases.

Chapter III . Determination of the presence of heavy metal compounds in the environment and their impact on living organisms

The method for determining the content of heavy metal ions comes down to analyzing melt water, water from a reservoir or water extracts using high-quality reagents.

Qualitative determination of lead ions P b 2+

Potassium iodide gives a characteristic yellow precipitate of lead iodide in solution with lead ions

Progress of the study :

1 ml of water, melt water or aqueous extract from each sample is poured into test tubes and 1 ml of KI solution and 1 ml of 6% HNO are added 3. The test tubes with the contents are left for a day. In the presence of lead ions, a yellow precipitate forms when the lead content is 60 μg in the sample. At lower concentrations, the contents of the test tube turn yellow.:

R b 2+ + I - = R b I 2

Qualitative determination of iron ions

Total iron

Ammonium rhodanideN.H. 4 SCN or potassium KSCN form in an acidic environment withFe 3+ iron thiocyanates, colored blood red. Depending on the concentration of thiocyanate ion, complexes of different types can be formed.composition:

Fe 3+ +SCN - = 2+

Fe 3+ + 2 SCN - = +

Fe 3+ + 3 SCN- = Fe( SCN) 3

To 1 ml of test water add 2-3 drops of hydrochloric acid solution and2- 3 drops of reagent solution.

Atiron content0.1 mg/lappearspinkcoloring,Aatmorehigh content –red.

The maximum permissible concentration of total iron in reservoir water and drinking water is 0.3 mg/l, the limiting organoleptic hazard indicator.

Iron(II)

Potassium hexacyanoferrate(III)K 3 [ Fe( CN) 6 ] , in an acidic environment(pH ~ 3) forms with the Fe cation 2+ Turnboule blue sediment dark bluecolors:

3Fe 2+ + 2 3- = Fe 3 2

To 1 ml of test water add 2-3 drops of sulfuric acid solution and 2-3drops of reagent solution.

Iron(III)

Potassium hexacyanoferrate(II)K 4 [ Fe( CN) 6 ] in a slightly acidic environment with a cationFe 3+ forms a dark blue precipitate of Prussian blue:

4Fe 3+ + 3 4- = Fe 4 3

To 1 ml of test water add 1-2 drops of hydrochloric acid solution and 2 drops of reagent solution.

For the qualitative determination of lead and iron ions, the following equipment, reagents and materials were used.

Equipment: training scales, weights, ruler, tripod with coupling and foot, burette with stopcock, 2 ml measuring pipette, 100 ml and 50 ml beakers, 100 ml measuring cylinder, 250 ml round flat-bottomed flasks, rubber stoppers, conical funnels , filter paper, test tube rack, test tubes, scissors, spatula, glass rods, glass tubes, Petri dishes.

Reagents: concentrated nitric acid (HNO 3 ), potassium iodide solution (KI), 6% nitric acid solution (HNO 3 ), hydrogen peroxide (H 2 ABOUT 2 ), potassium thiocyanate (solution) (KSCN), sulfuric acid (solution) (H 2 SO 4 ), hexacyanoferrate (III) potassium (K 3 [ Fe( CN) 6 ]), hexacyanoferrate (II) potassium (K 4 [ Fe( CN) 6 ), hydrochloric acid (solution) (HCl), boiled water.

Materials: seeds of watercress, thalli of lichens Xanthoria wallata (goldenwort) and Parmelia furrowata.

3.1. Heavy metal compounds in soil

3.1.1. Methodology for determining the presence of heavy metal compounds in soil

Soil samples (approximately 100 g each) were taken at two points: near the highway in the immediate vicinity (Appendix, Fig. 1), in a coniferous forest belt far from the road (Appendix, Fig. 2), where mainly pine and spruce trees grow, and Some deciduous species are also found.

The soil was dried for 5 days.

We weighed 10 g of each soil sample on a pre-balanced balance.

The samples were transferred into round flat-bottomed flasks with designations (soil sample taken near the road - “p road”; soil sample taken in a forest belt - “p forest”). Pour 50 ml of boiled water into each flask, add 1 drop of concentrated nitric acid HNO 3 , shaken for 5 minutes. Left for a day (Appendix, Fig. 3).

Soil extracts were filtered into labeled beakers, using a different filter for each extract (Appendix, Fig. 4).

The resulting filtrates were used to carry out a qualitative determination of the content of lead and iron ions in the soil according to a previously described method.

3.1.2. Results of analysis of the content of heavy compounds

metals in soil

Analysis of samples for the content of lead ions in the soil gave the following results. In a test tube with an aqueous extract from soil taken near the road, no obvious precipitate formed, but the contents of the test tube turned a rich golden brown color, which indicates a fairly significant content of lead ions in this soil sample. In a test tube with an aqueous extract of soil taken in a forest belt, no sediment or obvious change in color was noted (the soil extract initially had a weak pale yellow color, which can be explained by the coloring property of the organic matter contained in the forest soil) (Appendix, Fig. 5, 6) .

Analysis of samples for the content of iron ions in the soil did not give visible changes: when adding reagents, there was no change in color and no precipitation occurred.

3.2. Compounds of heavy metals in natural waters

3.2.1. Methodology for determining the presence of heavy metal compounds in natural waters

1. We took a water sample from the reservoir into a clean container (Appendix, Fig. 7).

2. Filtered a sample of water taken from the lake into a beaker to clean the sample from mechanical impurities.

3. The resulting filtrate was used to carry out a qualitative determination of the content of lead and iron ions in the lake water according to a previously described method.

3.2.2. Compound content analysis results

heavy metals in natural waters

Analysis of samples for the content of lead ions in water gave the following result: no obvious sediment formed, but the contents of the test tube turned a barely visible pale yellow color (Appendix, Fig. 8).

Analysis of samples for the content of iron ions in water did not give visible results: when adding reagents, there was no change in color and no precipitation occurred.

3.3. Heavy metal compounds in the atmosphere

3.3.1. Methodology for determining the presence of heavy metal compounds in the atmosphere

Snow cover

Snow cover accumulates in its composition almost all substances entering the atmosphere. In this regard, it has a number of properties that make it a convenient indicator of pollution not only of precipitation itself, but also of atmospheric air. During the formation of snow cover, due to the processes of dry and wet precipitation of impurities, the concentration of pollutants in the snow turns out to be 2-3 orders of magnitude higher than in the atmospheric air. Therefore, analysis of snow samples gives results with a high degree of reliability. When sampling fromneg must be taken throughout the depth of its deposits into the containers provided for this purpose.

We took dishes for taking snow samples and made markings. Snow samples were taken in 3 places: on the side of the road (Appendix, Fig. 9), in the yard near the house (Appendix, Fig. 10), in a forest belt (Appendix, Fig. 11).

We filled the containers with snow.

We delivered snow to the classroom.

After the snow melted, the melt water was filtered to remove mechanical impurities from the samples (Appendix, Fig. 12).

The resulting filtrates from three samples were used to carry out a qualitative determination of the content of lead and iron ions in the snow (and, therefore, in the atmosphere) according to the previously described method (Appendix, Fig. 13, 14).

Lichens

The sensitivity of lichens to atmospheric pollution has been noted for a long time. Lichens are capable of accumulating elements from the environment in quantities that far exceed their physiological needs. The absence of special organs for water and gas exchange and the extremely low ability for autoregulation lead to a high degree of correspondence between the chemical composition of lichens and their environment. This quality has determined the widespread use of lichens as accumulative bioindicators of environmental pollution with heavy metals. It has been established that Co, Ni, Mo, Au are present in lichens in the same concentrations as in higher plants, and the content of Zn, Cd, Sn, Pb is much higher.

To qualitatively determine the content of heavy metal ions, we used the following method:

Lichens were collected from silver birch (Betula pendula ) and goat willow (Salix caprea ) at a height of 0.5 to 1 meter.

If possible, lichen samples were taken without bark; if it was impossible to separate the thallus from the bark, they were cut off along with it.

For analysis, thalli of the lichens Xanthoria wallata and Parmelia sulcata were collected, and a visual assessment of the condition of the thalli during collection was also carried out.

Sampling was carried out in two places: on trees near the highway (Appendix, Fig. 15, 16) and on trees growing in the forest belt (Appendix, Fig. 17).

Lichens of the same species, collected from one tree, were placed in a common bag with designations (Appendix, Fig. 18).

In the office, 25 g of lichen thalli of each type from each sample were weighed on scales and crushed.

Two samples of lichen thalli of both species (xanthorium + parmelia for each sampling site) were placed in round flat-bottomed flasks, 50 ml of boiled water was poured into each flask, 1 drop of concentrated nitric acid was added, shaken for 5 minutes, and left for a day. (Appendix, Fig. 3).

Then the aqueous extract was filtered and the resulting filtrates were used forcarrying out a qualitative determination of the content of lead and iron ions in lichen thalli (and, therefore, in the atmosphere) according to the previously described method.

3.3.2. Compound content analysis results

heavy metals in the atmosphere

Snow cover

Analysis of samples for the content of lead ions in snow gave the following results. In a test tube with a filtrate of melt water from snow taken on the side of the road (sample No. 3), no obvious sediment formed, but the contents of the test tube turned a bright golden color, which indicates a significant content of lead ions in this snow sample. In a test tube with a filtrate of melt water from snow taken in a forest belt far from the road (sample No. 2), no sediment precipitated; the contents of the test tube acquired a faint pale yellow color. In a test tube with a filtrate of melt water from snow taken in the backyard near the house (sample No. 1), no sediment formed; the contents of the test tube turned pale yellow (Appendix, Fig. 8).

Analysis of samples for the content of iron ions in snow did not give visible results: when adding reagents, there was no change in color and no precipitation occurred.

