Determination of organic substances in water. Determination of lead in urban vegetation Qualitative analysis of lead content in biological material

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Course work

Determination of lead in the vegetation of an urban area

Introduction

lead titrimetric metal reagent

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

It is estimated that exposure to lead in childhood is one of the factors causing about 600,000 new cases of development of mental disorders in children every year.

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

In the body, lead enters the brain, liver, kidneys, and bones. Over time, lead accumulates in teeth and bones. Exposure in humans is usually determined by measuring lead levels in the blood.

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

The main sources of lead pollution are road transport using lead-containing gasoline, metallurgical plants, smoke sources such as thermal power plants and others.

Plants absorb lead from soil and air.

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

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

In this term paper the content of lead in the vegetation of the urban area is being studied.

1. Leeliterature review

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

1. 1 Aboutgeneral information about lead

Lead (lat. Plumbum; denoted by the symbol Pb) - an element of the 14th group (an outdated classification - the main subgroup of group IV), the sixth periodic system chemical elements D.I. Mendeleev, with atomic number 82 and thus contains the magic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 low-melting 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, however, its fluctuations by 0.03 - 0.04 u.h. are possible.

Lead is integral part 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).

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

To get lead highest value have polymetallic sulfide and mixed ores, since pure lead ores are rare.

It is applied for the purpose radiation protection, as structural material in the chemical industry, for the manufacture of protective coatings for electric cables and battery electrodes. Large amounts of lead are used to manufacture various alloys: with bismuth (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 anti-friction purposes). The ability to form intermetallic compounds is used to obtain lead telluride, from which detectors of infrared rays and converters of thermal radiation energy into electrical energy are prepared. A large proportion of lead is used for the synthesis of organometallic compounds.

Many lead-containing organic compounds are products of "small" 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 chlorosulfo polyethylene), lead diamildithiocarbamate (multifunctional lubricating oil additive), ethylenediaminetetraacetate lead (radiocontrast agent), lead tetraacetate (oxidizer in organic chemistry). Of the practically important inorganic compounds, one can name lead oxide (which is used in the production of glasses with a high refractive index, enamels, batteries and high-temperature lubricants); lead chloride (manufacturing of current sources); basic carbonate, sulfate and chromate of lead, minium (components of paints); titanate - zirconate. lead (production of piezoelectric ceramics). Lead nitrate is used as a titrant.

The exceptional diversity and importance of the mentioned fields of application of lead 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 of Pb. The cosmic abundance of this element, according to the data of various authors, varies from 0.47 to 2.9 atoms per 106 silicon atoms. For 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-micro quantities - in almost all objects of the surrounding world.

Other objects contain lead (% mass); rain water - (6-29) * 10 -27, water open sources- 2 * 10 -8, sea waters - 1.3 waters of the open ocean 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. The total lead content (in tons): in the atmosphere - 1.8 * 10 4, in soils - 4.8 * 10 9, in sedimentary deposits - 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 organisms of water and land: living - 8.4 * 10 4, dead - 4.6 * 10 6.

1.2 Islead pollution sources

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 (lead production 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 trace elements.

A significant part of the lead contained in coal, when burned, together with flue gases, enters the atmosphere. The activity of only one thermal power plant, which consumes 5000 tons of coal per day, annually sends 21 tons of lead and commensurate amounts of other harmful elements into the air. A considerable contribution to the air pollution with lead is made by 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 reaches even the stratosphere. The resulting lead is partially returned to the ground 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. He and his compounds are dangerous not only because of the pathogenic effect, but also because of the cumulative therapeutic effect, the high coefficient of accumulation in the body, the low rate and incomplete excretion with waste products. Facts about the dangers of lead:

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 respect.

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 in workers with lead.

5. According to the results of 10 years of statistics, a correlation has been established between the number of deaths from lung cancer and an increased content of lead and other metals in the air of regions industrial enterprises consuming coal and oil products.

The degree of toxicity depends on the concentration, physicochemical state and nature of the lead compounds. Lead is especially dangerous in the state of molecular-ion dispersity; it penetrates from the lungs into the circulatory system and from there is transported throughout the body. Although the quality of lead and its inorganic compounds act similarly, toxicity increases symbatically with their solubility in body fluids. This does not diminish the danger of sparingly 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 disturbed, the immunobiological properties of the organism 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 compounds, preference is given to lead sulfate and chromate. Methods based on their precipitation are comparable in selectivity and the value of the conversion factor, but the determination of Pb in the form of chromate requires less time. Both precipitates are recommended to be obtained by "homogeneous" precipitation methods.

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

Advantages of the method: precipitate crystallinity 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 alkali metals and ammonium should be as small as possible.

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 are most convenient with indication of the end point of titration (CTT) by changing the color of methyl red or adsorption indicators. 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 dissolution of the precipitate in 2 M HC1 or 2 M HC10 4, the addition of an excess of potassium iodide and titration of the released iodine Na 2 S 2 0 3.

3. Titration with EDTA solutions. In view of 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 \u003e 3. Usually, they are titrated 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 dihydric phenols and some other substances, the colored Pb complexes of which are less stable than lead ethylenediaminetetraacetate. In weakly acidic media, titrate with 4 - (2-pyridylazo) - resorcinol, thiazolyl-azo-and-cresol, 2 - (5-bromo-2-pyridylazo) - 5-diethylaminophenol, 1 - (2-pyridylazo) - 2-naphthol , 2 - (2-thiazolilazo) - resorcinol, azo derivatives of 1-naphthol4-sulfonic acid, xylenol orange, pyrocatechin violet, methylxylenol blue, pyrogallol and bromopyrogallol red, methylthymol blue, hematoxylin, sodium rodizonate, alizarin S and dithizone.

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

4. Titration with other complexing substances. The formation of chelates with DTCA, TTGA, sulfur-containing complexing substances 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 appraisal date back to the beginning of our 20th century. The color and stability of the PbS sol depend on the particle size of the dispersed phase, which is affected by the nature and concentration of dissolved electrolytes, the reaction of the medium, and the method of preparation. 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 the determination is less, but it can be somewhat increased by adding electrolytes, such as 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 solution of HC1, 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 from 4-10*10-4%.

3. The determination of Pb impurities in concentrated sulfuric acid is based on the use of the characteristic absorbance at 195 nm with respect to a standard solution prepared by dissolving lead in H2SO4 (high purity).

Determination using organic reagents.

4. In the analysis of various natural and industrial objects, the photometric determination of Pb using dithizone occupies a leading position due to its high sensitivity and selectivity. IN various options existing methods, the photometric determination of Pb is performed at the maximum absorption wavelength of dithizone or lead dithizonate. Other versions 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 to a concentration of the organic component of 70% before use.

5. Determination of lead by reaction with sodium diethyldithiocarbamate. Lead is well extracted with CCl4 as a colorless diethyldithiocarbamate at various pH values. The resulting extract is used in an indirect method for determining Pb, based on the formation of an equivalent amount of yellow-brown copper diethyldithiocarbamate as a result of exchange with CuSO4.

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, such as steel, brass and bronze, the method based on the formation of a complex with this azo compound is preferable to the dithizone method. However, it is less selective and, therefore, in the presence of interfering cations, it requires preliminary separation by the BC 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 with a composition of 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 of 4-8 forms a blue complex with lead in the composition 1:1 with two absorption maxima - at 605 and 665 nm.

10. Determination by reaction with diphenylcarbazone. According to the sensitivity of the reaction, during the extraction of 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% HCl, and the photometric determination of dichromic acid by reaction with diphenylcarbazide using a filter with a maximum transmission at 536 nm. The method is lengthy 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 a 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 at pH 6.5, and cetyltrimethylammonium and cetylpyridinium bromides at pH 5.0.

