RU2236916C1 - Method of determining weight concentration of benzo-a-pyrene in soil - Google Patents

Abstract

FIELD: analytical methods agriculture.

SUBSTANCE: method comprises extracting benzo-a-pyrene from soil sample with hexane, removing impurities from extract and concentrating the latter, measuring concentration of benzo-a-pyrene in resulting concentrate by fluorescence produced from exciting light, and correcting thus obtained concentration using correction coefficients. Extraction is performed by holding a weighed amount of benzo-a-pyrene in a vessel with hexane at normalized surrounding atmosphere temperature (20±10^оС) and benzo-a-pyrene concentration measurement is performed by fluorescence-assisted identification of chromatographic peaks of benzo-a-pyrene involving juxtaposition of chromatograms of benzo-a-pyrene extract concentrate and reference hexane solutions of benzo-a-pyrene, the two being irradiated by exciting light at normalized surrounding atmosphere temperature (20±10^оС).

EFFECT: simplified analytical procedure, accelerated analysis, and increased analytical accuracy.

9 cl, 1 tbl

Description

The invention relates to the field of determining mass concentrations of toxic substances, for example, in soil, industrial waste, etc., and can be used by organizations and institutions that monitor the toxicity of the biocenosis environment, nature protection, integrated monitoring of the earth's surface, laboratory studies of environmental pollution environment, etc.

Toxic substances, including polycyclic aromatic hydrocarbons (for example, benz-a-pyrene), are widespread in almost the entire human environment. Benz-a-pyrene (BP) is one of the most common toxicants (chemical carcinogens) and is present in atmospheric air, in soil, in water.

BP is a crystalline substance, practically insoluble in water (0.012 mg / l), quite soluble in organic solvents (hexane, benzene, ether, ethanol, oils, etc.). The maximum permissible concentration (MPC) of benz-a-pyrene in the soil is 0.02 mg / kg.

The main sources of BP are industrial enterprises, thermal power plants, heating systems, and motor vehicles. BP is formed during the combustion of materials, therefore it is present in smoke, soot, soot (in the resinous substances contained in the combustion products).

The combustion process (carbon oxidation) is not necessary for the occurrence of BP, because BP is formed during the polymerization of simple radicals obtained from the original fuel from high temperatures. The formation of the bulk of BP and other polycyclic aromatic hydrocarbons occurs at a temperature of 500-800 ° C. In addition to the high-temperature (free-radical) process for the formation of polycyclic aromatic hydrocarbons, there is a low-temperature process that occurs in the range of 250-400 ° C (for example, during wood pyrolysis), in which BP formation occurs as a result of ionic reactions.

BP enters the soil from atmospheric precipitation and from dying plants, as well as from some components used as fertilizers.

A known method (technique) for determining the mass concentration of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere, based on the capture of solid dust particles from the air by a filter or sorbent, on the extraction of PAHs from dust particles by n-hexane, on the separation of PAHs using preparative thin layer chromatography (TLC) from interfering impurities in determining the mass concentration of PAHs using liquid chromatography (“Guidelines for the Control of Atmospheric Pollution”, RD 52.04. 186-89, Hydrometeoizdat, pp. 647-657).

A known method (technique) for determining the mass concentration of BP in drinking water, based on the extraction of BP from water samples with n-hexane, on the separation of BP using preparative thin layer chromatography (TCS) from impurities, on the determination of the mass concentration of BP using liquid chromatography (GOST R 51310-99, State Standard of the Russian Federation, drinking water).

Known methods are not intended and cannot be used to determine the mass concentration of BP in the soil, since the technology for sampling and preparing samples for laboratory research from gas and liquid (from air and water) differs from the technology for sampling and preparing samples for laboratory research from solid matter (from soil).

In addition, the known methods do not provide high-quality separation of unsubstituted and alkyl-substituted PAHs; therefore, the results obtained using them can be considered only as the mass concentration of the sum of all pyrene derivatives (PAHs), and not separately BP, as is done in the proposed method.

