Method of determining microconcentrations of antimony in natural waters for environmental monitoring

FIELD: analytical methods in environmental monitoring.

SUBSTANCE: method comprises: sampling, acidifying samples with HCl/H2SO4 mixture, adding Ce(SO4)2 as oxidant and removing its excess with reducing agent NH2OH·HCl, adding rhodamine C as organic reagent, extracting resulting complex, separating organic phase from aqueous phase, and measuring optical density. Extraction is performed with carbon tetrachloride/methyl isobutyl ketone mixture at 5:1 volume ratio and extractant-to-sample volume ratio 1:1 under dynamic conditions by way of washing away complex with extractant. Content of antimony is judged of from difference of optical densities of extractant and mixture.

EFFECT: lowered measurement threshold to values comparable with allowable limits, increased reliability, reduced analysis time, and automated analytical procedure.

3 cl, 1 dwg, 3 tbl, 3 ex

 

The invention relates to chemical methods of analysis of trace and can be applied in analytical chemistry and ecology, in particular, to determine the trace of antimony in waters waters for chemical monitoring.

Antimony is among the relatively widespread pollutants in natural waters, because of the wide use of its compounds in agriculture and industry. MAC antimony in water for sanitary-hygienic standards is 50 micrograms/l [1], which imposes the relevant requirements on the methods of its determination in water.

Known methods for determining the concentrations of antimony, based on the ability of antimony to form colored complexes with inorganic anions [2]. Known methods are quite time-consuming, are not sufficiently low detection limits.

Known methods of determination of antimony based on the use of inorganic reagents that can form a colored compound with antimony for the extraction of antimony was proposed allocation in the form of hydride [3]. The formation of hydride includes the recovery of a sample in an acid solution and transportation of hydride in the absorber, after the separation of the antimony in the form of hydride maybe its definition with one of the basic dyes.

In the basis of the method was based on Tverdov is knowing the reaction chrome I pyrazole (4-dimethylaminophenyl-4-methylbenzylamine-carbinol) with production by iodide complex of antimony (III), education iodide complex occurs when the absorption of STIBINE acidic solution of a mixture of iodine and iodide, the process of kompleksoobrazovanija should the Association iodide complex Sb (III) and chromium-pyrazole I.

The proposed method involves the formation of STIBINE - poisonous substances that can cause hemolysis (the disintegration of blood cells), which is a disadvantage of the method.

There is a method of determining the concentrations of antimony, based on a principle similar to that proposed, the definition of the concentration of antimony in the optical density of the resulting anionic associate, which is proportional to the antimony content in the sample. Extraction of associate produced using benzene or isopropyl ether. For a fairly complete transfer of Sb(III) in the form of associate is required oxidizing environment with a high concentration of hydrochloric acid (not less than 6 mol/l). As the oxidant most suitable Ce(IV). To destruction the excess cerium is used hydrochloric acid hydroxylamine. The method is carried out in a static mode [4].

The disadvantage of this method is its low enough detection limit, low reliability, duration analysis, as well as its toxicity for researchers and the environment, as as extractant used benzene - matter of the second class of danger. Offer is as a solvent of isopropyl ether are not able to stay on a column of polytetrafluoroethylene, that excludes the possibility of its use for the concentration of associate. The claimed invention is devoid of these shortcomings.

The technical result of the claimed invention is to improve the limit of detection, reliability, and security determine trace of antimony in waters waters for environmental monitoring, as well as for laboratory tests, in particular, in analytical chemistry and ecology. In addition, the analysis process is much faster due to its automation when using flow-injection analyzer.

Unlike the prototype in the claimed invention instead acidification 6-molar solution of Hcl used a mixture of acids, and the extractant is a mixture of organic solvents.

The proposed method differs from others in that it uses a safer reagents, selected in such relation with respect to each other and to the sample, which makes possible the automation of the analysis for flow-injection option.

The technical result of the automation of the analysis is due to the fact that instead of the earlier proposed 6-molar hydrochloric acid using a mixture of hydrochloric and sulphuric acids, which allows for analysis in flow-injection version. The higher detection limit is due to the fact that in the ode analysis is the concentration of associate rhodamine With hexachlorobuta on extraction chromatographic column with polytetrafluoroethylene as a filler and with the extractant as the stationary phase.

The essence of the method is illustrated with specific examples, are summarized in tables 1, 2, 3.

Table 1 shows that the distribution coefficient of antimony in the form of associate of hexachlorobuta with rhodamine With system 6-molar HCl - extractant for extracting agent composition of carbon tetrachloride - methyl-isobutylketone (volume ratio 5:1) numerically superior to those for other common organic solvents. The choice of the composition of the extractant was conducted in the preliminary experiment on the model solutions. All further studies were made using found extractant.

