RU2358899C1 - Method for extraction of mercury and selenium inorganic forms from solid samples of natural objects - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for extraction of the mercury and selenium inorganic forms from the solid samples of natural objects includes mercury and selenium extraction from the solid phase of the natural objects to the organic phase of the settling system "water-antipyrin-sulfosalicylic acid". The latter was prepared by the mixing of antipyrin and sulfosalicylic acid 2M solutions in volume ratio 2:1.

EFFECT: decreasing of environment contamination during preparation of the solid samples of natural objects.

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Description

The invention relates to analytical chemistry, namely to the field of preparing solid samples of environmental objects for the extraction of mercury and selenium, in particular its inorganic forms from conservative objects of nature for quantitative determination by physicochemical methods.

A known method (analogue) of atomic absorption determination of mercury in the mineralized solid natural objects: vegetation, bottom sediments, soil. In the literature [Control of chemical and biological parameters of the environment. / Ed. L.K. Isaeva, Ecological and Analytical Center “Soyuz”, St. Petersburg, 1998, 896 pp., S.380-382, S.423-424. J.V. Loon. Selected methods of trace analysis: biological and environmental samples. 1985, NY, Chichester, Brisbane, Toronto, Singapore, - 357 p.] Presents a number of toxicant control methods in natural objects from 0.001 to 50 μg / g. The mercury content is characteristic of natural objects: soils, ores and plants. Clark concentration of mercury in sedimentary rocks is 0.4 μg Hg / g, and selenium 0.6 μg Se / g [Perelman A.I. Geochemistry. - M .: Higher. school., 1989. S. 287]. The average concentration of mercury in the air-dry plant mass of land is 0.012 μg / g, for selenium - 0.05 μg Se / r [Dobrovolsky V.V. Fundamentals of biogeochemistry. - M., 2003, - 400 p.]. These averages are used to evaluate the monitoring results of natural sites. In the case of taking samples of solid natural objects in the amount of 0.5-1.0 grams, preparation of the acid mineralizate of the natural object in a certain volume of 25-50 ml the hydride method of "cold steam" allows you to determine mercury and selenium in geological and biological objects using the calibration graph in optimal linearity of the used monitoring techniques.

The main disadvantage of the analogue is the mismatch of the analytical sample preparation method with the requirements of "green chemistry" and the inevitable loss of vapor of elemental mercury and its volatile compounds (Hg, Hg ₂ (NO ₃ ) ₂ , Hg (NO ₃ ) ₂ , Hg ₂ O, HgO, HgSO ₄ ) when heated without appropriate laboratory equipment (mineralizer, heat-resistant flask with reflux condenser). For selenium, the loss of volatile trace elements (Se ₂ Cl ₂ , SeO ₃ , SeOCl ₂ ) is inevitable when heated during ashing.

Of the known technical solutions, the closest (prototype) in purpose and technical essence to the claimed object is the method of "wet ashing" of a solid natural object in a mixture of mineral acids [R. Bock. Decomposition methods in analytical chemistry: translation from English. / Edited by A.I. Busev, M.V. Trofimova. - M., 1984, - 432 p.]. The method of “wet ashing” is based on the oxidation of elements to higher oxidation states by concentrated nitric acid when a sample of a solid natural object is heated in a water bath in a special mineralizer or heat-resistant flask with a reflux condenser to condense the reflux of gaseous decomposition products. In a mixture of acids, sulfuric acid is necessarily present, which destroys the organic forms of mercury and selenium. For the destruction and dissolution of the forms of elements in the process of "wet ashing", in addition to the listed acids, hydrochloric acid is introduced, which acts as a complexing agent on mercury and selenium, thereby binding it to chloride complex compounds, which are more resistant to heat than oxides and nitrates . The mineralizate of a solid natural object is prepared by the known method of “wet ashing” of a solid sample of a natural object (soil, ore, vegetation) in a mixture of mineral and maximally concentrated acids when heated in a water bath for one hour, followed by bringing the acid extract (KB) with distilled water to 25 , 50 ml in a volumetric flask at room temperature.

The disadvantages of the prototype include:

- mismatch of the method with the requirements of "green chemistry" due to the use of aggressive mineral acids (nitric, sulfuric, hydrochloric and others) and heating (water bath, electric stove); - the formation of toxic gaseous emissions of acidic nitrogen and sulfur oxides, the condensation of which requires special laboratory equipment: a mineralizer or a heat-resistant flask with a reflux condenser and an efficient exhaust system;

- special care is required when bringing the acid extract (KB) to a certain volume, first in a mineralizer (heat-resistant flask), then in a volumetric flask (25, 50 ml) at room temperature.