A known method for determining the mass concentration of BP in air, water, soil samples, based on extracting BP from air, water, soil samples with an organic solvent (n-hexane), freezing the BP extract with liquid nitrogen (-198 ° C), irradiating the frozen BP extract with a stream UV radiation with a wavelength of not more than 365 nm, analysis of the BP fluorescence spectrum at the length of the analytical quasiline of 402.4 nm, the intensity of which is proportional to the content of BP in the solution (Guidelines. Determination of the mass fraction and mass concentration of BP in samples ozduha, soil, water and sediment method of measurement method of quasi-line fluorescence spectra RD 52.18, SPA "Typhoon", 2000 -.. a prototype).

The disadvantages of this method are the complexity of the technology and equipment for work (mandatory freezing of the extract concentrate BP liquid nitrogen), as well as a large error in determining the mass concentration of BP in the sample of the test substance (for example, in the soil). This error occurs because

- determination of the mass concentration of BP in the obtained concentrate of the extract of BP is made by comparing the intensity of the analytical line of BP (the spectrum of its fluorescence from the action of UV radiation) in the studied concentrate of the extract of BP and in standard solutions of BP, which gives a big error (the approximate mass concentration of BP is determined in a practically known way in the sample);

- a different amount of BP present in different samples of the test substance is extracted with the same amount of solvent (n-hexane), in this connection, in each case, a BP extract of different saturation is obtained, which leads to different conditions for the final extraction of BP (the more BP the extraction solvent is saturated, the worse, it extracts BP remaining in the soil sample, and the greater part of BP remains in the sample not extracted and is not taken into account);

- on the walls of the container in which the BP is extracted, and on the surface of the particles of the test sample, there remains a part of the un drained BP extract, which is lost and the BP contained in it is not taken into account.

The aim of the proposed method is to eliminate the above disadvantages, that is, simplification of technology and equipment, improving the accuracy of determining the mass concentration of BP in the test sample due to

- extraction of almost the entire BP from a sample of the test sample with a specific amount of an organic solvent (hexane);

- collection of almost the entire BP extract from the extraction vessel and from the test sample by washing it with hexane and mixing the wash with the BP extract;

- exceptions from the technology for determining the mass concentration of BP in the test sample of freezing the concentrate of the extract of BP with liquid nitrogen;

- reducing time and improving the extraction of BP by moving the container with a sample of the test sample filled with hexane in the vertical and / or horizontal plane (intensive mixing of hexane and a sample of the test sample);

- improving the accuracy of determining the mass concentration of BP in the test sample by recording on a chromatograph and identifying chromatographic peaks of BP fluorescence in a concentrate of BP extract and in BP reference solutions;

- refinement of the mass concentration of BP in the sample obtained by identifying the chromatographic peaks of BP in the extract and standard solutions, using a special formula that takes into account the conditions for the extraction of BP.

This goal is achieved by the fact that in the proposed method, including the extraction of BP from a sample of the test soil with an organic solvent (for example, hexane), purification of the obtained BP extract from impurities and its concentration, determination of the mass concentration of BP in the obtained extract concentrate by its fluorescence during action exciting light, the calculated refinement of the obtained mass concentration of BP by correction factors, the extraction of BP from a sample of soil sample is carried out by exposure of the sample and soil samples for a period of at least 20 hours in a container with hexane at ambient temperature reduced to normal conditions, i.e. at 20 ± 10 ° С, and the mass concentration of BP in the purified concentrate of its extract is determined by identifying chromatographic peaks of BP fluorescence, recorded on the chromatograms of the concentrate of the extract of BP and the standard solutions of BP in hexane during the action of exciting light on them at ambient temperature reduced to normal conditions, for example, at 20 ± 1 0 ° C.

The mass concentration of BP in a soil sample, determined by the identification of chromatographic peaks of BP fluorescence on the chromatograms of a BP extract from a sample of a soil sample and BP reference solutions during the action of exciting light on them, is calculated (specified) by the formula:

where C is the calculated (specified) mass concentration of BP in the soil sample, μg / cm ³ ;

C _{o is the} mass concentration of BP in the extract, determined by the identification of the chromatographic peaks of BP fluorescence on the chromatograms of the BP extract and BP reference solutions in hexane during the action of exciting light on them, μg / cm ³ ;

With _n - mass concentration of BP in a saturated hexane solution, µg / cm ³ ;

N _o - the ratio of the volumetric amount of hexane in the extract to the mass amount of extracted BP;

N _n - the ratio of the volumetric amount of hexane in a saturated solution to the mass amount of BP dissolved in it.

