RU2313076C1 - Method of determining mercury in water - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: invention relates to environmental analytical methods, particularly to concentrating trace element in water and aqueous solutions in order to quantitatively determining it such as it could be done with mercury. Method of invention comprises extraction of mercury from aqueous phase into organic component of stratified water-antipyrin-organic acid system and consists in introducing sample, antipyrin, and organic acid, dilution, shaking, and sampling lower phase concentrate. More specifically, 0.7-1.0 mmole sulfosalicylic acid dihydrate is added to test-tube containing 1.5-2.0 mmole antipyrin and then a snow water sample acidified with hydrochloric acid (5 mL acid per 1 L snow water) is added, total volume is brought to 10 mL, test-tube is tightly closed, contents are vigorously shaken, settled at 25°C, and centrifuged, after which 0.5 mL sample of lower organic phase concentrate is analyzed by resonance absorption technique to determine content of mercury obtained via cold vapor method after reduction with sodium borohydride.

EFFECT: enabled determination of mercury in snow water and increased accuracy of analysis.

2 dwg, 2 tbl

Description

The invention relates to the field of analytical chemistry of environmental objects, namely the concentration of a trace element from water and aqueous solutions with the aim of quantifying it using mercury as an example. As a means of measuring the mercury content in liquid objects of analysis, the flameless atomic absorption spectrometry method, the cold vapor method, was used.

A known method of atomic absorption determination of mercury in water and precipitation [G.S. Fomin. Water. Chemical, bacterial and radiation safety control according to international standards. M .: Protector, 2000. S.350-360] from 0.1 to 100 μg / dm ³ . The technique (analog) is based on the reduction of sodium borohydride with soluble forms of mercury from an aqueous solution, followed by the atomic absorption method of determining its cold atomic vapor. From snow water containing ultrafine amounts of mercury, this method does not allow reproducibly determine mercury in melt water.

Of the known technical solutions, the closest in purpose and technical essence to the claimed object is [Method for the separation of mercury from aqueous solutions (A.S. 1357759) / B.I. Petrov, S.I. Rogozhnikov, T.V. Sukhneva // B .AND. 1987, No. 45] is a prototype.

A method for separating mercury from aqueous solutions by liquid extraction of mercury from aqueous solutions using an exfoliating water-antipyrine-organic acid system.

An analyte solution is introduced into the separatory funnel containing 4-40 mg of mercury, 2.5 ml of a 2 M aqueous solution of antipyrine (Ant), 4 ml of a 10 M solution of sulfuric acid (to a concentration of 2-3 M), 5 ml of a 4 M solution of trichloroacetic acid (TCA), not containing chloride ions, diluted with water to 20 ml and shaken for 1-2 minutes, defend, then the lower phase is transferred to a flask for titration. An additional 0.5 ml of Ant solution and 1.5 ml of TCA solution are added to the funnel and shaken again for 1 min. The newly separated organic phase is poured into a flask and the mercury contained in the combined extracts is determined by known methods.

Common to the prototype and the claimed invention are the use of an exfoliating water-antipyrine-organic acid system: the claimed invention uses a pyrazolone derivative-antipyrine and organic sulfosalicylic acid.

The disadvantages of the prototype include:

- the impossibility of determining mercury in snow water (precipitation);

- the detection limit of mercury by the emission method with inductively coupled plasma is about 50 μg / L.

The essence of the proposed method for determining mercury in water is the concentration of mercury from the aqueous phase into the organic component (phase) of the stratified system H ₂ O - AntH (antipyrine) - HSSA (sulfosalicylic acid). Concentration of mercury occurs from a liquid sample (for example, snow water) in an “in situ” mode, that is, during the formation of the lower phase of the stratified system. In a glass tube for concentration with a total volume of 10 ml dry powdered substances are introduced - chemical reagents:

- 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) in quantities of 1.5-2.0 mmol and 0.7- 1.0 mmol, providing delamination into two liquid phases in a system with a single solvent - water (the rest is up to 10 ml), which is the object of analysis for mercury content, then the tube is tightly closed with a stopper and vigorously shaken for 5 minutes, standing for 15 minutes at a temperature 25 ° C, centrifuged for 5-10 min, 0.5 ml of the lower phase of the organic phase concentrate of the lower phase is taken and the mercury content is determined and the cold steam method after reduction with sodium borohydride.