Lichens

When visually assessing the condition of the thalli of the lichens Xanthoria wallata and Parmelia grooveta, some depression in the general condition of the lichen thalli growing on trees near the road was noted: the thalli are small in size, somewhat thickened, their leafy character is poorly visible, the thalli are firmly attached to the bark of the trees (Appendix, Fig. 19). All this indicates the presence in the atmosphere of the study area (roadside area) of substances that negatively affect living organisms - lichens.

Analysis of samples for the content of lead ions in lichen thalli gave the following results. In a test tube with an aqueous extract from lichen thalli collected from trees near the highway, no sediment precipitated, but the contents of the test tube turned a faint pale yellow color, which indicates lead ions contained in the atmosphere and their accumulation in the lichen thalli. In a test tube with an aqueous extract from lichen thalli collected from trees in a forest belt far from the highway, no sediment formed and no color change was noted (Appendix, Fig. 6).

Analysis of samples for the content of iron ions in lichen thalli did not give visible results: when adding reagents, there was no change in color and no precipitation occurred.

General conclusion: Analyzing the results obtained in all types of experiments (the content of lead ions in soil, water, snow and lichens), we conclude that lead ions are contained in the environment. Moreover, the content of lead ions is greater the closer the sampling area is to places with high human activity (in our case, a highway), which is primarily explained by the entry of lead ions into the environment as part of vehicle exhaust gases. The negative result of tests for the content of iron ions in all variants of the experiments is most likely associated not with the complete absence of iron in the environment, but with its very low content, which cannot be determined by the methods we use and the reagents available in the laboratory.

3.4. Heavy metal compounds and living organisms

3.4.1. Methodology for determining the effects of heavy metal compounds on organisms

We used watercress as a test organism (Appendix, Fig. 20).

Watercress is an annual vegetable plant that is highly sensitive to soil contamination with heavy metals, as well as to air pollution from gaseous emissions from vehicles. This bioindicator is characterized by rapid seed germination and almost one hundred percent germination.

In addition, the shoots and roots of this plant undergo noticeable morphological changes under the influence of pollutants. Growth retardation and curvature of shoots, reduction in the length and weight of roots.

Watercress as a bioindicator is also convenient because the effect of stress can be studied simultaneously on a large number of plants in a small work area. The very short duration of the experiment is also attractive. Watercress seeds germinate on the second or third day.

To determine the impact of heavy metal ions on living organisms (cress), we took samples of melt water, samples of which had already been analyzed for the content of lead and iron ions using high-quality reagents.

Circles cut from filter paper according to the size of the Petri dishes were placed at the bottom of the Petri dishes; Petri dishes were numbered.

3 ml of melt water from the corresponding sample was poured into each Petri dish (the filter paper was completely wetted) (Appendix, Fig. 21).

Watercress seeds were placed on filter paper (20 pieces in each Petri dish) and covered with lids (Appendix, Fig. 22, 23).

After 3 days, a morphometric assessment of the lettuce seedlings was carried out (the length of the roots was measured) (Appendix, Fig. 24, 25).

The data was entered into a table, the average value of root lengths for each option was found, and conclusions were drawn

3.4.2. Compound Exposure Results

heavy metals on living organisms

Morphometric parameters of watercress seedlings

(length of spines in mm)

p/p

Sample No. 1 (snow from the yard)

Sample No. 2 (snow from the forest belt)

Sample No. 3 (snow from the road)

AVERAGE VALUE

44,74

56,24

22,4

Conclusions: Lead ions contained in melt water have a depressing effect on the vital processes of organisms; the higher the content of lead ions in melt water, the greater the negative impact. This follows from the results obtained. In experimental variant No. 3 (road) (Appendix, Fig. 26), morphometric changes are clearly noted: the length of the roots sharply decreases - by 20 mm or more according to average indicators. In addition, germination rate was 90%. In experimental variants No. 1 (yard) (Appendix, Fig. 27) and No. 2 (forest belt) (Appendix, Fig. 28), the germination rate was 95% and 85%, respectively. Such a quantitative scatter in germination in options No. 1 and No. 2 may be associated with the general germination of seed material (random factor) and a relatively small sample. The smaller value of the average root length in option No. 1 compared to option No. 2 is explained by the greater presence of lead ions in the melt water. The negative impact of lead ions on living organisms was clearly established during the experiment.

Conclusion

The environment is a home for living organisms, and it also provides organisms with all the substances necessary for normal life. At the same time, living organisms absorb from their environment not only what they need; there is a joint absorption of a whole complex of substances and elements, some of which are not only not useful, but also have a depressing, poisonous effect on organisms; among such substances, heavy metal compounds. But usually the natural background of heavy metals in the environment is quite low, therefore, the negative impact of their compounds on plants and animals is insignificant.

Recently, the environment has been experiencing a very strong impact from humans, who negatively affect its condition and lead to severe pollution.

In the course of our research, it was found that the degree of anthropogenic impact on the environment in the area of pollution with heavy metal compounds is high. Ions of the heavy metal lead are present in the environment of the study area, and their content increases when approaching areas with a high degree of anthropogenic impact - near highways in the study area. At a distance from roads, the concentration of metal ions decreases, but, nevertheless, the content of heavy metal compounds will be higher than the natural background, because pollution spreads over large areas with moving air masses, with flows of ground and surface water, and with precipitation. Negative tests for the presence of iron ions do not mean its absence; in rural areas there are practically no sources of its entry into the environment, therefore the content of iron ions is extremely low to establish its presence. It was also found that heavy metal ions have a general inhibitory effect on the processes of growth and development of living organisms at relatively low concentrations.

The practical significance of the work lies in the fact that the results obtained can be used: when conducting classroom hours, extracurricular activities and classes devoted to problems of the ecological state of the environment (in particular, the study area); when developing booklets on the topic “The environment and the problem of its pollution by heavy metal compounds” to inform the population (including installing a sign near the reservoir “Fishing is prohibited!”). The practical results of research work can be used when writing an article for a newspaper to highlight the problem of environmental pollution.

Bibliography

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Heavy metals as an environmental hazard factor: Guidelines for independent work on ecology for 3rd year full-time students / Compiled by: Yu.A. Kholopov. – Samara: SamGAPS, 2003.

Application

Fig.1. Taking a soil sample from the side of the road

Fig.2. Soil sampling in a forest belt

Fig.3. Obtaining aqueous extracts from soil and from lichen thalli

Fig.4. Obtaining soil extract filtrate

Fig.5. Soil extract filtrates

Fig.6. Results of detection of lead ions in aqueous extracts from lichen thalli and soil

Fig.7. Taking a water sample from the lake

Fig.8. Results of detection of lead ions in melt water and lake water

Fig.9. Taking a snow sample from the side of the road

Fig. 10. Taking a snow sample in the yard near the house

Fig. 11. Taking a snow sample in a forest belt

Fig. 12. Obtaining melt water filtrate

Fig. 13. Measuring a sample of melt water from a burette into a test tube

Fig. 14. Taking the required amount of reagent into a measuring pipette

Fig. 15. Collection of parmelia furrow lichen near the road

Fig. 16. Collection of Xanthoria wallii lichen near the road

Rice. 17. Collection of Parmelia furrow lichen in a forest belt

Fig. 18. Collected samples of lichen thalli

Fig. 19. Lichens on the trunk of a birch tree growing near the road

Fig.20. Test organism – watercress

Fig.21. Preparing to sow seeds

Fig.22. Sowing watercress seeds

Fig.23. Watercress seeds in Petri dishes

Fig.24. Measuring the root lengths of watercress seedlings

Fig.25. Measuring the root length of a watercress seedling

Fig.26. Watercress sprouts

(experimental option - snow taken near the road)

Fig.27. Watercress sprouts

(experimental option - snow taken from the yard of the house)

Fig.28. Watercress sprouts

(experimental version - snow taken from the forest belt)

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

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Course work

Determination of lead in urban vegetation

Introduction

lead titrimetric metal reagent

Lead is a toxic substance whose accumulation affects a number of body systems and is especially harmful to young children.

Childhood exposure to lead is estimated to contribute to approximately 600,000 new cases of intellectual disability in children each year.

Lead exposure is estimated to cause 143,000 deaths per year, with the heaviest burden in developing regions.

In the body, lead enters the brain, liver, kidneys and bones. Over time, lead accumulates in teeth and bones. Human exposure is typically determined using blood lead levels.

There is no known level of lead exposure that is considered safe.

The main sources of lead pollution are motor vehicles using lead - containing gasoline, metallurgical plants, smoke sources such as thermal power plants, etc.

Plants absorb lead from soil and air.

They perform a useful role for humans, acting as adsorbents for lead in the soil and air. Dust containing lead accumulates on plants without spreading.

According to the data on the content of mobile forms of heavy metals in plants, one can judge the contamination of a certain space with them.

This course work examines the lead content in urban vegetation.

1. Leeliterature review

The literature review is based on the book “Analytical Chemistry of Elements. Lead".

1. 1 AboutGeneral information about lead

Svinemts (lat. Plumbum; denoted by the symbol Pb) is an element of the 14th group (outdated classification - the main subgroup of group IV), the sixth in the periodic system of chemical elements of D.I. Mendeleev, with atomic number 82 and thus contains the magic number of protons. The simple substance lead (CAS number: 7439-92-1) is a malleable, relatively fusible metal of a silvery-white color with a bluish tint. Known since ancient times.

The lead atom has the electronic structure 1s 2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 6 d 10 f 14 5s 2 p 6 d 10 6s 2 p 2 . The atomic mass is assumed to be 207.2, but its fluctuations by 0.03 - 0.04 a.c. are possible.