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

15. Determination with methylthymol blue is carried out under conditions as for the formation of a complex with GTS. In sensitivity, both reactions approach 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 ratio is 19,500. Interference from many metals is eliminated by masking.

16. Determination by reaction with EDTA. EDTA is used as a titrant in non-indicator and indicator photometric titration (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 is proposed in which the intensity of chemiluminescence emission in the presence of Pb is measured 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, traces of copper catalyze the luminol oxidation reaction. A method based on the use of the fluorescence quenching effect of fluores-132 derivatives is much more difficult in terms of instrumentation 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 water-blue lumogen in a mixture of dioxane-water (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 the determination of lead in HC1, based on the photoelectric detection of green fluorescence of chloride complexes at -70°C.

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

4. A method is proposed based on measuring the analytical signal at 365 nm in the quasi-linear 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 tablet surface (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. Simultaneously with Pb, Bi can also be determined.

5. Determination of lead by the luminescence of the chloride complex adsorbed on paper. In this method, luminescence 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. Used direct and indirect definition lead - by titration with acid - basic, complexometric and precipitation reagents.

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

3. Coulometry and coulometric titration. Electrogenerated sulfohydryl 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 10–10 M. proceeding reversibly and in the diffusion mode. As a rule, cathodic waves are well pronounced, 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 electrochemical conversion current Pb and (or) titrant at a certain value of the electrode potential on the volume of the titrant. Amperometric titration is more accurate than the conventional polarographic method, does not require mandatory temperature control of the cell, and to a lesser extent depends on the characteristics of the capillary and the indifferent electrolyte. The great possibilities of the AT method should also be noted, since analysis is possible by an electrochemical reaction involving both Pb itself and the titrant. Although the overall time spent on performing an AT is longer, it is quite 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 uc (benzylidene) - thio - carbohydrazone, thiosalicylamide.

1.7 fiPhysical methods for the determination of lead

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

2 . experimentalPart

2.1 Medefinition method

The work uses the definition of lead in the form of a dithizonate complex.

Figure 1 - structure of dithizone:

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

Double incineration 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 has high accuracy.

2. 2 Etcborons and reagents

Spectrophotometer with cuvettes.

Drying cabinet.

Muffle furnace.

Electric stove.

Electronic balance

Dropping funnel 100 ml.

Chemical vessels.

A sample 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% ammonium citrate solution.

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 in-va /m p-ra =0.1%. The mass of the solution is 100 gr. Then the sample is 0.1 gr. Dissolved in 99.9 ml of bidistilled water.

2.10% solution of yellow blood salt. W \u003d m in-va / m p-ra \u003d 10%. The mass of the solution is 100 gr. Then the sample is 10 gr. Dissolved in 90 ml of bidistilled water.

3.10% ammonium citrate solution. W \u003d m in-va / m p-ra \u003d 10%. The mass of the solution is 100 gr. Hanging - 10 gr. Dissolved in 90 ml of bidistilled water.

4.10% HCl solution. Made from concentrated HCl:

You need 100 ml of a 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 bidistilled water in a 100 ml volumetric flask to the mark.

5. 0.01% solution of dithizone in CCl 4 . W \u003d m in-va / m p-ra \u003d 10%. The mass of the solution is 100 gr. Then the sample is 0.01 gr. Dissolved in 99.9 ml CCl 4 .

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

7. 0.02 N HCl solution. W \u003d m in-va / m r-ra \u003d? 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, it is necessary to take 1.92 g of concentrated HCl, volume = 1.61 ml. 1.61 ml of concentrated HCl was diluted to 100 ml with bidistilled water in a 100 ml volumetric flask to the mark.

9. Thymol blue indicator solution was prepared from dry matter by dissolving in ethyl alcohol.

2. 4 Medisturbing influences

In an alkaline medium containing cyanide, thallium, bismuth and tin (II) are extracted with dithizone together with lead. Thallium does not interfere with colorimetric determination. Tin and bismuth are removed by extraction in an acid 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 they are present in a fifty-fold concentration, is eliminated by double extraction.

The determination is hindered by manganese, which, when extracted in an alkaline medium, catalytically accelerates the oxidation of dithizone with atmospheric oxygen. This interfering influence is eliminated by adding hydrochloric acid hydroxylamine to the extracted sample.

Strong oxidizing agents interfere with the determination, as they oxidize dithizone. Their reduction with hydroxylamine is included in the course of the determination.

2. 5 ThoseExperimental technique

The plant material was dried in an 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 samples of dry material, 10 g each, 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.

After that, the ashes of the plants were dipped in nitric acid when heated and dried (henceforth, 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.

After the clarified ash dug in hydrochloric acid, dried, and dug in again. Then the samples were dissolved in 10 ml of 10% hydrochloric acid.

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

This was followed by extraction. Was poured 5 ml of a 0.01% solution of dithizone in CCl 4 . The solution in the dropping funnel was vigorously shaken for 5 minutes. The dithizone layer after its separation from the main solution was drained separately. The extraction operation was repeated until the initial color of each new portion of dithizone ceased to turn red.

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

Then the solutions were neutralized with a soda solution until the color of the indicator (phenol red) changed to 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 spectophotometrically measured against a solution of dithizone in CCl 4 at 520 nm.

The following optical densities were obtained:

The calibration graph was built under the same conditions, standard solutions of lead concentrations from 1 to 6 µg/ml were used. They were prepared from a 1 µg/mL lead solution.

2.6 Reexperimental resultsdata and statistical processing

Data for building a calibration graph

Calibration curve

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

1) 0.71 mg/kg

2) 0.71 mg/kg

3) 0.70 mg/kg

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

Average value of the mass: X cf = 0.707 gr.

Dispersion =0.000035

Standard deviation: = 0.005787

Youwater

1. According to the literature review.

With the help of a literature review, general information about the element, its methods of determination, the most suitable of them is selected according to its accuracy and compliance with those used in everyday practice.

2. According to the results of the experiment.

The experiment showed that using the method it is possible to determine the low content of lead, the results are highly accurate and convergent.

3. In accordance with MPC.

List of used literary sources

1. Polyansky N.G. Lead.-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: Proc. For chemical-technological Specialist. Universities.-M.: Higher. school, 1989. - 384 p.

3. Basics analytical chemistry. In 2 books. Book. 2. Methods of chemical analysis: Proc. For universities / Yu.A. Zolotov, E.N. Dorohova, V.I. Fadeev and others. Ed. Yu.A. Zolotova. - 2nd ed., revised. And extra. - M.: Higher. school, 2002. - 494 p.

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conclusions

The systematic method of hydrogen sulfide analysis of metal and arsenic cations currently used in forensic practice is outdated.
The fractional method for the analysis of metal cations and arsenic, which is 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 for the detection of metals and arsenic, and also significantly reduce the consumption of reagents and abandon the use of hydrogen sulfide, which pollutes the air of laboratories.