To reduce the error in determining the mass concentration of BP in a soil sample (to increase the amount of BP extracted from a sample of a soil sample), BP is extracted with hexane in relation to the amount of BP in the sample, greater than its ratio to the amount of BP in a saturated solution of BP in hexane, for example not less than five times.

To improve the extraction of BP from a sample of soil samples and to reduce the time of extraction, a container with a mixture of soil and hexane is exposed to sound (vibrations of atmospheric air) with a power of at least 50 dB, for which a sound source, for example a speaker emitting a sound, is placed next to the container, and sound extraction produce over a period of not less than 0.5 hours.

To improve the extraction of BP from a sample of the soil sample and to reduce the time of extraction, the container with a mixture of soil and hexane is moved in a vertical and / or horizontal plane with a frequency of 0.1-10.0 Hz and with an amplitude of 0.5-5.0 mm, why the container is installed on a vibrating table, and vibration extraction is carried out for at least an hour.

To reduce the error in determining the mass concentration of BP in the soil sample, the container in which the BP is extracted and the sample of soil from which the BP is extracted, after draining the obtained BP extract from them, is washed at least three times with a volume of hexane no less than three times the volume of the sample, which is added to the merged extract BP.

To reduce the error in determining the mass concentration of BP in the soil when detecting the mass concentration of BP in a soil sample close to the MPC, a second laboratory study of a new sample of this sample is carried out using an increased amount of extracting hexane, for example, an amount of hexane no less than twice that the number in a laboratory study of the first sample, or using a reduced amount of the studied soil, for example, with the study of a new sample of the same soil sample, weight or volume Torah not less than twice the smaller mass or volume of the first sample.

To simplify the technology of work when determining the mass concentration of BP in a large number of soil samples with background, that is, with little pollution, BPs are extracted from a sample of soil with a volume of hexane no less than three times the volume of the studied sample of soil sample.

To reduce the error in determining the mass concentration of BP in the soil, the mass concentration of BP in the soil sample is determined as the arithmetic mean of the results of two autonomous laboratory studies of two autonomous samples from this sample, carried out under the same conditions (taking into account current standards for monitoring the accuracy of measurements and reproducibility) and calculated according to one formula.

The set of essential features of the proposed method exhibits new properties, namely, that the accuracy of determining (control) the mass concentration of BP in the soil sample is increased, the technology and equipment of laboratory work are simplified.

Thus, the proposed solution meets the criteria of “novelty” and “inventive step”.

The determination of the mass concentration of BP in the soil by the proposed method is as follows.

In accordance with GOST 17.4.3.01-83, GOST 17.4.4.02-84, a test soil is taken and prepared for research. For this, a soil sample is thoroughly mixed, freed from stones and roots, quartered. In the laboratory, the soil sample is brought to an air-dry state, ground in a porcelain mortar, sieved through a sieve with a mesh, for example, 1 mm, and weighed samples from it (for example, 10.0 g each). The remainder of the soil sample is stored in a sealed container, at a temperature not exceeding 8 ° C, for a period of not more than a month, in a dark place.

One prepared sample of an air-dry soil sample is placed in a glass flask (container) with a ground stopper, poured into a hexane flask and kept for at least 20 hours at ambient temperature brought to normal conditions, i.e. at 20 ± 10 ° С .

The amount of hexane poured into the tank in relation to the amount of BP in the soil sample should be no less than five times this ratio in a solution of BP in hexane saturated to an equilibrium concentration to provide a reduced error in the determination of BP in the soil sample. The approximate amount of BP in the soil sample is taken from the data available in the documentation or equated to the amount available in neighboring areas.

The technical essence of the above condition on the relative amount of hexane is explained by the fact that the extraction of hexane by the BP present in the sample of soil will be more efficient and complete as the BP will be less contained in the extracting hexane.

It should be especially noted that the fulfillment of the proposed condition for extracting BP from various soil samples containing different amounts of BP provides the same error in the final result — determination of the mass concentration of BP in all studied soil samples, which is important not only for determining the actual mass concentration of BP in soils and its comparison with MPC, but also for a comparative assessment of the mass concentration of BP of soils in other areas.