The disadvantages of the prototype completely eliminates the claimed method.

The method of extraction of inorganic forms of mercury and selenium from solid samples of natural objects does not require heating a sample of a natural object, ordinary glass bottles with ground covers are used to exclude sample losses when taking samples of solid natural material, usually prepared in the form of an air-dry mass of dispersed powder ( soil, ore, plants, fish, etc.).

In the proposed method, three components are used: water, antipyrine and sulfosalicylic acid. Moreover, the latter two are solids, which ensures the convenience and safety of the analyst.

As an active reagent for the extraction of inorganic mercury and selenium from solid objects of nature, a specially prepared dense ionic liquid in nature and organic in composition is used. The quantitative extraction characteristics of the prepared organic liquid are established on model solutions of mercury and selenium. Model solutions of mercury are prepared by sequential dilution of a concentrated 1 mg / ml standard solution of mercury (II) (GSO 7263-69). Ongoing testing of mercury and selenium in model solutions is carried out by the introduced-found hydride method. The extraction characteristics of the prepared organic phase are established on model solutions of selenium. A working solution of selenium 5 μg Se / ml was prepared from GSO 7779-2000 selenium (IV) with a concentration of 1 mg Se / ml by the method of sequential dilution. Calibration dependencies are obtained immediately before measurements. A single-beam atomic absorption spectrometer without background correction serves as a means of measuring the analytical signal. A solution for the background is selected with 0.1 M HCl. As a reducing agent, a 3% aqueous solution of sodium borohydride in 1% sodium hydroxide is used.

The essence of the proposed method of extraction (EC) is the extraction of mercury and selenium from the solid phase of a natural object into the organic component of the stratified system H ₂ O - AntH (antipyrine) - HSSA (sulfosalicylic acid). For the implementation of the invention using the following substances:

- antipyrine "pharmacopeia" (gross formula C ₁₁ H ₁₂ N ₂ O, melting point 113 ° C, molecular weight 188.23 g / mol),

- sulfosalicylic acid 2 - water (GOST 4478-78, gross formula C ₇ H ₆ O ₆ S × 2H ₂ O, molecular weight 254.21 g / mol).

The proposed method differs from the prototype in that the organic phase of the exfoliating system is used, consisting of three components: water, antipyrine and sulfosalicylic acid, and antipyrine is an antipyretic drug and is available for analysts.

The implementation of the invention is achieved as follows, for mercury: - immediately before measurements by successive dilution of GSO mercury (II) with a concentration of 1 mg / ml, a working solution with a concentration of 0.05 μg Hg / ml is prepared, then a series of standard solutions of mercury are prepared from the working solution with concentrations of 1.25-20.0 μg / l to build a calibration graph;

- 0.1 M hydrochloric acid is used as the background electrolyte in the hydride method of “cold steam” (the required amount of mercury is introduced into the reaction tube with a microdoser and the reaction volume is adjusted to 10 ml with a background HCl solution);

- when determining the degree of extraction into the organic phase by separation, the organic and aqueous phases are analyzed for mercury separately (the aqueous phase is taken in an aliquot of 5 ml, organic 0.5 ml, to reduce foaming, the organic phase is diluted with 2.5 ml of a background solution of 0.1 M HCl) ;

From a flask with a 3% alkaline solution of NaBH _4, 1.0 ml of a reducing agent with argon is fed into the reactor with an aliquot of an aqueous phase (WF), an organic phase (RP), and an extract. Gas is passed at a rate of 0.4-0.6 l / min and the absorption signal of the “cold vapor” of mercury is recorded in the form of an absorption peak using a recorder. According to the data obtained, a graph is plotted in the coordinates: mercury concentration C _Hg , (μg / ml) - peak area S (cm ² ):

S [cm ² ] = 0.35 + 380C _Hg [μg / ml] (r = 0.990), WF (5 ml aliquot)

S [cm ² ] = 0.15 + 420C _Hg [μg / ml] (r = 0.996), RP (0.5 ml aliquot)

The schedule determines the concentration of inorganic mercury in the analyzed samples of EC natural objects (table 2, 3).