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

After the mineralization of organs with sulfuric and nitric acids, lead and barium will be in the sediment in the form of BaSO 4 and PbS0 4 . The optimal conditions for quantitative precipitation

of Ba 2 + and Pb 2 + are: the concentration of H 2 SO 4 in the mineralization ~ 20% H 2 SO 4, the absence of nitrogen oxides (partial dissolution of PbSO 4 and, to a much lesser extent, BaS0 4 in nitric acid), time precipitation (~24 hours). Due to co-precipitation, Ca 2 +, Fe 3+, Al 3 +, Cr 3+, Zn 2+, Cu 2+, etc. can also be in the precipitate. When co-precipitating Cr 3 +, the precipitate is colored dirty green. To avoid loss of Cr 3+, the dirty green precipitate is treated with a solution of ammonium persulfate in 1°/o sulfuric acid solution while heated. The undissolved precipitate is analyzed for Ba 2 + and Pb 2 +, and the filtrate is left for the quantitative determination of chromium. In order to separate Ba 2+ and Pb 2+ (the presence of Pb 2 + interferes with the detection of Ba 2 +), the precipitate directly on the filter is carefully treated with 0.5-10 ml (depending on the size of the precipitate) of a hot solution of ammonium acetate 1, achieving completeness dissolving PbSO 4 ;

Qualitative detection

The filtrate is examined for lead: a) reaction with dithizone (НrDz)

Dithizone (diphenylthiocarbazone) has found wide application in inorganic analysis. Depending on the pH of the medium in solutions, dithizone can exist in two forms:

In the enol form, the reagent is slightly soluble in organic solvents (chloroform, carbon tetrachloride). In the ketonnon form, oi dissolves quite well in them, forming intensely colored green color solutions. In alkaline solutions it gives an anion HDz", which is colored orange.

With many metal cations [Mn, Cr, Co, Ni, Zn, Fe(III), Tl, Cu, Cd, Ag, Pb, Bi, Hg], dithizone gives intracomplex salts (ditizonates), which are usually soluble in nonpolar organic compounds. sk solvents (CHC1 3, CC1 4). Many of the intracomplex compounds are brightly colored.

and secondary dithizonates:

There are primary dithizonates:

Primary dithizonates form with all cations. Secondary dithizonates are formed with only a few metals (HgDz, Ag 2 Dz, CuDz, etc.). Fischer, who introduced dithizone into analytical practice (1957), attributes the following structure to them:

Where a metal can give both primary and secondary dithizonate, it all depends on the reaction of the pH of the medium: in an acidic medium, primary dithizonate is formed, in an alkaline medium and with a lack of a reagent, secondary dithizonate is formed.

Both the formation and extraction of dithizonates depend primarily on the pH of the medium.

To detect lead, the solution obtained by treating the precipitate of PbS0 4 and BaS0 4 with ammonium acetate is shaken with a solution of dithizone in chloroform (CC1 4): in the presence of Pb 2 +, it is observed (at pH 7.0-10.0) "appearance purplish red color

The reaction is highly sensitive - 0.05 μg R 2+ in 1 ml. The limit of detection of Pb 2+ by this reaction in the organs is 0.02 mg.

Under the described conditions of chemical-toxicological analysis, the reaction is almost absolutely specific, since the production of Pb(HDz) 2 is preceded by the conversion of Pb 2+ to PbSO 4, i.e., the separation of Pb 2+ from most other elements. With PbSO 4, mainly Fe 3 + and Cr 3 + can coprecipitate. At the same time, Fe 3+ has a low affinity for dithizone, and Cr 3 + forms uncolored compounds with dithizone.

One of the advantages of the reaction is the ability to combine with its help a qualitative analysis for Pb 2+ with a quantitative determination. In this case, in the presence of a purple-red color of the chloroform layer, first

quantitative determination (see p. 302). Then, after measuring the color density of Pb (HDz) 2 on a photoelectrocolorimeter, lead dithizonate for further qualitative reactions is vigorously shaken for 60 seconds with 0.5-2 ml (depending on the volume and color intensity of the extract) 1 n. HNO 3 solution (or HC1):

Pb(HDz) 2 >- Pb(N0 8) 2 + 2H 2 Dz

(organic layer (water (organic layer)

calcic solution layer) calcic

bearer) creator)

Depending on the volume of the aqueous layer, the solution is further investigated by microcrystalline or macrochemical reactions.

I. With a small volume of the aqueous layer (0.5 ml), the entire volume is divided into 2 parts, carefully evaporated and reactions are carried out: a) a double salt of cesium iodide and c in and n c a - CsPbl 3 are obtained. Acidify 1/2 part of the residue with 30% acetic acid and mix with several crystals of potassium iodide:

1-2 crystals of cesium chloride are added to the solution - after some time a greenish-yellow precipitate of cesium iodide and lead precipitates. When viewed under a microscope, one can observe needle-shaped crystals, often collected in beams and spheroids.

Optimal conditions: 30°/v acetic acid solution, no mineral acids, little CsCl and excess KI.

The sensitivity of the reaction is 0.01 μg. The reaction makes it possible to detect (detection limit) 0.015 mg Pb 2+ per 100 g of the object of study;

b) formation of potassium, copper and lead hexanitrite КrСuРb(NO 2) 6 . The second part of the residue is mixed with 1-2 drops of a saturated solution of copper acetate and carefully evaporated to dryness. The residue is dissolved in 2-3 drops of a 30% solution of acetic acid and a few crystals of potassium nitrite are added. In the presence of Pb 2+, after 5-10 minutes, KrCu Pb(NO 2) 6 crystals appear in the form of black or brown (with small amounts of Pb 2 +) cubes over the entire field of view. Optimal conditions: 30% solution of CH 3 COOH, absence of mineral acids, excess of potassium nitrite. The sensitivity of the reaction is 0.03 μg. The detection limit for Pb 2+ in biological material is 0.015 mg per 100 g of the organ.

P. When large volume of the aqueous layer (2 ml or more), it is neutralized to pH 5.0 according to universal indicator paper, divided into 4 parts and examined by the reactions:

a) formation of PbS:

Pb(N0 3) 2 + H 2 S = PbSJ + 2HN0 3 .

The precipitate does not dissolve in dilute sulfuric and hydrochloric acids, but dissolves in dilute nitric acid with the release of nitrogen oxides and elemental sulfur:

3PbS + 8HNO 3 \u003d 3Pb (NO 3) 2 + 2NO + 3S + 4H 2 O;

b) formation of PbS0 4:

Pb(OCOCH 3) 2 + H 2 SO 4 = PbSO 4 | + 2CH 3 COOH

Lead sulfate is slightly soluble in water (1:22,800 at 15°); in dilute sulfuric acid, its solubility is even less; it is practically insoluble in alcohol; dissolves significantly in nitric acid, even better - in hydrochloric acid, especially when heated:

When water is added, lead sulfate precipitates again.

The precipitate of lead sulfate dissolves in solutions of caustic soda, caustic potash, acetate and ammonium tartrate (difference from barium sulfate and strontium sulfate):

When dissolved in ammonium tartrate, Pb 2 0 (C 4 H 4 0 6) 2 is formed.

c) formation of PbCr0 4 ; insoluble in acetic acid, but
soluble in mineral acids and caustic alkalis:

2Pb (OSOCH 3) 3 + K 2 Cr 2 0 7 + HOH - 2CH 3 COOK + 2PSYU 4 + 2CH 3 COOH.

d) the fourth part is examined by microchemical reactions
obtaining CsPbl 3 and K2CuPb(N0 2)e.

Quantitative determination of Pb 2+ after its isolation in the form of lead sulfate is possible by several methods:

a) bichromate o-th odometric in excess of bichromate that did not react with Pb 2+. The definition is based on the following reactions:

The bichromate-iodometric method of determination gives good results (93% with an average relative error of 1.4 ° / o) with a content of 2 to 100 mg of lead per 100 g of the organ. With lead amounts less than 2 mg (determination limit), the method is unreliable. For example, in the presence of 1 mg of Pb 2 + in 100 g of an organ, only 37% is determined on average;

b) extraction-photometric metric and under lead diti-zonate. The method is based on the above sensitive and rather specific reaction:

Pb (OSOCH 3) 2 4- 2H a Dz (at pY 7-10) - Pb (HDz) a + 2CH 3 COOH.