Lead is a component of more than 200 minerals, but only three of them (galena, anglesite, cerussite) are found in nature in the form of industrial deposits of lead ores. The most important of these is galena PbS (86.5% Pb).

Under the influence of substances dissolved in natural waters and during weathering, it turns into anglesite PbSO 4 (63.3% Pb), which, as a result of double exchange with calcium and magnesium carbonates, forms cerussite PbCO 3 (77.5% Pb).

In terms of industrial production, lead ranks fourth in the group of non-ferrous metals, second only to aluminum, copper and zinc.

For the production of lead, polymetallic sulfide and mixed ores are of greatest importance, since pure lead ores are rare.

It is used for radiation protection purposes, as a structural material in the chemical industry, and for the manufacture of protective coatings for electrical cables and battery electrodes. Large quantities of lead are used to make various alloys: with bismuth (a coolant in nuclear technology), with tin and small additions of gold and copper (solders for the manufacture of printed circuits), with antimony, tin and other metals (solders and alloys for printing and antifriction purposes). The ability to form intermetallic compounds is used to produce lead telluride, from which IR ray detectors and converters of thermal radiation energy into electrical energy are prepared. A large proportion of lead is used in the synthesis of organometallic compounds.

Many lead-containing organic compounds are products of “minor” chemistry, but are of great practical importance. These include lead stearate and phthalate (thermal and light stabilizers for plastics), basic lead fumarate (thermal stabilizer for electrical insulators and vulcanizing agent for chlorosulfopolyethylene), lead diamyldithiocarbamate (multifunctional lubricating oil additive), lead ethylenediaminetetraacetate (radiocontrast agent), lead tetraacetate (oxidizing agent in organic chemistry). Among the practically important inorganic compounds we can name lead oxide (used in the production of glasses with a high refractive index, enamels, batteries and high-temperature lubricants); lead chloride (production of current sources); basic carbonate, lead sulfate and chromate, red lead (paint components); titanate - zirconate. lead (production of piezoelectric ceramics). Lead nitrate is used as a titrant.

The exceptional diversity and importance of the mentioned applications of lead have stimulated the development of numerous methods for the quantitative analysis of various objects. 1.2. Lead content in natural objects

The earth's crust contains 1.6*10 -3% by mass Pb. The cosmic abundance of this element, according to various authors, varies from 0.47 to 2.9 atoms per 106 silicon atoms. For the Solar System, the corresponding value is 1.3 atoms per 10 6 silicon atoms.

Lead is found in high concentrations in many minerals and ores, in micro- and ultra-microquantities - in almost all objects of the surrounding world.

Other objects contain lead (% by weight); rain water - (6-29) * 10 -27, open source water - 2 * 10 -8, sea water - 1.3 open ocean water on the surface - 1.4 * 10 -9, at a depth of 0.5 and 2 km - 1.2*10 -9 and 2* 10 -10, respectively, granites, black shale, basalts - (1 - 30)*10 -4, sedimentary clay minerals - 2*10 -3, volcanic rocks of the Pacific belt - 0 .9*10 -4, phosphorites - from 5*10 -4 to 3*10 -2.

Brown coal - from 10 -4 to 1.75 * 10 -2 , oil - 0.4 4 * 10 -4 , meteorites - from 1.4 * 10 -4 to 5.15 * 10 -2 .

Plants: average content - 1*10 -4, in areas of lead mineralization - 10 -3, food 16*10 -6, puffball mushrooms collected near the highway - 5.3*10 -4, ash: lichens - 10 - 1, coniferous trees - 5*10 -3, deciduous trees and shrubs - up to 3*10 -3. Total lead content (in tons): in the atmosphere - 1.8 * 10 4 , in soils - 4.8 * 10 9 , in sediments - 48 * 10 12 , in ocean waters - 2.7 * 10 7 , in waters rivers and lakes - 6.1 * 10 -4 , in subsoil waters - 8.2 * 10 4 , in water and land organisms: living - 8.4 * 10 4 , dead - 4.6 * 10 6 .

1.2 Issources of lead pollution

Sources of lead in various areas of human and animal habitats are divided into natural (volcanic eruptions, fires, decomposition of dead organisms, sea and wind dust) and anthropogenic (activities of lead producing and processing enterprises, combustion of fossil fuels and waste from its processing).

In terms of the scale of emissions into the atmosphere, lead ranks first among microelements.

A significant portion of the lead contained in coal is released into the atmosphere when burned along with flue gases. The activity of just one thermal power plant, consuming 5000 tons of coal per day, annually releases 21 tons of lead and comparable amounts of other harmful elements into the air. A significant contribution to air pollution with lead comes from the production of metals, cement, etc.

The atmosphere is polluted not only by stable but also by radioactive isotopes of lead. Their source is radioactive inert gases, of which the longest-lived, radon, even reaches the stratosphere. The resulting lead partially returns to the earth with precipitation and aerosols, polluting the soil surface and water bodies.

1.3 Thattoxicity of lead and its compounds

Lead is a poison that affects all living things. It and its compounds are dangerous not only due to their pathogenic effect, but also due to the cumulative therapeutic effect, high accumulation rate in the body, low rate and incomplete excretion with waste products. Lead Hazard Facts:

1. Already at a concentration of 10 -4% in the soil, lead inhibits the activity of enzymes, and highly soluble compounds are especially harmful in this regard.

2. The presence of 2*10 -5% lead in water is harmful to fish.

3. Even low concentrations of lead in water reduce the amount of carotenoid and chlorophyll in algae.

4. Many cases of occupational diseases have been registered among those working with lead.

5. Based on the results of 10 years of statistics, a correlation has been established between the number of deaths from lung cancer and the increased content of lead and other metals in the air of areas of industrial enterprises consuming coal and petroleum products.

The degree of toxicity depends on the concentration, physicochemical state and nature of lead compounds. Lead is especially dangerous in a state of molecular ion dispersion; it penetrates from the lungs into the circulatory system and from there is transported throughout the body. Although lead and its inorganic compounds act qualitatively similarly, their toxicity increases in sync with their solubility in biological fluids of the body. This does not diminish the danger of poorly soluble compounds that change in the intestine with a subsequent increase in their absorption.

Lead inhibits many enzymatic processes in the body. With lead intoxication, serious changes occur in the nervous system, thermoregulation, blood circulation and trophic processes are disrupted, the immunobiological properties of the body and its genetic apparatus change.

1. 4 OSadditive and titrimetric methods

1. Gravimetric method - the formation of weight forms of lead with organic and inorganic reagents is used. Among inorganic ones, preference is given to lead sulfate and chromate. Methods based on their precipitation are comparable in selectivity and conversion factor, but the determination of Pb in the form of chromate requires less time. It is recommended to obtain both sediments using “homogeneous” precipitation methods.

Organic reagents provide weight forms suitable for the determination of smaller quantities of Pb, with more favorable conversion factors than lead chromate or lead sulfate.

Advantages of the method: crystallinity of the precipitate and high accuracy of results in the absence of interfering impurities. Relative error of determination 0.0554-0.2015 Pb< 0,3%. С применением микроаппаратуры выполнены определения 0,125-4,528 мг РЬ с относительной погрешностью < 0,8%. Однако присутствие свободной HN0 3 недопустимо, а содержание солей щелочных металлов и аммония должно быть возможно малым.

2. Precipitation titration with visual indicators. Titration with organic and inorganic reagents is used. In the absence of impurity ions precipitated by chromate, direct titrimetric methods with indication of the titration end point (ETP) by a change in the color of methyl red or adsorption indicators are most convenient. The best option for the titrimetric determination of Pb by the chromate method is the precipitation of PbCr0 4 from an acetic acid solution, followed by dissolving the precipitate in 2 M HC1 or 2 M HC10 4, adding excess potassium iodide and titrating the liberated iodine with Na 2 S 2 0 3.

3. Titration with EDTA solutions. Due to the versatility of EDTA as an analytical reagent for most cations, the question arises of increasing the selectivity of Pb determination. To do this, they resort to preliminary separation of mixtures, the introduction of masking reagents and regulation of the reaction of the medium to pH values > 3. Usually, titration is carried out in a slightly acidic or alkaline medium.

The end point of the titration is most often indicated using metallochromic indicators from the group of azo- and triphenylmethane dyes, derivatives of diatomic phenols and some other substances, the colored Pb complexes of which are less stable than ethylenediaminetetraacetate of lead. In weakly acidic media, titrate against 4 - (2-pyridylazo)-resorcinol, thiazolyl-azo-and-cresol, 2 - (5-bromo-2-pyridylazo) - 5-diethylaminophenol, 1 - (2-pyridylazo) - 2-naphthol , 2 - (2-thiazolylazo) - resorcinol, azo derivatives of 1-naphthol4-sulfonic acid, xylenol orange, pyrocatechol violet, methylxylenol blue, pyrogallol and bromopyrogallol red, methylthymol blue, hematoxylin, sodium rhodizonate, alizarin S and dithizone.

In alkaline environments, eriochrome black T, sulfarsazene, 4 - (4,5 - dimegyl-2-thiazolylazo) - 2-methylresorcinol, a mixture of acid alizarin black SN and eriochrome red B, pyrocatecholphthalein, strong solochrome 2 RS, methylthymol blue and murexide ( titration of total amounts of Pb and Cu).

4. Titration with other complexing substances. The formation of chelates with DCTA, TTGA, and sulfur-containing complexing agents is used.

1.5 Fotometric methods of analysisabout light absorption and scattering

1. Determination as sulfide. The origins of this method and its first critical assessment date back to the beginning of our 20th century. The color and stability of a PbS sol depend on the particle size of the dispersed phase, which is influenced by the nature and concentration of dissolved electrolytes, the reaction of the medium, and the preparation method. Therefore, these conditions must be strictly observed.