The method for determining mercury in water, which consists in extracting mercury from the aqueous phase into the organic phase of the water-antipyrine-organic acid exfoliating system, which includes introducing a sample, antipyrine and organic acid, diluting, shaking and selecting an organic lower phase concentrate, characterized in that in a glass 1.5-2.0 mmol of antipyrine and 0.7-1.0 mmol of 2-aqueous sulfosalicylic acid are introduced into the tube, after which a sample is acidified with hydrochloric acid at the rate of 5 ml of acid per liter of snow water and adjusted to up to 10 ml, then the tube is tightly closed with a stopper and vigorously shaken, sedimented at a temperature of 25 ° С, centrifuged, 0.5 ml of the lower phase of the organic concentrate of the lower phase is taken and the mercury content is determined by the “cold steam” method after reduction with sodium borohydride.

The proposed method differs from the prototype in that it lowers the limits of the determined concentrations by combining in the method of liquid-phase concentration with a more sensitive in comparison with the emission method of "cold steam". The combination of these processes expands the scope of the proposed method by extraction of mercury from snow water and precipitation, characterized by ultra-low concentrations of mercury extraction. Since the content of mercury in natural objects is low, a model extraction, exfoliating system water - antipyrine - sulfosalicylic acid is used for extraction.

The implementation of the invention. Previously, the degree of mercury extraction by this system from model aqueous solutions (table 1) with GSO 7263-69 additives of the composition of mercury ions 0.95-1.05 mg / ml prepared by sequential dilution was determined by the introduced-found method. Model exfoliating systems are prepared from 2 mol / L solutions of antipyrine and sulfosalicylic acid. The optimal ratio of the volumes of such solutions of antipyrine and sulfosalicylic acid is 2: 1. The total volume of the system is 10 ml, the volume of the organic component is 1 ml. The degree of extraction of mercury in the organic component is 96.5%; 95.0%; 97%, which allows the use of an extract of the above system to extract mercury from natural snow water. The mercury signal obtained for the aqueous phase of the system is commensurate with the signal of the control (blank) experiment in the cold vapor method (about ± 0.01 ngHg / ml).