The resulting dithizonate is extracted with chloroform at a pH above 7.0 until the extraction of Pb 2+ is complete. The extracts are combined, washed with a KCN solution in the presence of NH 4 OH, settled, the volume is measured, and then the color density of the chloroform extract is determined on FEC at a full length of 520 nm in a cuvette with an absorbing layer thickness of 1 cm. Chloroform serves as a reference solution. Beer's law is observed within 0.0001 - 0.005 mg / ml.

c) complexometric, which is common to many divalent and some trivalent cations.

The principle of complexometric titration boils down to the following: a small amount of the corresponding indicator is added to the test solution containing a certain cation at a strictly defined pH value - a colored complex compound of the indicator with the cation, which is highly soluble in water, is formed. When titrated with trilon B (complete III) - disodium salt of ethylenediaminetetraacetic acid, the complex of the cation with the indicator is destroyed, since trilon B forms a more stable complex with the cation being determined. At the equivalent point, a free indicator is released, coloring the solution in the color inherent in the indicator at a given pH value of the medium.

Most cations are determined in an alkaline medium, for which an ammonia buffer (a mixture of ammonia and ammonium chloride) is introduced into the titrated solution.

The determination of Pb 2+ (or another divalent cation) is based on the following reactions:

A. N. Krylova for the determination of Pb 2+ recommends back titration of Trilon B (used to determine cations that react with a solution of NH 4 OH). The essence of the technique is as follows: the test solution is diluted with water to 100-150 ml and mixed with an excess of 0.01 N. solution of Trilon B. 10 ml of ammonia-chloride buffer 2 and 0.1 - 0.2 g of dry Zriochrome black T (mixture with NaCl 1:200). An excess of Trilon B is titrated with 0.01 N. ZnCl 2 solution until the blue-blue color changes to red-violet. 96% is determined with an average relative error of 6.2% at 1 mg Pb 2 + per 100 g of the organ; 97% with an average relative error of 27% at 10 mg. The limit of determination is 0.5 mg Pb 2 + per 100 g of the organ.

toxicological significance. The toxicological significance of lead is determined by the toxic properties of metallic lead, its salts and some derivatives, their wide and varied use in industry and everyday life.

Especially dangerous in relation to lead poisoning are the extraction of lead ores, lead smelting, the production of batteries, lead paints [white lead 2PbCO 3 .Pb (OH) 2 and red lead Pb 3 O 4], the use of which in the USSR is limited only to painting ships and bridges , tinning, soldering, the use of lead glaze PbSi0 3, etc. With insufficient labor protection, industrial poisoning is possible.

Sources of domestic poisoning were, in a number of cases, poor-quality tinned, enameled, porcelain-faience and glazed earthenware.

Cases of lead poisoning through drinking water (lead pipes), snuff wrapped in lead paper, after a gunshot wound, etc. are described. There are also known cases of poisoning with lead salts and tetraethyl lead.

Lead is a protoplasmic poison, causing changes mainly in the nervous tissue, blood and blood vessels. The toxicity of lead compounds is largely related to their solubility in gastric juice and other body fluids. Chronic lead poisoning produces a characteristic clinical picture. The lethal dose of various lead compounds is not the same. Children are especially sensitive to it. Lead is not a biological element, but is usually present in water and food, from where it enters the body. A person who is not working with lead absorbs, as N.V. Lazarev points out, 0.05-2 g of lead per day (an average of 0.3 mg). Lead compounds can accumulate in bone tissue, liver, and kidneys. About 10% of it is absorbed by the body, the rest is excreted in the feces. Lead is deposited in the liver and in tubular, somewhat less - in flat bones. In other organs, it is deposited in a small amount. Hence the possibility of detecting lead in the internal organs of the corpses of people who died from other causes, and the need to quantify it with positive results of a qualitative analysis.

The natural content of lead (according to A. O. Voinar, in milligrams per 100 g of the organ) in the liver is 0.130; in the kidney 0.027; in tubular bones 1.88; in the stomach and intestines 0.022 and 0.023, respectively.

In the forensic-chemical and chemical-toxicological analysis, in the study of biological material (organs of corpses, biological fluids, plants, food products, etc.), the mineralization method is used for the presence of "metallic" poisons. These poisons in the form of salts, oxides and other compounds, in most cases, enter the body orally, are absorbed into the blood and cause poisoning. "Metal" poisons will be in the body in the form of compounds with proteins, peptides, amino acids and some other substances that play an important role in life processes. The bonds of metals with most of these substances are strong (covalent). Therefore, to study biological material for the presence of "metal" poisons, it is necessary to destroy the organic substances with which metals are associated and transfer them to the ionic state. The choice of the method of mineralization of organic substances depends on the properties of the elements under study, the amount of biological material received for analysis.

Mineralization is the oxidation (burning) of organic matter (object) to release metals from their complexes with proteins and other compounds. The most widely used methods of mineralization can be divided into 2 large groups:

General methods (methods of "wet" mineralization) are used in a general study for a group of "metal poisons", suitable for isolating all metal cations. Besides mercury. For mineralization, mixtures of oxidizing acids are used: sulfuric and nitric, sulfuric, nitric and perchloric.

Private methods (methods of "dry ashing") - a method of simple combustion, a method of fusion with a mixture of nitrates and carbonates of alkali metals. Particular methods include the method of partial mineralization (destruction), which serves to isolate inorganic mercury compounds from biological materials.

1.1. Destruction of biological material by nitric and sulfuric acids

In a Kjeldahl flask with a capacity of 500-800 ml, add 100 g of crushed biological material, add 75 ml of a mixture consisting of equal volumes of concentrated nitric and sulfuric acids and purified water. The flask with the contents in a vertical position is fixed in a stand so that its bottom is above the asbestos mesh at a distance of 1-2 cm. A separating funnel is fixed above the Kjeldahl flask in a stand, which contains concentrated nitric acid diluted with an equal volume of water. Next, begin to gently heat the flask. Within 30-40 minutes, destruction occurs, the destruction of the uniform elements of biological material. At the end of the destruction, a translucent liquid is obtained, colored yellow or brown.

Then the Kjeldahl flask with the contents is lowered onto an asbestos grid and heating is increased - the stage of deep liquid-phase oxidation begins. To destroy the organic substances in the flask, concentrated nitric acid diluted with an equal volume of water is added dropwise from a dropping funnel. Mineralization is considered complete when a clear liquid (mineralizate) ceases to darken when heated without adding nitric acid for 30 minutes, and white vapors of sulfuric anhydride are released above the liquid.

The resulting mineralizate is subjected to denitration: cool, add 10-15 ml of purified water and heat to 110-130°C, and then carefully drop by drop, avoiding excess, add a solution of formaldehyde. At the same time, an abundant release of brown, sometimes orange, vapors is noted. After the release of these vapors, the liquid is still heated for 5-10 minutes, and then 1-2 drops of the cooled liquid (mineralizate) are applied to a glass slide or porcelain plate and a drop of diphenylamine solution in concentrated sulfuric acid is added. The effect of the reaction is a characteristic blue coloration.

The negative reaction of the mineralizate with diphenylamine to nitric, nitrous acids, and also to nitrogen oxides indicates the end of the denitration process. With a positive reaction of the mineralizate with diphenylamine, denitration is repeated.

The method of mineralization of biological material with concentrated nitric and sulfuric acids has a number of advantages. Mineralization by this method is faster, a relatively small amount of mineralizate is obtained than using other methods. However, mineralization with a mixture of sulfuric and nitric acid is unsuitable for isolating mercury from biological material, since a significant amount of it volatilizes when the biological material is heated at the stage of deep liquid-phase oxidation.