The method is not very specific, especially in an alkaline environment, but the convergence of results in alkaline solutions is better. In acidic solutions, the sensitivity of determination is lower, but it can be slightly increased by adding electrolytes, for example NH 4 C1, to the analyzed sample. The selectivity of determination in an alkaline medium can be improved by introducing masking complexing agents.

2. Determination in the form of complex chlorides. It has already been indicated that Pb chlorine complexes absorb light in the UV region, and the molar extinction coefficient depends on the concentration of Cl ions - In a 6 M HCl solution, the absorption maxima of Bi, Pb and Tl are sufficiently distant from each other, which makes it possible to simultaneously determine them by light absorption at 323, 271 and 245 nm, respectively. The optimal concentration range for determining Pb is 4-10*10-4%.

3. Determination of Pb impurities in concentrated sulfuric acid is based on the use of characteristic absorption at 195 nm relative to a standard solution, which is prepared by dissolving lead in H2S04 (special purity).

Determination using organic reagents.

4. In the analysis of various natural and industrial objects, the photometric determination of Pb using dithizone, due to its high sensitivity and selectivity, occupies a leading place. In various variants of existing methods, the photometric determination of Pb is performed at the wavelength of the maximum absorption of dithizone or lead dithizonate. Other variants of the dithizone method are described: photometric titration without phase separation and a non-extraction method for the determination of lead in polymers, in which a solution of dithizone in acetone is used as a reagent, diluted with water before use to a concentration of the organic component of 70%.

5. Determination of lead by reaction with sodium diethyldithiocarbamate. Lead is easily extracted by CCl4 in the form of colorless diethyldithiocarbamate at various pH values. The resulting extract is used in the indirect method for determining Pb, based on the formation of an equivalent amount of yellow-brown copper diethyldithiocarbamate as a result of exchange with CuS04.

6. Determination by reaction with 4 - (2-pyridylazo) - resorcinol (PAR). The high stability of the red Pb complex with PAR and the solubility of the reagent in water are the advantages of the method. For the determination of Pb in some objects, for example in steel, brass and bronze, a method based on the formation of a complex with this azo compound is preferable to the dithizone one. However, it is less selective and therefore, in the presence of interfering cations, requires preliminary separation by the HD method or extraction of lead dibenzyldithiocarbamate with carbon tetrachloride.

7. Determination by reaction with 2 - (5-chloropyridip-2-azo) - 5-diethylaminophenol and 2 - (5-bromopyridyl-2-azo) - 5-diethylaminophenol. Both reagents form 1:1 complexes with Pb with almost identical spectrophotometric characteristics.

8. Determination by reaction with sulfarsazene. The method uses the formation of a reddish-brown water-soluble complex of composition 1: 1 with an absorption maximum at 505-510 nm and a molar extinction coefficient of 7.6 * 103 at this wavelength and pH 9-10.

9. Determination by reaction with arsenazo 3. This reagent, in the pH range 4-8, forms a blue complex with a composition of 1:1 with lead with two absorption maxima - at 605 and 665 nm.

10. Determination by reaction with diphenylcarbazone. In terms of reaction sensitivity, when extracting the chelate in the presence of KCN, and in terms of selectivity, it approaches dithizone.

11. Indirect method for determining Pb using diphenylcarbazide. The method is based on the precipitation of lead chromate, its dissolution in 5% HC1 and the photometric determination of dichromic acid by reaction with diphenylcarbazide using a filter with a maximum transmission at 536 nm. The method is time-consuming and not very accurate.

12. Determination by reaction with xylenol orange. Xylenol orange (KO) forms a 1:1 complex with lead, the optical density of which reaches its limit at pH 4.5-5.5.

13. Determination by reaction with bromopyrogalpol red (BOD) in the presence of sensitizers. Diphenylguanidinium, benzylthiuronium and tetraphenylphosphonium chlorides are used as sensitizers that increase the color intensity but do not affect the position of the absorption maximum at 630 nm, and cetyltrimethylammonium and cetylpyridinium bromides at pH 5.0.

14. Determination by reaction with glycinthymol blue. The complex with glycinthymol blue (GBL) of composition 1:2 has an absorption maximum at 574 nm and a corresponding molar extinction coefficient of 21300 ± 600.

15. Determination with methylthymol blue is performed under conditions similar to those for the formation of a complex with GTS. In terms of sensitivity, both reactions are close to each other. Light absorption is measured at pH 5.8-6.0 and a wavelength of 600 nm, which corresponds to the position of the absorption maximum. The molar extinction coefficient is 19,500. Interference from many metals is eliminated by masking.

16. Determination by reaction with EDTA. EDTA is used as a titrant in indicator-free and indicator photometric titrations (PT). As in visual titrimetry, reliable FT with EDTA solutions is possible at pH > 3 and titrant concentration of at least 10-5 M.

Luminescent analysis

1. Determination of Pb using organic reagents

A method has been proposed in which the intensity of chemiluminescence emission is measured in the presence of Pb due to the catalytic oxidation of luminol with hydrogen peroxide. The method was used to determine from 0.02 to 2 μg Pb in 1 ml of water with an accuracy of 10%. The analysis lasts 20 minutes and does not require preliminary sample preparation. In addition to Pb, the oxidation reaction of luminol is catalyzed by traces of copper. The method, which is much more complex in its hardware design, is based on the use of the fluorescence quenching effect of fluores-132 derivatives and is valuable in the formation of chelates with lead. More selective in the presence of many geochemical satellites of Pb, although less sensitive, is a fairly simple method based on increasing the fluorescence intensity of the water-blue lumogen in a dioxane-water mixture (1: 1) in the presence of Pb.

2. Methods of low-temperature luminescence in frozen solutions. Freezing the solution is most easily solved in the method for determining lead in HC1, based on photoelectric recording of the green fluorescence of chloride complexes at -70°C.

3. Analysis of the luminescence burst during defrosting of samples. The methods of this group are based on a shift in the luminescence spectra when the analyzed sample is thawed and measurement of the observed increase in radiation intensity. The maximum wavelength of the luminescence spectrum at -196 and -70°C is 385 and 490 nm, respectively.

4. A method is proposed based on measuring the analytical signal at 365 nm in the quasi-line luminescence spectrum of CaO-Pb crystal phosphorus cooled to liquid nitrogen temperature. This is the most sensitive of all luminescent methods: if an activator is applied to the surface of tablets (150 mg CaO, diameter 10 mm, pressing pressure 7-8 MN/m2), then the detection limit on the ISP-51 spectrograph is 0.00002 μg. The method is characterized by good selectivity: a 100-fold excess of Co, Cr(III), Fe (III), Mn(II), Ni, Sb (III) and T1 (I) does not interfere with the determination of Pb. Bi can also be determined simultaneously with Pb.

5. Determination of lead by the luminescence of a chloride complex sorbed on paper. In this method, luminescent analysis is combined with the separation of Pb from interfering elements using a ring bath. The determination is carried out at ordinary temperature.

1.6 Alelectrochemical methods

1. Potentiometric methods. Direct and indirect determination of lead is used - titration with acid-base, complexometric and precipitation reagents.

2. Electrogravimetric methods use the deposition of lead on electrodes, followed by weighing or dissolution.

3. Coulometry and coulometric titration. Electrogenerated sulfhydryl reagents are used as titrants.

4. Volt-amperometry. Classical polarography, which combines rapidity with fairly high sensitivity, is considered one of the most convenient methods for determining Pb in the concentration range of 10-s-10 M. In the vast majority of works, lead is determined by the reduction current of Pb2+ to Pb° on a mercury dropping electrode (DRE), usually occurring reversibly and in the diffusion mode. As a rule, cathodic waves are well expressed, and polarographic maxima are especially easily suppressed by gelatin and Triton X-100.

5. Amperometric titration

In amperometric titration (AT), the equivalence point is determined by the dependence of the current value of the electrochemical transformation of Pb and (or) titrant at a certain value of the electrode potential on the titrant volume. Amperometric titration is more accurate than the conventional polarographic method, does not require mandatory temperature control of the cell, and is less dependent on the characteristics of the capillary and indifferent electrolyte. It should be noted that the AT method has great potential, since analysis is possible using an electrochemical reaction involving both Pb itself and the titrant. Although the total time spent on AT execution is greater, it is fully compensated by the fact that there is no need for calibration. Titration is used with solutions of potassium dichromate, chloranilic acid, 3,5-dimethyldimercapto-thiopyrone, 1,5-6 is (benzylidene)-thio-carbohydrazone, thiosalicylamide.

1.7 FiPhysical methods for lead determination

Lead is determined by atomic emission spectroscopy, atomic fluorescence spectrometry, atomic absorption spectrometry, X-ray methods, radiometric methods, radiochemical and many others.

2 . ExperimentalPart

2.1 MehDefinition code

This work uses the determination of lead in the form of a dithizonate complex.

Figure 1 - structure of dithizone:

The maximum absorption of lead dithizonate complexes is 520 nm. Photometry is used against a solution of dithizone in CCl 4 .

Double ashing of the test sample is carried out - dry and “wet” method.

Double extraction and reaction with auxiliary reagents serve to separate interfering impurities and ions, and increase the stability of the complex.

The method is highly accurate.

2. 2 Etctests and reagents

Spectrophotometer with cuvettes.

Drying cabinet.

Muffle furnace.

Electric stove.

Electronic balance

Drip funnel 100 ml.

Chemical vessels.

A weighed portion of dry plant material 3 pcs. 10 gr.

0.01% solution of dithizone in CCl 4 .

0.02 N HCl solution.

0.1% hydroxylamine solution.