When the reagent antipyrine and organic acid (solid) are dissolved in the object of analysis (an aqueous solution containing trace amounts of mercury), an acid-base interaction occurs between the protonated antipyrine and the anions of the organic acid. The resulting organic component, consisting of an ionic associate of an organic salt, antipyrinium sulfasalicylate and antipyrine, has an acidic reaction and extracts mercury hydroxochlorides from acidic chloride solutions due to the formation of a complex metal complex with an ionic and organic in nature liquid. The volume of the organic component (lower phase) in the presented range of chemical reagent compositions varies from 1 to 3 ml, and a change in the molar amounts of reagents for the indicated composition interval causes at 25 ° C in violation of the conditions of liquid-phase separation and the formation of monotectic phases of variable composition (transparent crystals, isotherm solubility) [B.I. Petrov, S.A. Denisova, A.E. Leonov, G.E. Shestakova. Interphase distribution of some elements in the water-antipyrine-naphthalene-2-sulfonic acid system // News of universities. Chemistry and Chem. technology. 1999. Vol. 42, No. 1. S.21-23, Fig. 1]. The end of the analytical procedure consists in determining the mercury content by the “cold steam” method after reduction with sodium borohydride. The results presented in table 1 for the organic component of the system (1 ml) are obtained by atomic absorption method with the restoration of all forms of mercury with an alkaline 3% sodium borohydride solution (1 ml) against a background of 0.1 mol / L HCl (1 ml) followed by atomization of mercury in a quartz furnace (140 ° C) in a stream of argon. In the future, the AA method of cold steam is used as independent for the calibration of the inventive electrochemical method. When analyzing real samples of snow cover, the following preliminary preparation is implemented. Snow cores (diameter 3.2 cm and height 60-70 cm) are selected for 5 pieces for each point (7 pieces, table 2). Samples are combined and thoroughly mixed and delivered to the laboratory in frozen form. Under laboratory conditions, samples are thawed under natural conditions and filtered (snow water) in an argon atmosphere through nuclear membrane filters with a pore diameter of 0.11 μm, which makes it possible to obtain a filtrate of snow mass free of colloidal dispersed particles of natural and anthropogenic aerosols - the main carriers of mercury. The thus obtained snow filtrate is acidified with hydrochloric acid at the rate of 5 ml of acid per liter of snow filtrate. Then, dry AntH and HSSA samples were added to the extraction tube and the total volume was adjusted to 10 ml with the analyzed snow water filtrate. Shake the tube thoroughly for 5 minutes, assert at 25 ° C for 15 minutes to form the lower phase of the organic component and centrifuge for 5-10 minutes. Next, take an aliquot of the lower phase of an ionic organic liquid with a volume of 0.5 ml and add to the hydride prefix, add 1 ml of 0.1 mol / L hydrochloric acid and include argon (50 ml / min). Under an argon pressure, 1 ml of an alkaline 3% sodium borohydride solution in the presence of 0.1 mol / L HCl (1 ml) enters the reaction vessel with an aliquot containing mercury, atomization of mercury occurs, the so-called “cold vapor” in a quartz furnace (140 ° C) and resonant absorption of characteristic radiation by the "cold vapor" of mercury. A hollow cathode mercury lamp (analytical line 253.7 nm) is used as a radiation source. Build a calibration schedule (figure 2). The determination results are presented in Table 2. The minimum concentrations of mercury determination thus established of 0.0084 ± 0.0002 μg Hg in a liter of snow water are representative, determined in 10 ml of the object and correspond to a volume concentration of approximately 10 times. Even in the snow of urban areas, dissolved forms of mercury are contained in such small quantities that for their determination it is necessary to apply additional concentration using the proposed method. The direct method of “cold steam” without concentration does not give satisfactory reproducible results.

Table 1 Metrological characteristics of the stratified extraction system water - antipyrine - sulfosalicylic acid Introduced Hg, mcg Found Hg, mcg R% 0.00250 0.00240 96.5 0,00237 95.0 0,00243 97.0 <value> ± ε _α 0.00240 ± 0.0001 96 ± 4

Note: ε _α is the confidence interval; R is the degree of extraction, the total volume of the system is 10 ml. The volume of the organic component is 1 ml. Aliquot for the method of "cold steam" 0.5 ml.

table 2 The results of the determination of Hg by the method of "cold steam" in the melt water filtrate after liquid extraction of H ₂ O-AntH-HSSA. Melt
Water Sample number C _Hg , mcg / L The aqueous phase (upper phase) OK (upper phase) <C _Hg > ± ε _α Conditionally background level one
2
3 <0.01
<0.01
<0.01 0.0087 ± 0.0002
0.0084 ± 0.0001
0.0085 ± 0.0002 0.0084 ± 0.0002 Urban snow cover four
5
6
7 <0.01
<0.01
<0.01
<0.01 0.016 ± 0.004
0.014 ± 0.002
0.018 ± 0.002
0.014 ± 0.001 0.016 ± 0.003

Claims (1)

A method for determining mercury in water, which consists in extracting mercury from the aqueous phase into the organic component of the water-antipyrine-organic acid exfoliating system, comprising introducing a sample, antipyrine and an organic acid, diluting, shaking and selecting an organic lower phase concentrate, characterized in that in a test tube 1.5-2.0 mmol of antipyrine and 0.7-1.0 mmol of 2-aqueous sulfosalicylic acid are added, after which a sample is acidified with hydrochloric acid at the rate of 5 ml of acid per liter of snow water and the total volume is adjusted volume up to 10 ml, then the tube is tightly closed with a stopper, vigorously shaken, sedimented at a temperature of 25 ° С and centrifuged, 0.5 ml of the organic concentrate of the lower phase is taken and the mercury content obtained by the cold steam method after reduction with sodium borohydride is determined by resonance absorption.

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