LEAD COMPOUNDS

Lead ions that enter the body combine with sulfhydryl and other functional groups of enzymes and some other vital protein compounds. Lead compounds inhibit the synthesis of porphyrin, cause dysfunction of the central and peripheral nervous system. About 90% of lead ions entering the blood are bound by erythrocytes.

Lead compounds are excreted from the body mainly with feces. Smaller amounts of these compounds are excreted in the bile, and traces are excreted in the urine. Lead compounds are partially deposited in bone tissue in the form of trisubstituted phosphate. It should be borne in mind that small amounts of lead are contained in the body as a normal component of cells and tissues.

Examination of mineralizates for the presence of lead

To detect lead in the organs of corpses, blood, urine and other objects of biological origin, a precipitate is used, which is formed in mineralizates after the destruction of biological material by a mixture of sulfuric and nitric acids.

After the destruction of biological material by a mixture of sulfuric and nitric acids, lead precipitates in the mineralizate in the form of a white precipitate of lead sulfate. The same color precipitate of barium sulfate is formed during poisoning with barium compounds. As a result of co-precipitation, precipitates of lead and barium sulfates can be contaminated with calcium, chromium, iron, etc. ions. If chromium is present in the precipitate, it has a dirty green color. To free precipitates of lead and barium sulfates from impurities, these precipitates are washed with sulfuric acid and water, and then the precipitate of lead sulfate is dissolved in an acidified ammonium acetate solution:

The course of analysis for the presence of lead depends on the amount of precipitation in the mineralizates.

Investigation of relatively large precipitates of lead sulfate

Reaction with potassium iodide. In the presence of lead ions, a yellow precipitate of PbI 2 precipitates, which dissolves when heated and reappears as yellow plates when the solution is cooled.

Reaction with potassium chromate. The formation of an orange-yellow precipitate of barium chromate indicates the presence of lead ions in solution. Limit of detection: 2 µg of lead per sample.

Reaction with hydrogen sulfide water. The appearance of a black precipitate of lead sulfide (or turbidity) indicates the presence of lead ions in solution. Limit of detection: 6 µg of lead per sample.

reaction with sulfuric acid. The appearance of a white precipitate indicates the presence of lead ions in the solution. Limit of detection: 0.2 mg lead ions per sample.

TETRAETHYLlead

TES is a clear, colorless liquid with an unpleasant, irritating odor (in negligible concentrations it has a pleasant fruity odor). It is almost insoluble in water, easily soluble in kerosene, gasoline, chloroform.

The isolation of tetraethyl lead is carried out by various methods, depending on the nature of the object.

a) When examining the internal organs of a corpse, isolation is carried out by distillation with water vapor. The distillate in the amount of 50-100 ml is collected in a receiver containing 30 ml of a saturated alcoholic solution of iodine; the receiver is connected to a trap containing also a saturated alcohol solution of iodine.

After distillation, the contents of the trap and the distillate are combined, covered with a watch glass and left for 30 minutes at room temperature, then evaporated to dryness in a porcelain cup on a water bath. The residue is treated with nitric acid (1:2) and again evaporated on a water bath. The crystalline residue is dissolved in a small amount of distilled water and subjected to a qualitative and quantitative study on the lead ion according to the method described above. For the purposes of chemical-toxicological analysis, the method was developed by A. N. Krylova.

Research at TPP should be carried out immediately upon receipt of the object. A positive result is obtained with a content of 0.3 mg of TES in 100 g of the test object.

In case of a negative result in the study at the TPP, it is necessary to analyze the decomposition products of tetraethyl lead - non-volatile lead compounds, for which the contents of the flask after distillation of the TPP are placed in a large porcelain cup and evaporated in a water bath. The residue is subjected to mineralization with sulfuric and nitric acids and examined as described above. A positive result is observed even in the presence of 0.3 mg of inorganic lead in 100 g of cadaveric material.

b) Isolation from plant objects.
In the study of animal products (meat, meatballs, etc.), thermal power plants are isolated according to the method described above. If the products are flour, cereals, bread and other substances of vegetable origin, the isolation of the thermal power plant is
it is more respectful to produce by extraction with an organic solvent. In this case, 50-100 g of the object is poured, for example, with chloroform and left at room temperature for 2 hours in a flask with a ground stopper. The chloroform extract is filtered into a beaker, on the bottom of which about 1 g of dry
crystalline iodine. Stir the contents of the beaker periodically. rotational movement in order to accelerate the dissolution of iodine. The object on the filter is washed 1-2 times with chloroform, and the washing liquid is collected in the same beaker. After 15-30 minutes, the contents of the glass are transferred to a porcelain
cup and evaporated to dryness on a water bath. Dry residue
destroy with sulfuric and nitric acids, remove nitrogen oxides
and examine for Pb 2+ .

When examining clothing for the presence of TES, it is subjected to extraction with an organic solvent with further transfer of TES to inorganic lead compounds, detection and quantitative determination of it.

c) Insulation from gasolines. All methods for isolating TES from gasoline are reduced to the destruction of the tetraethyl lead molecule and the detection and determination of Pb 2 +. Let's take one of the ways as an example. Mix 20 ml
of gasoline with 20 ml of a 4% alcohol solution of iodine. After some time, the aqueous phase is poured into a porcelain dish and evaporated to dryness on a water bath. The resulting residue is examined for Pb 2 +

Qualitative detection and quantification. After the destruction of the TES molecule, the detection and determination of Pb 2+ does not present any special features. All reactions and methods described above are suitable.

Iodometrically, it is possible to determine up to 1 mg of TES in the test sample (A. N. Krylova).

BARIUM COMPOUNDS

Soluble barium compounds that enter the body through the alimentary canal are absorbed in the stomach and cause poisoning.

Barium compounds are excreted from the body mainly through the intestines. Traces of these compounds are excreted through the kidneys and partially deposited in the bones. Information about the content of barium as a normal component of the cells and tissues of the body is not available in the literature.

MANGANESE COMPOUNDS

Manganese compounds are among the strongest protoplasmic poisons. They act on the central nervous system, causing organic changes in it, affecting the kidneys, lungs, circulatory organs, etc. When using concentrated solutions of potassium permanganate for gargling, swelling of the mucous membranes of the mouth and pharynx may occur.

Manganese compounds accumulate in the liver. They are excreted from the body through the alimentary canal and in the urine. During the pathological and anatomical autopsy of the corpses of persons who died as a result of poisoning with manganese compounds, burns of the mucous membranes in various parts of the alimentary canal are noted, resembling burns caused by caustic alkalis. Degenerative changes are found in some parenchymal organs.

CHROMIUM COMPOUNDS

In acute poisoning with chromium compounds, they accumulate in the liver, kidneys and endocrine glands. Chromium compounds are excreted from the body mainly through the kidneys. In this regard, when poisoning with these compounds, the kidneys and mucous membranes of the urinary tract are affected.

SILVER COMPOUNDS

Silver compounds that enter the stomach are absorbed into the blood in small quantities. Some of these compounds interact with the hydrochloric acid of the contents of the stomach and turn into chloride, which is insoluble in water. Silver nitrate acts on the skin and mucous membranes. As a result, "chemical" burns can occur. Upon entry into the body through Airways dust containing silver or its compounds, there is a danger of damage to the capillaries. Long-term intake of silver compounds inside can cause argyria (deposits of silver in the tissues), in which the skin becomes gray-green or brownish in color.

Silver compounds are excreted from the body mainly through the intestines.