10% solution of yellow blood salt.

10% solution of ammonium citrate.

10% HCl solution.

Ammonia solution.

Soda solution.

Indicators are thymol blue and phenol red.

Standard solutions of lead, with its content from 1,2,3,4,5,6 µg/ml.

2. 3 Etcpreparation of solutions

1. 0.1% hydroxylamine solution.

W=m water/m solution =0.1%. The mass of the solution is 100 g. Then the weight is 0.1 g. Dissolved in 99.9 ml of double-distilled water.

2.10% solution of yellow blood salt. W=m water/m solution =10%. The mass of the solution is 100 g. Then the weight is 10 g. Dissolved in 90 ml of double-distilled water.

3.10% ammonium citrate solution. W=m water/m solution =10%. The mass of the solution is 100 g. Weight - 10 g. Dissolved in 90 ml of double-distilled water.

4.10% HCl solution. Prepared from concentrated HCl:

You need 100 ml of solution with W=10%. d conc HCl = 1.19 g/ml. Therefore, it is necessary to take 26 g of concentrated HCl, V = 26/ 1.19 = 21.84 ml. 21.84 ml of concentrated HCl was diluted to 100 ml with double-distilled water in a 100 ml volumetric flask to the mark.

5. 0.01% solution of dithizone in CCl4. W=m water/m solution =10%. The mass of the solution is 100 g. Then the weight is 0.01 g. Dissolved in 99.9 ml CCl 4.

6. Soda solution. Prepared from dry Na 2 CO 3 .

7. 0.02 N HCl solution. W=m v-va /m r-ra =? Conversion to mass fraction. 1 liter of 0.02 N HCl solution contains 0.02 * 36.5 = 0.73 g of HCl solution. d conc HCl = 1.19 g/ml. Therefore, you need to take 1.92 g of concentrated HCl, volume = 1.61 ml. 1.61 ml of concentrated HCl was diluted to 100 ml with double-distilled water in a 100 ml volumetric flask to the mark.

9. A solution of the thymol blue indicator was prepared from a dry substance by dissolving it in ethyl alcohol.

2. 4 Mehshaking influences

In an alkaline environment containing cyanide, dithizone extracts thallium, bismuth and tin (II) together with lead. Thallium does not interfere with colorimetric determination. Tin and bismuth are removed by extraction in an acidic medium.

The determination does not interfere with silver, mercury, copper, arsenic, antimony, aluminum, chromium, nickel, cobalt and zinc in concentrations not exceeding twelve times the concentration of lead. The interfering influence of some of these elements, if present in fifty-fold concentrations, is eliminated by double extraction.

Determination is hampered by manganese, which, when extracted in an alkaline medium, catalytically accelerates the oxidation of dithizone with atmospheric oxygen. This interference is eliminated by adding hydroxylamine hydrochloride to the extracted sample.

Strong oxidizing agents interfere with the determination because they oxidize dithizone. Their reduction with hydroxylamine is included in the determination.

2. 5 Thoseexperimental technique

The plant material was dried in a drying oven in a crushed state. Drying was carried out at a temperature of 100 0 C. After drying to an absolutely dry state, the plant material was thoroughly crushed.

Three 10 g portions of dry material were taken. They were placed in a crucible and placed in a muffle furnace, where they were ashed for 4 hours at a temperature of 450 0 C.

Afterwards, the plant ash was soaked in nitric acid while heating and dried (from here on - the operations are repeated for all samples).

Then the ash was again treated with nitric acid, dried on an electric stove and placed in a muffle furnace for 15 minutes at a temperature of 300 0 C.

Afterwards, the clarified ash was dug in with hydrochloric acid, dried, and dug in again. The samples were then dissolved in 10 ml of 10% hydrochloric acid.

Next, the solutions were placed in 100 ml dropping funnels. 10 ml of a 10% solution of ammonium citrate was added, then the solution was neutralized with ammonia until the color of thymol blue turned blue.

After this, extraction was carried out. 5 ml of a 0.01% solution of dithizone in CCl 4 was added. The solution in the dropping funnel was shaken vigorously for 5 minutes. The dithizone layer, after being separated from the main solution, was drained separately. The extraction operation was repeated until the initial color of each new portion of dithizone stopped turning red.

The aqueous phase was placed in a dropping funnel. It was neutralized with a soda solution until the color changed from phenol red to orange. Then 2 ml of a 10% yellow blood salt solution, 2 ml of a 10% ammonium citrate solution, and 2 ml of a 1% hydroxylamine solution were added.

Then the solutions were neutralized with a soda solution until the color of the indicator (phenol red) turned crimson.

Next, 10 ml of a 0.01% solution of dithizone in CCl 4 was added, the sample was vigorously shaken for 30 seconds, then the dithizone layer was poured into a cuvette and spectophotometered against a solution of dithizone in CCl 4 at 520 nm.

The following optical densities were obtained:

The calibration graph was constructed under the same conditions; standard solutions of lead concentrations from 1 to 6 μg/ml were used. They were prepared from a lead solution with a concentration of 1 μg/ml.

2.6 ReExperiment resultsenta and statistical processing

Data for constructing a calibration graph

Calibration chart

According to the calibration graph, the concentration of lead in one kilogram of dry plant mass is equal to

1) 0.71 mg/kg

2) 0.71 mg/kg

3) 0.70 mg/kg

What follows from the determination conditions is that the lead concentration in the standards is measured in μg/ml; for the analysis, the lead content was measured in 10 ml, recalculated for one kilogram of dry plant material.

Average mass value: X av = 0.707 g.

Variance =0.000035

Standard deviation: = 0.005787

Youwater

1. Based on a literature review.

Using a literature review, general information about the element, its determination methods was studied, and the most suitable one was selected according to its accuracy and compliance with those used in everyday practice.

2. Based on the results of the experiment.

The experiment showed that the method can be used to determine low lead contents; the results are highly accurate and repeatable.

3. In accordance with MPC.

List of references used

1. Polyansky N.G. Svinets.-M.: Nauka, 1986. - 357 p. (Analytical chemistry of elements).

2. Vasiliev V.P. Analytical chemistry. At 2 p.m. 2. Physico-chemical methods of analysis: Textbook. For chemical technology Specialist. Vuzov.-M.: Higher. school, 1989. - 384 p.

3. Fundamentals of analytical chemistry. In 2 books. Book 2. Methods of chemical analysis: Textbook. For universities/Yu.A. Zolotov, E.N. Dorokhova, V.I. Fadeeva and others. Ed. Yu.A. Zolotova. - 2nd ed., revised. And additional - M.: Higher. school, 2002. - 494 p.

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conclusions

The systematic hydrogen sulfide method for the analysis of metal cations and arsenic, currently used in forensic chemistry practice, is outdated.
The fractional method of analysis of metal and arsenic cations currently being developed makes it possible to reduce the time of forensic chemical analysis by 2-3 times compared to the hydrogen sulfide method, increase sensitivity in some cases by 100 and even 2000 times, increase the evidence of detection of metals and arsenic, and significantly reduce the consumption of reagents and abandon the use of hydrogen sulfide, which pollutes the air in laboratories.

1 Tananaev N. A. Fractional analysis. M., 1950.

Lead is poisonous and has cumulative properties (the ability to accumulate in the body). As a result, the presence of lead in all types of canned food is not allowed.

The main sources of lead in canned food are semi-deposits, the lead content of which is limited to 0.04%, and solder. The presence of substances in canned products that can dissolve metals can lead to the transition of lead into the contents of the can during long-term storage of canned food. The lead content in the product is determined in the case of long-term storage and the presence of solder deposits on the inside of the can.

The method is based on obtaining a solution of lead chloride after ashing a sample of the product, precipitation of metal sulfides from the solution and determination of lead in a saturated solution of sodium acetate in the presence of potassium dichromate.

Analysis procedure: 15 g of the crushed product is placed in a porcelain cup with a diameter of about 7 cm, dried in a sand bath or in a drying cabinet, and then carefully charred and ashed over low heat or in a muffle furnace with the walls of the muffle glowing slightly red. Add 5 ml of dilute hydrochloric acid (ratio 1:1), 1 drop of hydrogen peroxide to the ash and evaporate to dryness in a water bath. 2 ml of 10% hydrochloric acid and 3 ml of water are added to the dry residue, after which the contents of the cup are filtered through a filter pre-moistened with water into a conical flask with a capacity of 100 ml. The cup and filter are washed with 15 ml of distilled water, collecting the washing water in the same flask. The resulting solution is heated to 40-50 ˚C, passing hydrogen sulfide through it for 40-60 minutes through a narrow tube reaching the bottom of the flask. In this case, lead, tin, and copper sulfides precipitate. The precipitate of sulfides and sulfur is separated by centrifugation in a 10 ml test tube. The liquid is drained, and the precipitate of metal sulfides is washed 1–2 times with a 1% solution of hydrochloric acid saturated with hydrogen sulfide. To the washed sulfide precipitate, immediately add 5 drops of a 10% sodium hydroxide solution (to avoid oxidation of lead sulfide into alkali-soluble sulfate), heat in a boiling water bath, add 10 ml of water and centrifuge. If there is a large sediment, treatment with sodium hydroxide is carried out twice.