Table 2 shows the influence of the composition of the aqueous phase on the distribution coefficients of associate of hexachlorobuta with rhodamine C. it is Seen that the distribution coefficients of associate if his education in the environment of 6 molar HCl and a mixture of 2-molar HCl + 2-molar H2SO4(1:1) differ slightly. Checking the completeness of the transition of antimony in associat was carried out according to parallel experiments in 6-molar HCl and mixed HCl+H2SO4the solution, followed by extraction in selected extractant. The use of a mixture of acids enables analysis in flow-injection version, because the device for analysis is exposed to a lower risk of being damaged.

Pre the proposed method was tested in one of the chemical laboratories at the St. Petersburg state University. One example implementation of the method is illustrated in the drawing, which shows a diagram of the flow-injection determination of antimony and specially selected conditions of its extraction selection, which includes: the peristaltic pump (1); vial of extractant (2); valve switch (3); - extraction-chromatographic column (4); chromatomembrane cell (5); flow-photometric detector (6); a stream of distilled water (a); sample stream (b); the flow of the mixture of the acid (V); the flow of the hydrochloric acid solution of cerium (g); the flow of a solution of hydroxylamine (l); flow solution of rhodamine S (e); the line of discharge of the aqueous phase (W); line reset organic phase (h); line reset sample (s).

As can be seen from the drawing, the flow of the sample and the solutions generated by the peristaltic pump (1), going through a two-position valve switch (3). In the first position corresponding to the dotted lines on the tap switch on extraction-khromatograficheskoi column with polytetrafluoroethylene as a carrier of the organic phase (4) is allocated [SbCl6]-·PC. The stream samples (b) sequentially mixed with HCl+H2SO4(4 mol/l HCl + 4 mol/liter of H2SO4) (), Ce(SO4)2(0.01 mol/l to 2 mol/liter of H2SO4) (g), NH2OH· HCl (0,03%) (e) sootnoshenie the x 2:2:0,5:2:2, defined costs through appropriate channels of the pump.

To create a flow of extractant used pressure vessel (2), which filed a stream of distilled water at the rate of 2 milliliters/minute. Displaced from the vessel extractant in the first position tap switch, bypassing the extraction-chromatographic column, is sent to the chromatomembrane cell (5) and later in the supply photometric detector (6). On the display screen of the analyzer PIA-CON" when this is prescribed line of the background signal corresponding to "zero" concentration of antimony in the extractant.

In the second position of the valve switch corresponding to the solid lines in the diagram of the crane switch, the sample is sent to the reset (and), and displaced from the vessel extractant aluinum of extraction-chromatographic column associat [SbC6]-·RS. The eluate in the chromatomembrane cell is separated from displaced from the column of the aqueous phase and is directed to the detector. Because chromatomembrane process requires that the pressure of the polar phase in the entire volume of mass transfer space exceeded the pressure of the non-polar phase, level drain polar phase (W) at the output of the cell is set above the level of the extractant (C). The presence in the eluate of associate [SbCl6]-·PC causes a change in the opt is achieved density, that peak is registered by the detector. The optical density of the solutions was measured on a spectrophotometer SPEKOL-21, λ =540 nm, I=10 mm

Test was conducted on sample real natural water, the results of which are presented in table 3 and are reflected in examples 1-3, each of which was used volume of sample natural water 20 ml.

Example 1. Selection of the composition of the extractant. For extraction excretion of antimony in the form [SbCl6]-·PC recommended composition of the aqueous phase - 6 mol/l HCl. In the preliminary experiment on the model solutions [SbCl6]-in 6 mol/l HCl selection of the composition of the extractant, enabling extraction-chromatographic excretion of antimony in the form of associate [SbCl6]-·PC.

To determine the distribution coefficients of antimony in the form of associate its chloride complex with rhodamine ([SbCl6]-·PC) in static conditions used the method of re-extraction. The ratio of the volumes of the sample and extractant was 1:1. Conditions for extraction-chromatographic determination of antimony was created according to [4], which in the separating funnel was made 10 ml of 0.5 mg/l solution of Sb (III) in a 6 molar HCl and 0.1 molar solution of cerium sulfate, are thoroughly mixed for 10 minutes at room is based temperature to complete the oxidation of Sb (III) to Sb (V). Then added 0.1 ml of a 1%solution of hydrochloric acid hydroxylamine for recovery of excess cerium. For the formation of extractable compounds were made in 0.5 ml of 0.2%rhodamine and With 10 ml of extractant, then mixed with extractor PE-8020 (1 min, 500 rpm) ("NPO ECROS", St. Petersburg). Separating the organic phase from the water and then they were re-extracted with the same volume of extractant. According to the results of spectrophotometric analysis of the calculated distribution coefficients (Kd): Kd=A1/A2where A1and A2optical density of the first and second extracts, respectively. As can be seen from table 1, the conditions obtained for easily available solvent mixture: methyl-isobutylketone - carbon tetrachloride (1:5). All subsequent studies were performed using found extractant.