The distribution in the H ₂ O — AntH — HSSA system is evaluated as follows:

- antipyrine and sulfosalicylic acid are poured into graduated test tubes per 10 ml in a volume ratio of 2: 1, i.e. in the area of liquid-phase delamination of the water-antipyrine-sulfosalicylic acid system, the necessary aliquots of the working mercury solution of 0.05 μg Hg / ml are then added, the tubes are shaken and settled for 5 minutes;

- in this case, mercury passes into the organic phase with a volume of 3 ml;

- delamination is carried out by centrifugation at 10,000 rpm (15 minutes), then the aqueous phase is separated from the organic phase and analyzed for mercury separately by the AAS hydride method (temperature of a quartz furnace 140 ° C, resonance absorption wavelength 253.7 nm);

The average degree of extraction of inorganic forms of mercury in the organic phase is (98.8 ± 0.3)% (table 1).

It is obvious that the process of mercury distribution in model electrolytes does not fully reflect extraction from real samples. Calculations using the conversion factor indicate that the degree of extraction of inorganic mercury from solid samples is close to 100%. The reason for the high efficiency is the high buffering of the organic phase (RP), prepared as described below.

A composition for extraction is prepared by mixing 100 ml of a 2.0 M aqueous solution of AntH and 50 ml of a 2.0 M aqueous solution of HSSA. In this case, the lower layer of the organic phase is formed (V = 59 ml, d = 1.7 g / cm ³ , pH of the upper aqueous phase), which is used to extract Hg from solid samples (soils, plants). The resulting amount of 59 ml is enough to prepare extracts of both soil and plants (14 samples + 2 control) • 3 ml = 48 ml. In this case, the plants are analyzed precisely by those that grew on the same soils (sample No. in tables 2, 3). Within half an hour, the mixture (AntH + HSSA) is delaminated, and a dense (about 1.7 g / cm ³ ) lower phase is formed at room temperature 25 ° С, and the preparation of the extraction reagent can be accelerated by centrifugation of the mixture of base and acid solutions. Then, weights of soils (plants) weighing 0.5000 g are placed in glass containers and 3 ml of the composition for extraction of mercury is introduced. The mixture of the sample and reagent is thoroughly mixed with a glass rod and after 30 minutes mercury is analyzed, for example, by the hydride method in 0.5 ml of organic concentrate, to which 2.5 ml of a background 0.1 M HCl solution is added, then the mercury content is determined by the resonance absorption signal (λ = 253.7 nm) of its hydride after atomization in a quartz furnace at 140 ± 5 ° C in an argon flow of 0.5 l / min, obtained by reducing an aliquot of the organic phase with an alkaline solution of sodium borohydride. The following interaction occurs with antipyrine as the base of the organic phase (RP) of the delaminating system.

AntH ⁺ + HgS (inorganic forms of mercury) = AntHg ²⁺ • HS ^- .

Organic compounds are softer than Pearson acids than inorganic, and the extraction of organo-mercury compounds is not preferable when extracting Hg forms with buffer mixture [Ant (base) + Ant Н ⁺ • SSA ^- (ionic associate - antipyrine sulfosalicylate) + Н ₂ O].

In this regard, according to acid ashing (KB, total content) and extraction (EC) of the same samples, the percentage of organic forms of mercury can be estimated (Tables 2 and 3). Such estimates are very relevant for monitoring studies of natural objects, since organic forms of mercury are considered to be much more toxic than inorganic ones. A comparison of the results presented in tables 2 and 3 allows us to calculate the percentage of organic mercury from the difference in mercury content in KB and EC. Moreover, in plants this percentage is higher (Table 3)

The implementation of the invention for selenium is achieved as follows: A series of standard solutions of selenium is prepared from a working solution of selenium 5 μg Se / ml by sequential dilution of GSO 7779-2000 selenium (IV) with a concentration of 1 mg Se / ml. Calibration dependencies are obtained immediately before measurements. As a background electrolyte, 0.1 M hydrochloric acid is used. 10 ml of background is added to the reaction flask with the necessary addition of a standard solution of selenium. From a flask with a 3% alkaline NaBH ₄ solution, a solution of 1.0 ml is displaced with argon into a analyte reactor. Argon is passed at a rate of 0.4-0.6 l / min and a signal is recorded for the absorption of selenium after atomization of its hydride in a quartz furnace at 850 ± 50 ° C in the form of a resonance absorption peak (λ = 196 nm) using a recorder. According to the data obtained, a graph is plotted in coordinates of the concentration of selenium (μg / ml) - the height of the absorption peak (cm) in the aqueous phase (WF) and organic phase (RP):

h [cm] = 1.12 + 4.46C _Se [μg / ml], (r = 0.925), WF aliquot of 5 ml

h [cm] = 1.00 + 4.30 ° C _Se [μg / ml] (r = 0.969), RP aliquot 0.5 ml

The distribution of selenium in the H ₂ O — AntH — HSSA system is evaluated as follows:

- 2 molar solutions of antipyrine and sulfosalicylic acid are poured into graduated test tubes per 10 ml in a volume ratio of 2: 1;

- add aliquots of a standard solution of selenium;

- the tubes are shaken and sedimented for 5 min, while selenium passes into the organic phase with a volume of 3 ml;

- delamination is carried out by centrifugation at 10,000 rpm (15 minutes);

- the aqueous phase (HF) is separated from the organic phase (HF) and analyzed separately for selenium AAS by the hydride method. The average degree of extraction of selenium in the organic matter was more than (92 ± 3)% (table 4).

According to the schedule for RP, the concentration of selenium in the analyzed samples of natural objects is determined (table 5, 6). It is obvious that the distribution process in model electrolytes does not fully reflect the extraction of selenium. Calculations using the conversion factor indicate that the degree of extraction from solid samples is close to 100%. The reason for the high efficiency is the high buffering of the RP. The composition for the extraction of inorganic selenium from real soils and plants is prepared as for mercury. Selenic acid (pK = 2.75) is comparable in acidity to antipyrine (pK _{H +} = 1.5). It is likely that the following interaction occurs with the base of the organic phase separation system:

Ant + H ₂ SeO ₃ (inorganic forms of selenium) = AntH ⁺ • HSeO ₃ ^- .

Organic selenium compounds, as milder Pearson acids than inorganic ones, are extracted with a hard base - antipyrine. When Se is extracted with a buffer mixture [Ant (base) + Ant H ⁺ • SSA ^- (ionic antipyrine sulfosalicylate associate)], inorganic forms of selenium are preferred as more stringent acids. In this regard, according to acid ashing (total content) and extraction of the same samples, the percentage of organic forms of selenium can be estimated (Tables 5 and 6). Such estimates are very relevant for monitoring studies of natural objects. A comparison of the results presented in tables 5 and 6 allows us to estimate the percentage of organic selenium by the difference in the selenium content in KB and EC. Moreover, in plants this percentage is higher (Table 6). The inorganic forms of selenium can be selectively separated by liquid chromatography.

Thus, the inventive method allows you to bring the process of preparing solid samples of natural objects in accordance with the requirements of "green chemistry", to avoid heating the sample and provides quantitative extraction of inorganic forms of mercury and selenium in the liquid phase, suitable for subsequent analysis of mercury and selenium by a suitable physicochemical method (atomic absorption, liquid chromatography, voltammetry).

Table 1
Hg distribution in the H ₂ O - AntH - HSSA system Introduced Hg, mcg Found Hg in WF, mcg Found Hg in RP, mcg R% 0.0025 0.00002 0,00243 99 0.005 0.00005 0,00488 99 0.010 0.00012 0.00969 99 0,025 0,00055 0,02380 98 <R> ± ε _α 98.8 ± 0.3 The total volume of the system is 10 ml: the aqueous phase is 7 ml, organic phase - 3 ml. Distribution coefficient 100-280 Note: ε _α is the confidence interval; R is the degree of extraction; in the hydride method, an aliquot volume of 5 ml of the aqueous phase (WF) and 0.5 ml of the organic phase (OF) of the exfoliating system.

table 2
Results of determination of mercury in air-dry soil samples (region of Aktash village, mercury deposit) Sample No. Hg, mcg / g % org Hg KB EC EC * F one 1.32 1.29 1.31 2 6 1.76 1,67 1,69 5 eleven 5.77 5.51 5.58 four 19 2.27 2.22 2.25 2 26 1.85 1.72 1.74 7 31 2.00 1.96 1.98 2 33 2,58 2.43 2.46 5 Note: F = (100 / 98.8) conversion factor taking into account the average degree of extraction (table 1) from model solutions; KB - acid extract with a mixture of acids: 2 ml of HNO ₃ , 1 ml of H ₂ SO ₄ , 1 ml of HCl from a sample of soil, EC - extraction from 0.5 g of soil in 3 ml of the organic phase of the stratified system,% org. Hg = [(KB-EC) * 100 / KB].