To the precipitate of lead and copper sulfides add 5-10 drops of a mixture of strong sulfuric and nitric acids, taken in equal quantities, and carefully heat them on a small burner flame until the nitric acid vapors are completely removed and white thick sulfur trioxide vapors appear. After cooling, add 0.5–1.5 ml of distilled water and the same amount of ethanol to the test tube. If after adding water and alcohol the solution remains clear, then lead salts are considered undetected. When turbidity appears in the solution or a white precipitate forms, lead sulfate is separated with diluted ethanol (ratio 1:1). To the lead sulfate precipitate remaining in the centrifuge tube, add 1 ml of a saturated solution of sodium acetate, previously slightly acidified with acetic acid, and heat in a boiling water bath for 5 - 10 minutes. Then add 1 ml of distilled water, after which the contents of the test tube are filtered through a small filter moistened with distilled water. The filtrate is collected in a 10 ml graduated cylinder. The test tube and filter are washed several times with small portions of distilled water, collecting the wash water in the same cylinder. The volume of the solution is adjusted to the mark with water and mixed. 5 ml of solution from the cylinder is transferred to a centrifuge tube, 3 drops of 5% potassium dichromate solution are added and mixed. If the solution remains clear for 10 minutes, it is considered that no lead has been detected. If lead is present in the solution, a yellow turbidity (PbCrO4) appears. In this case, a quantitative determination of lead is carried out.

To quantify lead, a certain volume of solution (0.5 - 2 ml) is transferred from the cylinder into a flat-bottomed test tube with divisions of 10 ml. A standard solution with a lead content of 0.01 is added to three other similar test tubes; 0.015 and 0.02 mg. In test tubes with a standard solution, add such an amount of saturated sodium acetate solution, slightly acidified with acetic acid, so that its content in the test and standard solutions is the same (if 1 ml of the test solution is taken for the quantitative determination of lead, then 0. 1 ml sodium acetate). Next, distilled water to 10 ml is added to all four test tubes, mixed and 3 drops of a 5% solution of potassium dichromate are added. The contents of the test tube are mixed well and after 10–15 minutes the turbidity of the test solution is compared with the turbidity of standard solutions.

X= (A·10·1000)/ V·15, (6)

Where X - lead content in 1 kg of product, mg;

A– amount of lead in a test tube with a standard solution, mg;

10 – volume of dilution, ml;

V– volume of solution taken for comparison with the standard solution, ml; 15 – weight of product, g.

Preparation of a standard solution of lead nitrate. 160 mg of lead nitrate is dissolved in a small amount of distilled water in a 100 ml volumetric flask, add 1 drop of concentrated nitric acid, mix and adjust the volume to the mark with distilled water; 1 ml of such a solution contains 1 mg of lead, 2 ml of the solution is transferred to a 100 ml volumetric flask, and the volume is adjusted to the mark with distilled water. The last solution is standard. 1 ml contains 0.02 mg of lead.

Essay

The course work contains: ___ pages, 4 tables, 2 figures, 8 literary sources. The object of research in the course work is food products of complex chemical composition.

The purpose of the work is to determine the lead content in food products and compare it with the MPC.

The research method is atomic absorption.

Sample preparation methods are given. Data on the content of lead compounds in food objects (objects) were analyzed and summarized.

Area of application: analytical and toxicological chemistry, laboratories for standardization and quality of food products produced by light industry, pharmaceutical chemistry.

Key words: LEAD, ATOMIC ABSORPTION SPECTROSCOPY, ABSORPTION, STANDARD SOLUTION, CALIBRATION GRAPH, CONTENTS, MPC

Introduction

1. Literature review

1.3 Sample preparation

2. Experimental part

conclusions

Introduction

The use of materials containing lead and its compounds has led to the pollution of many environmental objects. Determination of lead in metallurgical products, biological materials, soils, etc. presents difficulties because it is usually accompanied by other divalent metals. To solve such an analytical problem, the atomic absorption method of determination has become widespread due to the availability of equipment, high sensitivity and sufficient accuracy.

Food products can contain not only useful substances, but also quite harmful and dangerous for the human body. Therefore, the main task of analytical chemistry is food quality control.

Namely, this course work uses the atomic absorption method for determining lead in coffee.

1. Literature review

1.1 Chemical properties of lead

In the periodic table D.I. Mendeleev's lead is located in group IV, the main subgroup, and has an atomic weight of 207.19. Lead in its compounds can be in the oxidation state +4, but the most characteristic for it is +2.

In nature, lead occurs in the form of various compounds, the most important of which is the lead luster PbS. The abundance of lead in the earth's crust is 0.0016 wt. %.

Lead is a bluish-white heavy metal with a density of 11.344 g/cm 3. It is very soft and can be easily cut with a knife. Lead melting point 327.3 O C. In air, lead quickly becomes covered with a thin layer of oxide, protecting it from further oxidation. In the voltage series, lead comes immediately before hydrogen; its normal potential is - 0.126 V.

Water by itself does not react with lead, but in the presence of air, lead is gradually destroyed by water to form lead hydroxide:

Pb+O 2+ H2 O=2Pb(OH) 2

However, when it comes into contact with hard water, lead becomes covered with a protective film of insoluble salts (mainly lead sulfate and basic lead carbonate), which prevents further action of water and the formation of hydroxide.

Dilute hydrochloric and sulfuric acids do not act on lead due to the low solubility of the corresponding lead salts. Lead easily dissolves in nitric acid. Organic acids, especially acetic acid, also dissolve lead in the presence of atmospheric oxygen.

Lead also dissolves in alkalis, forming plumbites.

1.2 Physiological role of lead

The metabolism of lead in humans and animals has been studied very little. Its biological role is also not completely clear. It is known that lead enters the body with food (0.22 mg), water (0.1 mg) and dust (0.08 mg). Typically, the lead content in a man's body is about 30 µg%, and in women it is about 25.5 µg%.

From a physiological point of view, lead and almost all its compounds are toxic to humans and animals. Lead, even in very small doses, accumulates in the human body, and its toxic effect gradually increases. When lead poisoning occurs, gray spots appear on the gums, the functions of the nervous system are disrupted, and pain is felt in the internal organs. Acute poisoning leads to severe damage to the esophagus. For people who work with lead, its alloys or compounds (for example, printing workers), lead poisoning is an occupational disease. The dangerous dose for an adult lies in the range of 30-60 g Pb (CH3COO) 2 * 3H 2ABOUT .

1.3 Sample preparation

The selection and preparation of laboratory samples is carried out in accordance with the normative and technical documentation for this type of product. Two parallel samples are taken from the combined laboratory sample.

Products with a high sugar content (confectionery, jams, compotes) are treated with sulfuric acid (1: 9) at the rate of 5 cm 3 acid per 1 g of dry matter and incubated for 2 days.

Products with a fat content of 20-60% (cheese, oil seeds) are treated with nitric acid (1:

) based on 1.5 cm 3 acid per 10 g of dry matter and incubated for 15 minutes.

Samples are dried in an oven at 150 O C (if there are no aggressive acid fumes) on an electric stove with low heat. To speed up sample drying, simultaneous irradiation of samples with an IR lamp can be used.

Dried samples are carefully charred on an electric stove or gas burner until the emission of smoke stops, preventing ignition and emissions.

Place the crucibles in a cold electric furnace and increase its temperature by 50 O Every half hour, bring the oven temperature to 450 O C. At this temperature, mineralization is continued until gray ash is obtained.

The ash cooled to room temperature is moistened dropwise with nitric acid (1:

) based on 0.5-1 cm 3 weighed acids, evaporated in a water bath and dried on an electric stove with low heat. Place the ash in an electric furnace and bring its temperature to 300 O C and kept for 0.5 hours. This cycle (acid treatment, drying, ashing) can be repeated several times.

Mineralization is considered complete when the ash becomes white or slightly colored without charred particles.

Wet mineralization. The method is based on the complete decomposition of the organic substances of the sample when heated in a mixture of concentrated nitric acid, sulfuric acid and hydrogen peroxide and is intended for all types of food products, butter and animal fats.

A weighed portion of liquid and puree products is added to a flat-bottomed flask, wetting the walls of a 10-15 cm glass 3bidistilled water. You can take the sample directly into a flat-bottomed flask.

A sample of solid and pasty products is taken onto an ash-free filter, wrapped in it and placed with a glass rod on the bottom of a flat-bottomed flask.

Drink samples are taken with a pipette, transferred to a Kjeldahl flask and evaporated on an electric stove to 10-15 cm3 .

A weighed portion of dry products (gelatin, egg powder) is placed in a flask and 15 cm is added 3bidistilled water, stir. Gelatin is left for 1 hour to swell.

Sample mineralizationMineralization of samples of raw materials and food products except vegetable oils, margarine, edible fats:

Nitric acid is added to the flask to calculate 10 cm 3for every 5 g of product and incubate for at least 15 minutes, then add 2-3 clean glass beads, close with a pear-shaped stopper and heat on an electric stove, first weakly, then more strongly, evaporating the contents of the flask to a volume of 5 cm3 .

Cool the flask, add 10 cm 3nitric acid, evaporate to 5 cm 3. This cycle is repeated 2-4 times until the brown fumes stop.

Add 10 cm to the flask 3nitric acid, 2 cm 3sulfuric acid and 2 cm 3hydrogen peroxide for every 5 g of product (mineralization of dairy products is carried out without adding sulfuric acid).

To remove residual acids, add 10 cm 3double-distilled water, heat until white vapor appears and then boil for another 10 minutes. Cool. Adding water and heating is repeated 2 more times.

If a precipitate forms, add 10 cm 3bidistilled water, 2 cm 3sulfuric acid, 5 cm 3hydrochloric acid and boil until the precipitate dissolves, adding evaporating water. After dissolving the precipitate, the solution is evaporated in a water bath to wet salts.

Mineralization of vegetable oils, margarine, edible fats:

lead food chemistry

The flask with the sample is heated on an electric stove for 7-8 hours until a viscous mass is formed, cooled, and 25 cm 3nitric acid and carefully heat again, avoiding violent foaming. After foaming stops, add 25 cm 3nitric acid and 12 cm 3hydrogen peroxide and heat until a colorless liquid is obtained. If the liquid darkens, periodically add 5 cm 3nitric acid, continuing heating until mineralization is complete. Mineralization is considered complete if the solution remains colorless after cooling.