COPPER COMPOUNDS

The absorption of copper compounds from the stomach into the blood is slow. Since copper salts that enter the stomach cause vomiting, they can be excreted from the stomach with vomit. Therefore, only small amounts of copper enter the blood from the stomach. When copper compounds enter the stomach, its functions may be disturbed and diarrhea may appear. After the absorption of copper compounds into the blood, they act on the capillaries, cause hemolysis, damage to the liver and kidneys. With the introduction of concentrated solutions of copper salts into the eyes in the form of drops, conjunctivitis may develop and damage to the cornea may occur.

Copper ions are excreted from the body mainly through the intestines and kidneys.

ANTIMONY COMPOUNDS

The antimony compounds that enter the blood act as a "capillary poison". In case of poisoning organic compounds Antimony disrupts the functions of the heart muscle and liver.

In the pathoanatomical examination of the corpses of persons poisoned with antimony compounds, there is hyperemia of the lung tissue, hemorrhage in the lungs and in the alimentary canal.

Antimony is excreted from the body mainly through the kidneys. Therefore, with antimony poisoning, nephritis can develop.

ARSENIC COMPOUNDS

Arsenic can accumulate in the body. In acute poisoning with arsenic compounds, they accumulate mainly in parenchymal organs, and in chronic poisoning - in bones and keratinized tissues (skin, nails, hair, etc.).

Arsenic is excreted from the body through the kidneys with urine, intestines and through some glands. The release of arsenic from the body is slow, which is the reason for the possibility of its accumulation. In excrement, arsenic can still be detected a few weeks later, and in cadaveric material - even a few years after death.

BISMUTH COMPOUNDS

Bismuth ions, absorbed into the blood, are retained in the body for a long time (in the liver, kidneys, spleen, lungs and brain tissue).

Bismuth is excreted from the body through the kidneys, intestines, sweat glands, etc. As a result of the accumulation of bismuth in the kidneys, they may be damaged. When bismuth is excreted from the body by the sweat glands, itching of the skin and the appearance of dermatoses can occur.

Data on the presence of bismuth as a normal component of the cells and tissues of the body are not given in the literature.

CADMIUM COMPOUNDS

Absorption of cadmium compounds occurs through the alimentary canal, and vapors through the respiratory tract. Soluble cadmium compounds denature the proteins contained in the walls of the alimentary canal. The cadmium ions that enter the blood combine with the sulfhydryl groups of enzymes, disrupting their functions. Cadmium compounds accumulate mainly in the liver and kidneys. They can cause fatty degeneration of the liver. Cadmium compounds are excreted from the body mainly through the kidneys with urine and intestinal walls. In a number of cases, in case of poisoning with cadmium compounds, intestinal bleeding is noted.

ZINC COMPOUNDS

Zinc and its compounds can enter the body through the food canal, as well as through the respiratory system in the form of dust generated during the extraction and processing of zinc ores. Zinc can enter the body with inhaled air in the form of vapors released during zinc smelting and alloy production. After zinc enters the body in the form of dust and vapors, its compounds with proteins are formed, causing bouts of fever, starting with chills (the so-called caster's fever, or brass fever). Inhalation of dust and zinc fumes may cause nausea, vomiting and muscle pain. Cases of poisoning by food prepared and stored in galvanized utensils, from products containing acids (fruits rich in acids, tomato, etc.) are described. Zinc compounds that enter the stomach can cause acute poisoning, in which vomiting, diarrhea, convulsions, etc. occur.

In case of poisoning with zinc compounds, they accumulate in the liver and pancreas.

MERCURY COMPOUNDS

Vapors of metallic mercury and dust containing compounds of this metal can enter the body with inhaled air. This affects the central nervous system (primarily the cerebral cortex). Entered into the body, metallic mercury and its compounds bind to sulfhydryl groups of enzymes and other vital proteins. As a result, the physiological functions of some cells and tissues of the body are disturbed. Mercury compounds that enter the body through the alimentary canal affect the stomach, liver, kidneys, and glands through which mercury is excreted from the body. At the same time, pain in the esophagus and stomach is felt, vomiting and bloody diarrhea appear. In the body, mercury is deposited mainly in the liver and kidneys.

Mercury is slowly excreted from the body. Even two weeks after acute mercury poisoning, certain amounts of it can be detected in individual tissues. Mercury is excreted from the body with urine and feces, as well as sweat, salivary and mammary glands.

Destruction of biological material. Mercury in biological material is in a bound form with sulfhydryl and some other functional groups of protein substances. In the process of destruction under the influence of strong acids, when heated, there is a rupture of strong covalent bonds between mercury and sulfhydryl or other functional groups of proteins. As a result of degradation, mercury passes into the destructate in the form of ions, which can be detected and determined using appropriate reactions and physicochemical methods. Thus, after the destruction of biological material, various amounts of mercury ions, proteins, peptides, amino acids, lipids, etc. are present in the destructate.

To accelerate the degradation, ethyl alcohol is added to the biological material, which is a catalyst for this process. Urea is added to remove nitric, nitrous acids and nitrogen oxides from the destructate, which are formed in the process of destruction.

Nitrogen oxides are oxidized by atmospheric oxygen to nitric oxide (IV), upon interaction of which with water, nitric and nitrous acids are formed, which are decomposed by urea, as indicated above.

The method of destruction of the organs of corpses. 20 g of crushed organs of corpses are introduced into a 200 ml conical flask, into which 5 ml of water, 1 ml of ethyl alcohol and 10 ml of concentrated nitric acid are added. Then 20 ml of concentrated sulfuric acid are added to the flask in small portions at such a rate that no nitrogen oxides are released from the flask. After the completion of the addition of concentrated sulfuric acid, the flask is left for 5-10 minutes at room temperature (until the release of nitrogen oxides stops). The flask is then placed in a boiling water bath and heated for 10-20 minutes. If, after heating the flask in a boiling water bath, pieces of biological material remain intact, then they are carefully rubbed with a glass rod on the walls of the flask. With the rapid course of the reaction with the release of nitrogen oxides, 30-50 ml are added to the flask hot water. The resulting hot destructate is mixed with a double volume of boiling water and, without cooling the liquid, it is filtered through a double humidified filter. The filter, through which the destructate was filtered, and the fat residues on it are washed 2-3 times with hot water. Wash water is added to the filtered destructate. The liquid thus obtained is collected in a flask containing 20 ml of a saturated solution of urea, intended for denitration of the destructate. Then the destructate is cooled, brought to a certain volume with water and examined for the presence of mercury.

Destruction of organic matter in the urine. In the urine of healthy people, mercury and its compounds are absent. However, in case of mercury poisoning, it can affect the kidneys and be excreted from the body in the urine in the form of compounds with proteins, amino acids and other organic substances. A certain amount of mercury can also pass into the urine in the form of ions. Therefore, to detect mercury in urine, it is necessary to destroy protein and other mercury-containing compounds that pass into the urine.

A. F. Rubtsov and A. N. Krylova developed two methods for the destruction of organic substances in urine:

1. A sample of unfiltered daily urine with a volume of 200 ml is introduced into a Kjeldal flask with a capacity of 500 ml. 35 ml of concentrated nitric acid, 2 ml of ethyl alcohol are added to the urine, and 25 ml of concentrated sulfuric acid are introduced into the flask in small portions. This acid is added so that the liquid in the flask does not foam and nitrogen oxides are not released from it. After the completion of the addition of concentrated sulfuric acid, the contents of the flask are heated on a boiling water bath for 40 minutes, then 20 ml of a saturated urea solution are added. If there is a precipitate in the destructate, then it is filtered off, the filter is washed with hot water. Wash water is added to the destructate, which is subjected to a study for the presence of mercury.