Table 3
The results of the determination of mercury in air-dry samples of plants (Aktash settlement, mercury deposit) Sample No. Hg, mcg / g % org Hg KB EC EC * R one 0.68 0.58 0.59 fifteen 6 0.79 0.71 0.72 10 eleven 0.88 0.77 0.78 12 19 1.38 1.16 1.17 16 26 0.95 0.88 0.89 7 31 1,60 1.41 1.43 12 33 1.98 1.82 1.84 8 Note:
F = (100 / 98.8) conversion factor taking into account the average degree of extraction (Table 1) from model solutions, KB - acid extract with a mixture of acids: 2 ml of HNO ₃ , 1 ml of H ₂ SO ₄ , 1 ml of HCl from a plant sample , EC - extraction from 0.5 g of soil in 3 ml of the organic phase of the exfoliating system,% org. Hg = [(KB-EC) * 100 / KB] h [cm] = 1.00 + 4.30 ° C _Se [μg / ml] (r = 0.969), 0.5 ml aliquot

Table 4
Se distribution in the H ₂ O - HAnt - HSSA system Introduced Se, mcg Found Se in WF, mcg Found Se in RP, mcg R% 0.20 less than 0.02 0.18 90 0.40 less than 0.02 0.38 95 0.80 0.04 0.72 90 2.00 0.08 1.82 91 4.00 0.12 3.74 94 <R> ± ε _α 92 ± 3 The total volume of the system is 10 ml: the aqueous phase is 7 ml, organic phase - 3 ml. Distribution coefficient 20-70 Note: ε _α is the confidence interval; R is the degree of extraction; in the hydride method, an aliquot volume of 5 ml of the aqueous phase (WF) and 0.5 ml of the organic phase (OF) of the exfoliating system.

Table 5
Results of determination of selenium in air-dry soil samples (region of Aktash village, mercury deposit) Sample No. Se, mcg / g % org Se KB EC EC * R one 7.68 7.29 7.92 5 6 8.80 8.69 9.44 one eleven 11.04 10.80 11.74 2 19 12.16 11.55 12.55 5 26 5.43 5.18 5.63 four 31 6.55 6.00 6.52 8 33 7.48 7.20 7.83 four Note: F = (100/92) conversion factor taking into account the average degree of extraction (table 1) from model solutions; KB - acid extract with a mixture of acids: 2 ml of HNO ₃ , 1 ml of H ₂ SO ₄ , 1 ml of HCl from a sample of soil, EC - extraction from 0.5 g of soil in 3 ml of the organic phase of the stratified system,% org. Se = [(KB-EC) * 100 / KB].

Table 6
The results of determination of selenium in air-dry plant weights (Aktash settlement, mercury deposit) Sample No. Se, mcg / g % org Se KB EC EC * R one 13.29 11.30 12.28 fifteen 6 9.92 9.39 10.21 5 eleven 7.58 7.18 7.80 6 19 8.88 7.98 8.67 12 26 4.31 3.77 4.10 12 31 5.43 5.10 5.54 6 33 6.55 5.89 6.40 10 Note: F = (100/92) conversion factor taking into account the average degree of extraction (Table 1) from model solutions, KB - acid extract with a mixture of acids: 2 ml of HNO ₃ , 1 ml of H ₂ SO ₄ , 1 ml of HCl from a plant sample , EC - extraction from 0.5 g of soil in 3 ml of the organic phase of the exfoliating system,% org. Se = [(KB-EC) * 100 / KB].

Claims (1)

A method of extracting inorganic forms of mercury and selenium from solid samples of natural objects, which consists in extracting mercury and selenium from the solid phase of a natural object into a liquid acid phase, characterized in that 3 are added to a sample to extract mercury and selenium from a solid sample weighing 0.5000 g , 0 ml of the dense organic phase of the water-antipyrine-sulfosalicylic acid exfoliating system, which is prepared by mixing 2M aqueous solutions of antipyrine and sulfosalicylic acid in a volume ratio of 2: 1, then the suspension is carefully per they are kneaded and after 30 minutes they are analyzed for mercury and selenium content by instrumental method.