Acid extraction. The method is based on the extraction of toxic elements with dilute (1:

) by volume with hydrochloric acid or diluted (1: 2) by volume with nitric acid and is intended for vegetable and butter oils, margarine, edible fats and cheeses.

Extraction is carried out in a heat-resistant sample of the product. Add 40 cm into the flask using a cylinder. 3solution of hydrochloric acid in double-distilled water (1:

) by volume and the same amount of nitric acid (1: 2). Several glass beads are added to the flask, a refrigerator is inserted into it, placed on an electric stove, and boiled for 1.5 hours from the moment of boiling. Then the contents of the flask are slowly cooled to room temperature without removing the refrigerator.

The flask with the extraction mixture of butter, fats or margarine with acid is placed in a cold water bath to solidify the fat. The hardened fat is pierced with a glass rod, the liquid is filtered through a filter moistened with the acid used for extraction into a quartz or porcelain bowl. The fat remaining in the flask is melted in a water bath, add 10 cm 3acids, shake, cool, after cooling the fat is calcined and the liquid is poured through the same filter into the same bowl, then washed 5-7 cm 3bidistilled water.

The extraction mixture of vegetable oil and acid is transferred to a separatory funnel. The flask is rinsed 10 cm 3acid, which is poured into the same funnel. After phase separation, the lower aqueous layer is poured through an acid-soaked filter into a quartz or porcelain bowl, the filter is washed 5-7 cm 3bidistilled water.

The extraction mixture of cheese and acid is filtered through an acid-soaked filter into a quartz or porcelain bowl. The flask is rinsed 10 cm 3acid, which is filtered through the same filter, then the filter is washed 5-7 cm 3bidistilled water.

The filtered extract is carefully evaporated and charred on an electric stove, and then ashed in an electric oven.

1.4 Lead determination methods

1.4.1 Concentration of trace amounts of lead ion using nanometer particles of titanium dioxide (anatase) for the purpose of their subsequent determination by inductively coupled plasma atomic emission spectrometry with electrothermal evaporation of the sample

Inductively coupled plasma atomic emission spectrometry ( ISP-AES) -a widely used and very promising method of elemental analysis. However, it has some disadvantages, including relatively low detection sensitivity, low sputtering efficiency, spectral interference and other matrix effects. Therefore, ICP-AES does not always meet the requirements of modern science and technology. The combination of ICP-AES with electrothermal evaporation of the sample (ETI-ICP-AES) significantly expands the capabilities of the method. By optimizing the pyrolysis and evaporation temperatures, analyte elements can be evaporated sequentially, separating them from the sample matrix. This method has the advantages of high sample introduction efficiency, the ability to analyze small sample quantities, low absolute detection limits, and the ability to directly analyze solid samples.

Analysis tools and conditions.An ICP generator with a power of 2 kW and a frequency of 27 ± 3 MHz was used; ISP burner; graphite furnace WF-1A; diffraction spectrometer RO5-2 with a diffraction grating of 1300 lines/mm with a linear dispersion of 0.8 nm/mm; pH meter Mettle Toledo 320-S; sedimentation centrifuge model 800.

Standard solutions and reagents.Stock standard solutions with a concentration of 1 mg/ml are prepared by dissolving the corresponding oxides (spectroscopic purity) in diluted HC1, followed by dilution with water to a given volume. A suspension of polytetrafluoroethylene was added to each standard solution to a concentration of 6% w/v.

We used Triton X-100 reagent grade (USA). The remaining reagents used were of spectroscopic grade; double distilled water. Titanium dioxide nanoparticles with a diameter of less than 30 nm.

Method of analysis.The required volume of solution containing metal ions is placed in a 10 ml graduated test tube and the pH is adjusted to 8.0 using 0.1 M HC1 and an aqueous solution of NH 3. Then 20 mg of titanium dioxide nanoparticles are added to the test tube. Shake the test tube for 10 minutes. (preliminary experiments showed that this is sufficient to achieve adsorption equilibrium). The tube is left for 30 minutes, then the liquid phase is removed using a centrifuge. After washing the precipitate with water, 0.1 ml of a 60% polytetrafluoroethylene suspension, 0.5 ml of a 0.1% agar solution, 0.1 ml are added to it. Triton X-100 and diluted with water to 2.0 ml. The mixture is then dispersed using an ultrasonic vibrator for 20 minutes to achieve homogeneity of the suspension before it is introduced into the evaporator. 20 μl of the suspension is added to the graphite furnace after heating and stabilization of the ICP. After drying, pyrolysis and evaporation, the sample vapor is transferred to the ICP by a current of carrier gas (argon); atomic emission signals are recorded. Before each sample injection, the graphite furnace is heated to 2700°C to clean it.

Application of the method.The developed method is used to determine Pb 2+in samples of natural lake water and river water. Water samples were filtered through a 0.45 µm membrane filter immediately after sampling and then analyzed.

1.4.2 Determination of lead combining real-time concentration followed by reversed-phase HPLC

Instruments and reagents. A diagram of the HPLC system with real-time concentration ("on-line") is shown in Fig. 1.1 The system consists of a Waters 2690 Alliance pump (in diagram 2), a Waters 515 pump (1), a Waters 996 photodiode array detector (7) , six-way switch tap (4), large volume injection device (holds up to 5.0 ml of sample) (3) and columns (5,6). The concentrating column was Waters Xterra™ RP 18(5 µm, 20 x 3.9 mm), Waters Xterra™ RP analytical column 18(5 µm, 150 x 3.9 mm). pH was determined with a Beckman F-200 pH meter, and optical density was measured with a Shimadzu UV-2401 spectrophotometer.

Fig 1.1Schematic of a real-time concentration system using a switch tap

All solutions were prepared using ultrapure water obtained using the Milli-Q50 Sp Reagent Water System (Millipore Corporation). A standard solution of lead (P) with a concentration of 1.0 mg/ml, working solutions with an ion concentration of 0.2 μg/ml are prepared by diluting standard ones. Use tetrahydrofuran (THF) for HPLC (Fisher Corporation), pyrrolidine-acetic acid buffer solution with a concentration of 0.05 mol/L. Before use, glassware was soaked for a long time in a 5% nitric acid solution and washed with clean water.

Experimental technique. The required volume of a standard solution or sample is added to a 25 cm volumetric flask. 3, add 6 ml of solution T 4CPP with a concentration of 1 x10 -4mol/l in THF and 4 ml of pyrrolidine-acetic acid buffer solution with a concentration of 1 x10 -4mol/l and pH 10, dilute to the mark with water and mix thoroughly. The mixture is heated in a boiling water bath for 10 minutes. After cooling, dilute to the THF mark for subsequent analysis. The solution (5.0 ml) is introduced into the dispenser and sent to a concentrating column using mobile phase A at a rate of 2 cm3/min. Upon completion of concentration by eliminating the six-way valve, metal chelates with T 4CPPs adsorbed at the top of the concentrating column are eluted with a flow of mobile phases A and B at a rate of 1 ml/min in the opposite direction and sent to the analytical column. The three-dimensional chromatogram was recorded in the wavelength range of maximum absorption 465 nm using a detector with a photodiode array.

1.4.3 Stripping voltammetric determination of lead using a glassy carbon electrode system

Instruments and reagents.For the studies, we used an electrode system, which was an assembly of three identical glassy carbon (GC) electrodes (indicator, auxiliary, comparison) pressed into a common tetrafluoroethylene body. The length of each electrode protruding from the housing is 5 mm. The surface of one of them, chosen as an indicator, was electrochemically treated with an asymmetric current at densities in the range of 0.1-5 kA/m 2recommended for metals. The optimal surface renewal time was found experimentally and was 10-20 s. The indicator electrode served as the anode, and the stainless steel electrode served as the cathode. We used 0.1 M aqueous solutions of acids, salts, alkalis, as well as 0.1 M solutions of alkalis or salts in a mixture of organic solvents with water in a ratio of 1: 19 by volume. The condition of the treated surface was observed visually using a Neophot 21 microscope with an increase of about 3000.

Method of analysis.After processing, the electrode assembly was used to determine 3*10 -6M lead (II) by stripping voltammetry against a background of 1*10 -3M HNO 3. After electrolysis at – 1.5 V for 3 min with stirring with a magnetic stirrer, a voltammogram was recorded on a PA-2 polarograph. The potential of the lead anodic peak remained constant and amounted to - 0.7 V. The linear potential scan rate was 20 mV/s, the scan amplitude was 1.5 V, the current sensitivity was 2 * 10-7 A/mm.

Aqueous solutions of LiNO 3, NaNO 3, KNO 3as a processing electrolyte, they allow one to obtain stable heights already in the second measurement with satisfactory reproducibility (2.0, 2.9 and 5.4%, respectively). The greatest sensitivity of readings is achieved when using an electrolyte having a smaller cation.

1.4.4 Atomic absorption determination of lead by dosing suspensions of carbonized samples using Pd-containing activated carbon as a modifier

Analytical measurements were carried out on a SpectrAA-800 atomic absorption spectrometer with a GTA-100 electrothermal atomizer and a PSD-97 autosampler (Varian, Australia). We used graphite tubes with pyrolytic coating and an integrated platform (Varian, Germany), hollow cathode lamps for lead (Hitachi, Japan) and cadmium (Varian, Australia). Integral absorption measurements with correction for nonselective light absorption (deuterium system) were carried out at a spectral slit width of 0.5 nm and a wavelength of 283.3 nm. Argon "highest grade" served as a shielding gas. The temperature program for the atomizer operation is given in Table 1.1

Table 1.1 Temperature program for the operation of the electrothermal atomizer GTA-100

StageTemperature,°CDrying 190Drying 2120Pyrolysis1300Cooling50Atomization23OOCleaning2500

Palladium-containing compositions based on activated carbon and carbonized hazelnut shells were studied as modifiers for the atomic absorption determination of Pb in a graphite furnace. The metal content in them was 0.5-4%. To assess the changes occurring with the components of the synthesized modifiers under reducing conditions implemented during the analysis, the materials were treated with hydrogen at room temperature.