Example 2. Investigation of the influence of acidity. To obtain maximum yield of the colored product was studied the influence of HCl concentration. We studied the possibility of creating the conditions PIA necessary acidity using mixed in volumetric relationship HCl+H2SO4solutions. The volume ratio of the mixture of acids and samples 1:1. Checking the completeness of the transition of antimony in associat [SbCl6]-·PC was carried out on Yes the th parallel experiments in 6 mol/l HCl and mixed HCl+H 2SO4the solution, followed by extraction in selected extractant. It is established that from a solution of 2 mol/l Hcl + 2 mol/l H2SO4antimony is extracted almost as effectively as of 6 mol/l (table 2).

Example 3. Determining the concentration of antimony in natural water. Determining the concentration of antimony in natural water produced by the method introduced is found. Standard solution of antimony concentration 1 g/l were prepared by dissolving accurately weighed Sb2O3in 100 ml of 6 mol/l hydrochloric acid, followed by diluting the solution to 1 l of hydrochloric acid with a concentration of 1 mol/L. the resulting solution was standardized by iodometric titration [6]. As the working solutions used 0,03% solution of hydrochloric acid hydroxylamine, and a 0.04% solution of rhodamine C. a Solution of Ce(SO4)2with a concentration of 0.5 mol/l was prepared by dissolving 5 grams of CE(SO4)2·H2O in 1 liter with 6 mol/l sulfuric acid.

Methyl-isobutylketone, carbon tetrachloride, cyclohexane, nitrobenzene, dimethylformamide, dichloroethane was used without additional purification. So, with the introduction of 10 micrograms of antimony was found to 10.4 micrograms, therefore, it is possible to judge the presence of 0.4 micrograms of antimony in the water sample with an average standard deviation of 0.02. With the introduction of 20 micrograms found 20,3 m is crogram, therefore, in a sample of water contains 0.3 micrograms of antimony with an average standard deviation of 0.01.

The proposed method is compared with the prototype shows a lower limit of detection, higher reliability, security analysis, and the possibility of automation of the process, which significantly reduces the time for analysis. All this allows you to successfully use the proposed method in analytical chemistry and ecology, in particular, to determine the trace of antimony in waters waters for environmental monitoring.

THE SOURCES OF INFORMATION.

1. Control chemical and biological parameters of the environment/Ed. by Isaeva L.K. St. Petersburg: "Christmas+", 1998, p.160.

2. Nemotek A.A. Analytical chemistry of antimony. M.: Nauka, 1978, p.41.

3. Kolesnikov A., Lazarev A. I. Spectrophotometric determination of antimony using chrome I pyrazole after separation in the form of a hydride.//EACH. 1971. So 48. Vol. 9, s.

4. Nemotek A.A. Analytical chemistry of antimony. M. Nauka, 1978, p.50.

5. Talipov ST, Jienbaeva A.D., Abdishev AV photometric determination of antimony (III) 4-(2-N-methylaniline)-resorcinol.//GAH, 1972, 27 So. Vol. 8, s.

6. Nemotek A.A. Analytical chemistry of antimony. M.: Nauka, 1978, p.7.

94
Table 1
The extractantKdSr
Carbon tetrachloride-dichloroethane (5:1)20,06
Carbon tetrachloride-dimethylformamide (5:1)20,05
Carbon tetrachloride-nitrobenzene (5:1)230,04
Carbon tetrachloride-cyclohexanone (5:1)350,03
Carbon tetrachloride-methyl-ISO-butylketone (5:1)880,02
Table 2
The composition of the aqueous phaseTodSr
6 mol/l HCl970.01
1 mol/l HCl + 3 mol/liter of H2SO4320.05
a 1.5 mol/l HCl + 2.5 mol/liter of H2SO4600.02
2 mol/l HCl + 2 mol/liter of H2SO40.01
Table 3
Introduced Sb(III), microgramsFound Sb(W), microgramsSr
10,010,40,02
2020,30,01
8,48,60,05

1. The method for determining trace of antimony in natural waters for environmental monitoring of water areas, including sampling, acidification its mixture of acids Hcl and H2SO4the addition of Ce(SO4)2as oxidant and removing the excess reducing agent NH2HE·Hcl, adding With rhodamine as the organic reagent and the subsequent extraction of the complex formed, separating the organic phase from the water and measuring the optical density, characterized in that as a solvent, a mixture of carbon tetrachloride with methyl-isobutylketone taken in the ratio of 5:1, when the ratio of the extractant and the sample 1:1, extraction of the formed complex is carried out in a dynamic mode by flushing complex with the extractant, and the antimony content is judged by the difference of the optical density of the extractant and with whom thou.

2. The method according to claim 1, characterized in that the Hcl and H2SO4taken in the ratio of 1:1 with respect to their mixtures and samples 1:1, and the concentration of acid is 2 mol/L.

3. The method according to claim 1, characterized in that as a solvent, a mixture of carbon tetrachloride and methyl-isobutylketone taken in relations 5:1 between a and 1:1 in relation to the sample.



 

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