If in any soil sample the above technology determines a sufficiently large mass concentration of BP, for example, close to the MPC (that is, the above conditions for the quantitative ratio of BP and hexane are not met due to an incorrectly accepted value of the expected amount of BP in the soil), then for this a specific soil sample, an additional laboratory study of the second sample is carried out using an increased amount of hexane (for example, the amount of hexane, not less than twice Witzlaus its amount at a laboratory study of the first sample) or with a reduced amount of the investigated soil hitch (for example, lifting the soil sample, the mass or volume which is not less than half the weight or volume of the first sample).

To exclude such possible repeated laboratory studies of soil samples, it is possible to take a known large identical amount of hexane to extract BP from all the first samples of soil samples with different amounts of mass concentration of BP (for example, several tens of times more than the above ratio). This will reduce the error in determining the mass concentration of BP to an acceptable level in a wide range of variation in the content of BP in soil samples, but will complicate the preparation of a concentrate of BP extract (to increase the time of evaporation of a large amount of hexane from BP extracts).

When determining the mass concentration of BP in a large number of soil samples with background, that is, slight pollution, it is advisable to extract BP from a sample of soil sample with a hexane volume not less than three times the volume of the sample sample to be examined, which ensures the required completeness of extracting PS from a sample of soil and the required error.

The resulting mixture of hexane with a weighed sample from a soil sample is kept in a flask at an ambient temperature reduced to normal conditions (+ 20 ± 10 ° С) for a period of at least 20 hours, during which almost all BP available in the soil is extracted from a sample in hexane.

To improve the extraction of BP from a sample of soil samples and to reduce the time of extraction of BP, a container with a mixture of soil with hexane is exposed to sound (vibrations of atmospheric air) with a power of at least 50 dB. To do this, a sound source, for example a speaker emitting a sound, is placed next to the container, and sound extraction is performed for at least 0.5 hours.

To improve the extraction of BP from a sample of soil samples and to reduce the time of extraction of BP, a container with a mixture of soil and hexane is moved in a vertical and / or horizontal plane with a frequency of 0.1-10.0 Hz and with an amplitude of 0.5-5.0 mm . To do this, the container is installed on a vibration table, and vibration extraction is carried out for at least an hour.

Perhaps a combination of sound and vibration extraction PSU.

After extraction, the resulting BP extract is poured (pipetted) from the container into the bottle. To reduce the error in determining the mass concentration of BP in the soil sample, the capacity in which the BP was extracted and the sample of the soil from which the BP was extracted, after draining the BP extract obtained from them, is washed with hexane at least three times, the volume of which is no less than three times the volume of the studied sample of soil samples. Washing hexane is added to the BP fusion extract.

When BP is extracted into hexane from a sample of the soil sample, in addition to BP, substances of a different nature pass (are extracted), which interfere with the determination of the mass concentration of BP in the extract. To eliminate this effect, the extract is purified from impurities by chromatography in a thin layer of alumina.

To do this, concentrate the extract (evaporate in the bottle by natural means with a fan to dryness), after evaporation, add 1.0 cm ^{3 of} hexane to the bottle and apply 0.5 cm ^{3 of the} resulting mixture and 0.5 cm ^{3 of} each BP standard solution on a chromatographic plate using a micropipette . Chromatographic separation of substances (purification of the extract) is carried out in the medium: petroleum ether - diethyl ether (40: 1). Under UV irradiation, three zones with different fluorescence colors (counting from the start line) appear on the chromatographic plate: light green (1st zone); purple (2nd zone); blue (3rd zone).

The violet glow of the 2nd zone indicates the presence of BP in the mixture. Using a spatula from this zone, the mixture of alumina with BP is transferred to the box and BP is extracted from it with hexane. The extraction is carried out with hexane, three times in 3 ml portions (in total 9 ml of hexane are poured into the bottle, three times with a 3 ml pipette). The obtained BP extract is filtered through a “blue ribbon” paper filter into a bottle, evaporated naturally to “wet salts”, 0.5 cm ^{3 of} hexane is added to it and the obtained BP extract concentrate is transferred to tubes with ground stoppers and chromatographed, that is determination of mass concentration of BP in the studied soil sample (in a purified concentrate of BP extract).