A solution with a known concentration of Pb was prepared by diluting GSO No. 7778-2000 and No. 7773-2000 with 3% HNO 3. The concentration range of working standard solutions of the element for constructing calibration dependencies was 5.0-100 ng/ml. Deionized water was used to prepare solutions .

When constructing pyrolysis and atomization curves, we used both a standard solution of the element and a carbonized “Standard sample of the composition of ground wheat grain ZPM-01”. In the first case, 1.5 ml of a standard solution of the element (50 ng/ml Pd in 5% HNO 3) and 10-12 mg of palladium-containing activated carbon; the suspension was homogenized and dosed into a graphite furnace. In the second, the same amount of modifier was added to the prepared suspension of carbonized sample (5-10 mg of sample in 1-2 ml of 5% HNO3 ).

1.4.5 Photometric determination and concentration of lead

Lead acetate of analytical grade was used in this work. The compounds (Fig. 1, which are dibasic acids) were obtained by azo coupling of a solution of 2-hydroxy-4 (5) - nitrophenyldiazonium chloride and the corresponding hydrazone. Solutions of formazans in ethanol were prepared by precise weighing.

The optical density of solutions was measured on a Beckman UV-5270 spectrophotometer in quartz cuvettes (l = 1 cm). The concentration of hydrogen ions was measured using an I-120M ion meter.

The reagents react with lead ions, forming colored compounds. The bathochromic effect during complex formation is 175 - 270 nm. Complexation is influenced by the nature of the solvent and the structure of the reagents (Fig. 1).

The optimal conditions for the determination of lead are a water-ethanol medium (1:

) and pH 5.5-6.0, created by an ammonium acetate buffer solution. The detection limit for lead is 0.16 µg/ml. Analysis duration 5 min.

The most interesting is the use of formazan as a reagent for the concentration and subsequent photometric determination of lead. The essence of the concentration and subsequent determination of lead (II) using formazan is that the lead complex is extracted from a water-ethanol solution in the presence of Ni, Zn, Hg, Co, Cd, Cr, Fe ions with a chloroform solution of formazan.

For comparison, we used the method for determining lead with sulfarsazen (GOST, MU issue 15, No. 2013-79). The results of the analysis of model solutions using two methods are given in Table 1.2 Comparison of variances using the F-criterion showed that Fexp< Fтеор (R= 0.95; f 1=f 2= 5); This means that the variances are homogeneous.

Table 1.2 results of determination of lead in model solutions (n=6; P=0.95)

Introduced, µg/mlFoundFoundFexpF theorsulfarsazen, µg/mlS r formazan, µg/mlS r 4.14 2.10 3.994.04 ±0.28 2.06±0.29 3.92 ±0.17 0.29 3.92 ±0.172.8 5.5 1.74.14 ±0.07 2.10 ±0.08 3.99 ± 0.072.1 *10 -2 2.5*10-2 2.1*10-23.97 3.57 3.374.53

2. Experimental part

Measuring instruments, reagents and materials:

When performing this method, the following measuring instruments, devices, reagents and materials are used:

· Atomic absorption spectrometer

· Spectral lamp with hollow cathode

· Compressor for supplying compressed air

· Gearbox - according to GOST 2405

· Laboratory beakers, capacity 25-50 cm3 - according to GOST 25336

· Measuring flasks of the second accuracy class with a capacity of 25-100 cm3

· Laboratory funnels according to GOST 25336

· Distilled water

· Concentrated nitric acid, x. h., GOST 4461-77

· Standard lead solution (c = 10-1 g/l)

Determination conditions:

§ Wavelength when determining lead? =283.3 nm

§ Monochromator slit width 0.1 nm

§ Lamp current 10 mA

Method of measurement:

Atomic absorption spectroscopy is based on the absorption of radiation in the optical range by unexcited free lead atoms formed when the analyzed sample is introduced into a flame at a wavelength ? =283.3 nm.

Safety requirements:

When performing all operations, it is necessary to strictly observe the safety rules when working in a chemical laboratory, corresponding to GOST 126-77 "Basic safety rules in a chemical laboratory", including rules for safe work with electrical devices with voltages up to 1000 volts.

Preparation of lead calibration solutions:

Solutions are prepared using a standard lead solution with a concentration

c= 10-1 g/l.

To construct a calibration curve, use solutions of the following concentrations:

*10-4, 3*10-4, 5*10-4, 7*10-4, 10*10-4g/l

Standard solution with a volume of 10 cm 3add to a 100 ml flask and fill to the mark with distilled water. In 5 volumetric flasks with a capacity of 100 ml add 1, 3, 5, 7, 10 ml of intermediate solution (solution of concentration 10 -2g/l). Make up to the mark with distilled water. Construct a gradation graph in coordinates A, y. e from s, g/l

Table 2.1 Measurement results

concentration, g/lSignal, u. e. 0.000130.0003150.0005280.0007390.001057

Sample preparation:

I take a sample of coffee weighing 1.9975 g.

I add it to a 100 ml glass.

I dissolve the sample in 20 ml of concentrated nitric acid.

I evaporate the contents of the glass in a water bath to half the original volume, stirring occasionally.

The solution in the beaker after evaporation is cloudy, therefore, using a laboratory funnel and a paper filter, I filter the contents of the beaker into a 25 ml beaker.

I add the filtered solution into a 25 ml flask and bring it to the mark with distilled water.

I thoroughly mix the contents of the flask.

I add part of the solution from the flask into a pipette, which serves as a sample to determine the lead content.

To determine an unknown concentration, the solution is introduced into the atomizer and after 10-15 seconds the readings of the device are recorded. The average readings of the device are plotted on the ordinate axis of the calibration graph, and the corresponding concentration value, сх g/l, is found on the abscissa axis

To calculate the concentration in the sample, I use the calculation formula:

С =0.025*Сх*10-4*1000/ Мnav (kg)

Table 2.2 Measurement results

ProbaSignal, u. e. AverageC X , g/l 123 coffee15141514,666672.9*10 -4cheese00000apples juice00000grape juice00000cream3222.333337.8*10 -5water00000shampoo00000

Based on the tabular data, I calculate the concentration of lead in the samples:

Sample MPC, mg/kg coffee 10 cream

C (Pb in coffee sample) = 3.6 mg/kg

C (Pb in cream sample) = 0.98 mg/kg

conclusions

The work describes methods for determining lead using various physical and chemical methods.

Sample preparation methods for a number of food objects are presented.

Based on literature data, the most convenient and optimal method for determining lead in various food products and natural objects was selected.

The method used is characterized by high sensitivity and accuracy, along with the absence of a response to the presence of other elements, which allows one to obtain true values of the content of the desired element with a high degree of reliability.

The chosen method also makes it possible to conduct research without any particular difficulties in sample preparation and does not require masking of other elements. In addition, the method allows you to determine the content of other elements in the test sample.

Based on the experimental part, we can conclude that the lead content in Black Card coffee does not exceed the maximum permissible concentration, therefore the product is suitable for sale.

List of used literature

1. Glinka N.I. General chemistry. - M.: Nauka, 1978. - 403 p.

Zolotov Yu.A. Fundamentals of analytical chemistry. - M.: Higher. school; 2002. - 494 p.

Remi G. General chemistry course. - M: Ed. foreign lit., 1963. - 587 p.

GOST No. 30178 - 96

Yiping Hang. // Journal. analyte khim., 2003, T.58, No. 11, p.1172

Liang Wang. // Journal. analyte khim., 2003, T.58, No. 11, p.1177

Nevostruev V.A. // Journal. analyte khim., 2000, T.55, No. 1, p.79

Burilin M.Yu. // Journal. analyte khim., 2004, T.61, No. 1, p.43

Maslakova T.I. // Journal. analyte khim., 1997, T.52, No. 9, p.931

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    What is valuable in your articles is your personal attitude and analysis of the topic. Don't give up this blog, I come here often. There should be a lot of us like that. Email me I recently received an email with an offer that they would teach me how to trade on Amazon and eBay. And I remembered your detailed articles about these trades. area I re-read everything again and concluded that the courses are a scam. I haven't bought anything on eBay yet. I am not from Russia, but from Kazakhstan (Almaty). But we also don’t need any extra expenses yet. I wish you good luck and stay safe in Asia.
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It’s also nice that eBay’s attempts to Russify the interface for users from Russia and the CIS countries have begun to bear fruit. After all, the overwhelming majority of citizens of the countries of the former USSR do not have strong knowledge of foreign languages. No more than 5% of the population speak English. There are more among young people. Therefore, at least the interface is in Russian - this is a big help for online shopping on this trading platform. eBay did not follow the path of its Chinese counterpart Aliexpress, where a machine (very clumsy and incomprehensible, sometimes causing laughter) translation of product descriptions is performed. I hope that at a more advanced stage of development of artificial intelligence, high-quality machine translation from any language to any in a matter of seconds will become a reality. So far we have this (the profile of one of the sellers on eBay with a Russian interface, but an English description):
https://uploads.disquscdn.com/images/7a52c9a89108b922159a4fad35de0ab0bee0c8804b9731f56d8a1dc659655d60.png

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