2. In a Kjeldal flask with a capacity of 500 ml, add 200 ml of unfiltered daily urine, to which 25 ml of concentrated sulfuric acid are added in small portions, and then 7 g of potassium permanganate are added in small portions. The contents of the flask are left for 40 minutes at room temperature, shaking occasionally, then a saturated solution of oxalic acid is added in small portions to the flask until the color of potassium permanganate disappears. The resulting destructate is used to detect and quantify mercury.

This method of destruction of protein substances in the urine is faster than that described above.

Destruction of organic substances in the blood. For this purpose, a technique is used that is used for the destruction of organs of corpses (see above), with the only difference that water is not added to the blood sample. 50-100 ml of blood is taken for the study.

METHYL ALCOHOL

Methyl alcohol (methanol) is a colorless liquid (bp 64.5 ° C, density 0.79), miscible in all proportions with water and many organic solvents.

Methyl alcohol can enter the body through the alimentary canal, as well as with inhaled air containing vapors of this alcohol. In small quantities, methyl alcohol can penetrate the body and through the skin. The lethal dose of methyl alcohol taken orally is 30-100 ml. Death occurs as a result of respiratory arrest, swelling of the brain and lungs, collapse or uremia. The local effect of methyl alcohol on the mucous membranes is stronger, and the narcotic effect is weaker than that of ethyl alcohol.

The simultaneous intake of methyl and ethyl alcohols in the body reduces the toxicity of methyl alcohol. This is due to the fact that ethyl alcohol reduces the rate of oxidation of methyl alcohol by almost 50%, and therefore reduces its toxicity.

Metabolism. Methyl alcohol that enters the body is distributed between organs and tissues. Nai large quantity it accumulates in the liver and then in the kidneys. Smaller amounts of this alcohol accumulate in muscle, fat, and the brain. The metabolite of methyl alcohol is formaldehyde, which is oxidized to formic acid. Some of this acid decomposes into carbon monoxide (IV) and water. Some unmetabolized methanol is excreted in exhaled air. It can be excreted in the urine as a glucuronide. However, small amounts of unchanged methyl alcohol may also be excreted in the urine. Methyl alcohol is oxidized in the body more slowly than ethyl alcohol.

ETHANOL

Ethyl alcohol C 2 H 5 OH (ethanol, ethyl alcohol, wine alcohol) is a colorless, volatile liquid with a characteristic odor, burning in taste (pl. 0.813-0.816, b.p. 77-77.5 ° C). Ethyl alcohol burns with a bluish flame, mixes in all proportions with water, diethyl ether and many other organic solvents, distills with water vapor.

Ethyl alcohol is unevenly distributed in tissues and body fluids. It depends on the amount of water in the organ or biological fluid. The quantitative content of ethyl alcohol is directly proportional to the amount of water and inversely proportional to the amount of adipose tissue in the body. The body contains about 65% of water from the total body weight. Of this amount, 75-85% of the water is contained in whole blood. Given the large volume of blood in the body, it accumulates a much larger amount of ethyl alcohol than in other organs and tissues. Therefore, the determination of ethyl alcohol in the blood is of great importance for assessing the amount of this alcohol that has entered the body.

Metabolism. Part of the ethyl alcohol (2-10%) is excreted unchanged from the body with urine, exhaled air, sweat, saliva, feces, etc. The rest of this alcohol is metabolized. Moreover, the metabolism of ethyl alcohol can occur in several ways. A certain amount of ethyl alcohol is oxidized to form water and carbon monoxide (IV). A slightly larger amount of this alcohol is oxidized to acetaldehyde and then to acetic acid.

ISOAMYL ALCOHOL

Isoamyl alcohol (CH 3) 2 -CH-CH 2 -CH 2 -OH (2-methyl-butanol-4 or isobutylcarbinol) is an optically inactive liquid (bp 132.1 ° C, pl. 0.814 at 20 ° C) with an unpleasant odor.

Isoamyl alcohol (2-methylbutanol-4) is the main constituent of fusel oils. The composition of fusel oils also includes optically active isoamyl alcohol CH 3 -CH 2 -CH (CH 3) -CH 2 -OH (2-methylbutanol-1), isobutyl alcohol and normal propyl alcohol. In addition to these alcohols, fusel oils contain small amounts of fatty acids, their esters and furfural. The presence of 2-methylbutanol-4 in fusel oils explains its sharp unpleasant odor and high toxicity. Isoamyl alcohol (2-methylbutanol-4) is a by-product of the alcoholic fermentation of carbohydrates found in beets, potatoes, fruits, grains of wheat, rye, barley and other agricultural crops.

Isoamyl alcohol is 10-12 times more toxic than ethyl alcohol. It acts on the central nervous system, has narcotic properties.

Metabolism. Part of the dose of isoamyl alcohol that enters the body is converted into isovaleric acid aldehyde, and then into isovaleric acid. Some of the unchanged isoamyl alcohol and the above metabolites are excreted from the body in the urine and exhaled air.

ETHYLENE GLYCOL

Ethylene glycol (HO-CH 2 -CH 2 -OH) is one of the representatives of dihydric alcohols that have toxicological significance. It is a colorless oily liquid (bp 197 ° C) with a sweetish taste. Ethylene glycol is miscible with water in all proportions, poorly soluble in diethyl ether, well-soluble in ethyl alcohol. Ethylene glycol is steam distilled.

Metabolism. The metabolism of ethylene glycol is complex. The main metabolic pathway of this drug is that it is oxidized to glycolic acid aldehyde HO-CH 2 -CHO, which is further oxidized to glycolic acid HO-CH 2 -COOH, which decomposes into carbon monoxide (IV) and formic acid. Part of the ethylene glycol in the body is converted to oxalic acid, which can cause kidney damage due to the deposition of oxalates in the renal tubules. Carbon monoxide (IV), as a metabolite of ethylene glycol, is excreted from the body with exhaled air. The remaining metabolites and part of unchanged ethylene glycol are excreted from the body in the urine.

Isolation of ethylene glycol from biological material. The method for isolating ethylene glycol from objects of chemical-toxicological analysis was proposed by N. B. Lapkina and V. A. Nazarenko. This method is based on the use of benzene as a selective carrier of ethylene glycol from objects to distillate. Benzene, together with ethylene glycol vapor and a small amount of water vapor, is transferred to the distillate. The water that is distilled in this case contains practically all the ethylene glycol.

For research take the liver of a corpse, which after poisoning contains more ethylene glycol than in other organs. In acute poisoning with ethylene glycol, the stomach and contents are also examined. 5 g of crystalline oxalic acid are added to 10 g of the liver or stomach contents, the mixture is triturated until a thin slurry is obtained, transferred to a 100 ml round-bottomed flask and 50 ml of benzene are added. The flask is closed with a vertically placed refrigerator 3, equipped with a device 2 for trapping water. The flask is then placed in a water bath and heated. Benzene vapor and the water and ethylene glycol entrained by it condense in the refrigerator and enter a special device. Since benzene (density 0.879) is on top of the water in this device (nozzle), it flows into the flask. The water and the ethylene glycol in it remain in the nozzle. After the end of the distillation, the device is disassembled and the amount of liquid necessary for analysis is taken from the nozzle with a pipette.

detection of ethylene glycol.

Oxidation reaction of ethylene glycol with periodate and detection of formed formaldehyde. As a result of this reaction, formaldehyde is formed, which can be detected using fuchsine sulphurous acid:

Oxidation of ethylene glycol with nitric acid and detection of oxalic acid. With repeated evaporation of ethylene glycol with nitric acid, oxalic acid is formed, which, with calcium salts, forms calcium oxalate crystals having a characteristic shape. These crystals in some cases appear after 2-3 days.