The chromatographic conditions of the obtained purified BP extract concentrate are selected depending on the type of liquid chromatograph and chromatographic column used. As an example, the following chromatographic conditions for determining the mass concentration of BP in a purified concentrate of its extract can be given:

- liquid chromatograph "Milichrom" with a fluorescent detector;

- column “Diasorb-BP”, with a grain size of 6 microns, a length of 80 mm, ⌀2 mm;

- fluorimetric detector with a wavelength of exciting light 295 nm, an emission filter 418-430 nm;

- mobile phase - acetonitrile and water in a volume ratio of 8: 2;

- the rate of elution (concentration) of 100 μm / min,

- the volume of the injected sample 10 μl.

The gain sensitivity is selected so that the intensity of the PSU signal does not exceed 95% of the scale.

When exposed to the studied purified concentrate of BP extract from a sample of soil samples and to reference solutions of BP of exciting light, peaks of BP fluorescence are recorded on a chromatograph.

The chromatographic peaks of BP fluorescence in the chromatograms are identified using the “additive method”. To do this, the studied BP extract concentrate and the BP reference solution are mixed in a microsyringe, irradiated with exciting light, and the chromatograms of BP solutions from exciting light are recorded at least twice (to exclude possible distortions and recording failures). Comparing then the recorded chromatograms find the peaks related to the determined BP.

The volume and concentration of BP reference solutions are chosen such that the peak of BP is clearly visible on the chromatograms (it is 1.5-2.0 times larger than other peaks), but so that it does not mask nearby peaks.

To increase the accuracy of determining the mass concentration of BP in a soil sample, BP is simultaneously extracted separately from two identical weights of one soil sample, the extract of BP for each sample is separately purified from the impurities by the same technology, and the mass concentration of BP in each sample is determined by chromatography soil, if necessary, separately specify it by calculation according to a special formula.

If there is a large variation in the mass concentration of BP in these two samples (for example, more than 10%), find out the causes of this large variation, eliminate them and conduct an additional laboratory study of the third sample from this soil sample or repeat laboratory tests on two new samples from this soil sample .

To simplify the technology of work when determining the mass concentration of BP in a large number of soil samples with background, that is, with little pollution, BPs are extracted from all samples of soil samples with a hexane volume not less than three times the volume of each sample of the soil sample.

To reduce the error, the mass concentration of BP in each studied soil sample is determined as the arithmetic mean of the slightly differing (less than 10%) results of the two above-mentioned stand-alone laboratory tests of two stand-alone hangings from this sample, carried out under the same conditions (taking into account the current standards for monitoring measurement accuracy and reproducibility) and calculated according to one formula.

The mass concentration of BP in the soil sample, determined by the identification of chromatographic peaks of BP fluorescence on the chromatograms of the concentrate of the BP extract in each of two samples of the soil sample and BP standard solutions during the action of exciting light on them, is calculated (specified) by the prototype formula, or by the following formula:

where C is the calculated (specified) mass concentration of BP in the soil sample, μg / cm ³ ;

With _{about the} mass concentration of BP in the concentrate of the extract, determined by the identification of chromatographic peaks of fluorescence of BP in the chromatograms of the concentrate of the extract of BP and the standard solutions of BP in hexane during exposure to exciting light, μg / cm ³ ;

With _n - mass concentration of BP in a saturated hexane solution, µg / cm ³ ;

N _o - the ratio of the volumetric amount of hexane in the extract to the mass amount of extracted BP;

N _n - the ratio of the volumetric amount of hexane in a saturated solution to the mass amount of BP dissolved in it.

The table shows the experimental data on the mass concentration of BP in 60 soil samples determined by the proposed method in the laboratory of the Federal State Institution “Center for Sanitary Inspection in the Voronezh Region”.

Due to the fact that the known method (prototype) is laborious, requires special equipment and additional working fluid (liquid nitrogen), a comparative determination of the mass concentration of BP in these soil samples by the known method was not carried out.

The proposed method can be used when performing work on the land cadastre, monitoring of land and objects, monitoring and managing land resources and property, land management, when determining the mass concentration of BP and other toxicants in the soil and in other substances.