Reaction with copper sulfate. From the addition of copper sulfate and alkali to ethylene glycol, a compound is formed that has a blue color:

CHLOROFORM

Chloroform (trichloromethane) CHCl 3 is a colorless transparent volatile liquid with a characteristic odor. Miscible with diethyl ether, ethyl alcohol and other organic solvents, slightly soluble in water (see Table 1). Under the influence of light, air, moisture and temperature, chloroform gradually decomposes. In this case, phosgene, formic and hydrochloric acids can be formed.

Metabolism. Chloroform entering the body quickly disappears from the blood. After 15-20 minutes, 30-50% of chloroform is released unchanged with exhaled air. Within an hour, up to 90% of the chloroform that enters the body is excreted through the lungs. However, even after 8 hours, small amounts of chloroform can be detected in the blood. Part of the chloroform undergoes biotransformation. In this case, carbon monoxide (IV) and hydrogen chloride are formed as metabolites. In chemical-toxicological studies, the main objects of analysis for the presence of chloroform in the body are exhaled air, fat-rich tissues of corpses, and the liver.

Chloroform detection

Chlorine elimination reaction. When chloroform is heated with an alcoholic solution of alkali, chlorine atoms are split off, which can be detected by reaction with silver nitrate:

Before performing this reaction, it is necessary to make sure that there are no chloride ions in the test solution (distillate) and reagents.

Fujiwara reaction. Chloroform and a number of other halogen-containing compounds can be detected using the Fujiwara reaction, which is based on the interaction of these substances with pyridine in the presence of alkali. When chloroform reacts with pyridine and alkali, a polymethine dye is formed. In this reaction, a pyridinium salt is first formed:

Under the influence of alkali, the pyridinium salt is converted into a derivative of glutaconic aldehyde (I), upon hydrolysis of which glutaconic aldehyde (II) is formed, which has a color:

Two versions of the Fujiwara reaction have been described. When using the first option, the color of the resulting glutaconic aldehyde is observed. In the second variant of this reaction, an aromatic amine or another compound containing a mobile hydrogen atom is added to the resulting glutaconic aldehyde, and then the color is observed.

Reaction with resorcinol. When chloroform is heated with resorcinol in the presence of alkali, a pink or crimson-red color appears.

Isonitrile formation reaction. When chloroform is heated with primary amines and alkali, isonitrile (carbylamine) is formed, which has an unpleasant odor:

Reaction with Fehling's reagent. When chloroform interacts with alkali, a salt of formic (formate) acid is formed:

Fehling's reagent, containing the intracomplex compound K 2 Na 2 , which is formed by the interaction of copper (II) ions with Rochelle salt, oxidizes formic acid and its salts when heated. As a result of the reaction, a red precipitate of copper oxide (I) precipitates:

CHLOROALHYDRATE

Chloral hydrate or

Colorless crystals or finely crystalline powder with a characteristic pungent odor and slightly bitter, soluble in water, ethyl alcohol, diethyl ether and chloroform. Chloral hydrate is hygroscopic and volatilizes slowly in air.

Metabolism. Chloral hydrate is rapidly absorbed into the blood from the alimentary canal. It is metabolized in the body. The metabolites of chloral hydrate are trichloroethanol and trichloroacetic acid. It is believed that the toxic effect of chloral hydrate on the body is due to the formation of trichloroethanol. Trichloroacetic acid can be formed in the body in two ways: directly from chloral hydrate and from trichloroethanol. Trichloroethanol is excreted from the body in the urine as a glucuronide. After death resulting from poisoning with chloral hydrate, a certain amount of it in unchanged form can be found in the liver and stomach.

Detection of chloral hydrate

Chloral hydrate gives all the reactions that are used in chemical-toxicological analysis to detect chloroform. This is due to the fact that the reactions to chloroform used in the chemical-toxicological analysis are carried out in the presence of alkali, under the influence of which chloral hydrate decomposes with the release of chloroform:

To distinguish chloral hydrate from chloroform, a reaction with Nessler's reagent can be used. This reaction gives chloral hydrate containing an aldehyde group. Chloroform does not give this reaction.

Reaction with Nessler's reagent. When chloral hydrate interacts with Nessler's reagent, free mercury is released:

CARBON TETROCHLORIDE

Carbon tetrachloride CCl 4 is a clear liquid with a peculiar odor (bp 75-77 °C). It is miscible in any ratio with acetone, benzene, gasoline, carbon disulfide and other organic solvents. About 0.01% carbon tetrachloride dissolves in water at 20 °C. Carbon tetrachloride is not flammable, its vapors are several times heavier than air.

Carbon tetrachloride enters the body by inhalation of its vapors, and can also enter through intact skin and the alimentary canal. Carbon tetrachloride is unevenly distributed in the body. The amount of it in tissue rich in fats is several times greater than in the blood. The content of carbon tetrachloride in the liver and bone marrow is much higher than in the lungs. The blood erythrocytes of corpses contain approximately 2.5 times more carbon tetrachloride than plasma.

Metabolism. Carbon tetrachloride is rapidly excreted from the body. Already 48 hours after entering the body, it cannot be detected in the exhaled air. Its metabolites are chloroform and carbon monoxide (IV).

DICHLOROETHANE

Two isomers of dichloroethane (C 2 H 4 Cl 2) are known: 1,1-dichloroethane and 1,2-dichloroethane.

1,1-Dichloroethane (ethylidene chloride) CH 3 CHCl 2 is a colorless liquid (density 1.189 at 10 °C), boiling at 58 °C. 1,2-Dichloroethane (ethylene chloride) Cl-CH 2 -CH 2 -Cl - liquid (density 1.252 at 20 ° C), boiling at 83.7 ° C. In industry, 1,2-dichloroethane is more widely used than 1,1-dichloroethane.

1,2-Dichloroethane is slightly soluble in water, soluble in most organic solvents. It is resistant to acids and alkalis. It ignites with difficulty. Technical 1,2-dichloroethane contains an admixture of trichlorethylene C1-CH = CC1 2 .

Isolation of dichloroethane from biological material. Separation of dichloroethane from biological material is carried out by steam distillation. The first portions of the distillate are taken for research. In cases where there are special instructions to examine the biological material for the presence of 1,2-dichloroethane, about 300 ml of distillate is obtained, which is subjected to repeated distillation and the first 200 ml of distillate are collected. This distillate is refluxed twice. The last distillate (volume 10 ml), obtained by distilling off the liquid with a reflux condenser, is subjected to a study for the presence of 1,2-dichloroethane.

FORMALDEHYDE

Formaldehyde (aldehyde formic acid) is a gas that is highly soluble in water and has a sharp specific odor. An aqueous solution containing 36.5-37.5% formaldehyde is called formalin.

Formaldehyde is isolated from biological material by steam distillation. However, only a small part of the formaldehyde is distilled by this method. It is believed that formaldehyde is aqueous solutions is in the form of a hydrate (methylene glycol), which is difficult to distill with steam:

HCHO + HOH ---> CH 2 (OH) 2.

Formaldehyde depresses the central nervous system, as a result of this, loss of consciousness may occur, convulsions appear. Under the influence of formaldehyde, degenerative lesions of the liver, kidneys, heart and brain develop. Formaldehyde affects some enzymes. 60-90 ml of formalin is a lethal dose.

Metabolism. Formaldehyde metabolites are methyl alcohol and formic acid, which, in turn, undergo further metabolism.

Formaldehyde detection

Reaction with chromotropic acid. Chromotropic acid (1,8-dioxinaphthalene-3,6-disulfonic acid) with formaldehyde in the presence of sulfuric acid gives a violet color.

Determination of organic substances in water. Determination of lead in urban vegetation Qualitative analysis of lead content in biological material

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