Claims (9)

1. The method of determining the mass concentration of benz-a-pyrene in the soil, including extraction of benz-a-pyrene from a soil sample with hexane, purification of the obtained extract from impurities and its concentration, determination of the mass concentration of benz-a-pyrene in the obtained extract concentrate by its fluorescence from the action of exciting light on it, the calculation refinement of the obtained mass concentration of benz-a-pyrene by correcting coefficients, characterized in that the extraction of benz-a-pyrene from a sample of the soil is carried out by exposure weighed portions for a period of at least 20 hours in a container with hexane at ambient temperature reduced to normal conditions, i.e., at (+ 20 ± 10) ° С, and determination of the mass concentration of benz-a-pyrene in the purified concentrate of its extract is carried out by identification chromatographic peaks of benzo-a-pyrene fluorescence on chromatograms of a concentrate of benz-a-pyrene extract and standard solutions of benzo-a-pyrene in hexane during exposure to exciting light at ambient temperature brought to normal conditions, o is at (+ 20 ± 10) ° C. 2. The method according to claim 1, characterized in that the mass concentration of benz-a-pyrene in the soil sample, determined by the identification of chromatographic peaks of fluorescence of benz-a-pyrene on the chromatograms of the extract concentrate from the soil sample and standard solutions of benz-a-pyrene from the action on them exciting light, specify by the formula

where C is the calculated (specified) mass concentration of benz-a-pyrene in the soil sample, μg / cm ³ ; С _о - mass concentration of benz-a-pyrene in the extract concentrate, determined by the identification of chromatographic peaks of the fluorescence of benz-a-pyrene on the chromatograms of the concentrate of the extract of benz-a-pyrene and standard solutions of benz-a-pyrene in hexane during exposure to excitation light , mcg / cm ³ ; With _n - mass concentration of benz-a-pyrene in a saturated hexane solution, μg / cm ³ ; N _o is the ratio of the volumetric amount of hexane in the extract to the mass amount of extracted benz-a-pyrene; n _n is the ratio of the volumetric amount of hexane in a saturated solution to the mass amount of benz-a-pyrene dissolved in it. 3. The method according to claim 1, characterized in that the benz-a-pyrene is extracted from the sample of the soil with the amount of hexane, in relation to the amount of benz-a-pyrene in the sample, its ratio to the amount of benz-a-pyrene in a saturated solution benz-a-pyrene in hexane, for example, not less than 5 times. 4. The method according to claim 1, characterized in that when extracting benz-a-pyrene with hexane from a weighed sample of the soil, the container with a mixture of soil with hexane is affected by sound, that is, atmospheric air vibrations with a power of at least 50 dB, for which a sound source is placed with the container, for example, a speaker that emits sound, and sound extraction is performed for at least 0.5 hours. 5. The method according to claim 1, characterized in that during the extraction of benz-a-pyrene with hexane from a sample of soil sample, the container with a mixture of soil and hexane is moved in a vertical and / or horizontal plane with a frequency of 0.1-10.0 Hz and with an amplitude of 0.5-5.0 mm, for which the capacity is installed on a vibration table and vibration extraction is carried out for at least an hour. 6. The method according to claim 1, characterized in that the container in which the benz-a-pyrene is extracted, and the sample of soil from which the benz-a-pyrene is extracted, after draining the obtained benz-a-pyrene extract from them, is not less than washed three times with a volume of hexane not less than three times the volume of the sample, which is added to the benz-a-pyrene fusion extract. 7. The method according to claim 1, characterized in that when a mass concentration of benz-a-pyrene is detected in a soil sample close to the MPC, a laboratory test of the second sample from a sample of this soil is performed using an increased amount of extracting hexane, for example, the amount of hexane, not less than twice its amount in a laboratory study of the first sample, or using a reduced amount of test soil, for example, with a sample of soil sample, the mass or volume of which is not less than two times less than the mass or the first hitch. 8. The method according to claim 1, characterized in that when determining the mass concentration of BP in a large number of soil samples with background, that is, slight pollution, BP is extracted from a sample of soil with a volume of hexane not less than three times the volume of the sample sample the soil. 9. The method according to claim 1, characterized in that the mass concentration of benz-a-pyrene in the soil sample is determined as the arithmetic mean of the slightly different results of two autonomous laboratory studies of two autonomous samples of this sample, carried out under the same conditions, taking into account the current standards for measuring accuracy control and reproducibility and calculated according to one formula.