RU2370760C1 - Method of detecting uranium (vi) in solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: buffer mixture is added to an analysed solution, containing uranium (VI), and voltammetric determination is done while plotting current versus voltage curves, with subsequent determination of content of uranium (VI) from the height of peak of the curve. The background electrolyte is a mixture of 1-6 ml organic high-solvating solvent, 5-12 ml buffer mixture (with concentration 1-5M). Distilled water is added to the obtained solution up to 25 ml volume, after which a cathode curve is plotted for voltage ranging from 0.5 to -1.8 V, and concentration of uranium (VI) is determined from the height of the peak.

EFFECT: increased selectivity and accuracy of qualitative and quantitative determination of concentration of uranium in a solution, reduced absolute amount of substance required for analysis, possibility of detecting uranium in objects with complex composition in the presence of concomitant ions which disturb detection under normal conditions.

7 cl, 4 ex, 5 tbl

Description

The proposed method relates to the field of analytical chemistry, in particular to methods for measuring the concentration of uranium (VI) in solutions, and can be used to analyze complex composition solutions containing uranium (VI) ions. The invention is applicable in environmental control systems and technological processes.

Known voltammetric method for the direct determination of uranium (VI). In this method, the determination is carried out using 0.1 M potassium thiocyanate and 0.001% gelatin as a background electrolyte at a pH of 2.5 ± 0.1. An aliquot of the sample is diluted with a background electrolyte, a pH of 2.5 ± 0.1 is set, the resulting working solution is placed in an electrolytic cell and deaerated with nitrogen for 15 minutes, after which the cathode wave is recorded in the potential range of -0.1 - -0.4 V. The uranium concentration is determined by its height cathode peak (clearly manifested at a potential of -0.26 V). A mercury dripping electrode is used as the working electrode. The minimum detectable concentration is 2.4 mg / L. [Tamrakar R. K., Pitre K. S. Voltammetric trace analysis of uranium and other metals in meta rhyolite rock samples. / Analytical sciences 951-955, 2000.]

The voltammetric method for determining uranium (VI) with cupferron in sea water is described. For determination, acetate buffer solution (pH 4.2) and cupferron are added to the analyzed sample. Potentiometric determination is carried out without deaeration with preliminary accumulation of the uranium (VI) complex with cupferron for 180 s at a potential of -0.65 V. The concentration of uranium is determined by the height of its cathode peak. As a working electrode, a film lead electrode is used. This method allows to determine uranium (VI) in the concentration range of 5 × 10 ^-10 -2 × 10 ^-8 mol / L. [Korolczuk M., Tyszczuk K., Grabarczyk M. Determination of uranium by adsorptive stripping voltammetry at a lead film electrode. / Talanta, V.72, 2007. P.957-961.]

The objective of the invention is to increase the selectivity and accuracy in the qualitative and quantitative determination of the concentration of uranium (VI) in solution, reduce the absolute amount of the substance needed for analysis, the ability to determine uranium in complex objects in the presence of concomitant ions that interfere with the determination under ordinary conditions.

The introduction of an organic solvent with a high solvating ability into the analyzed systems leads, as a rule, to a shift of the peak potentials to more negative or more positive values and to a change in the values of the limiting currents. Experimental studies have shown that the presence of solvents with a high solvating ability in complex composition systems containing uranium (VI) ions and its attendant elements leads to an increase in selectivity and accuracy of determination (Table 1). In this case, the effect of interfering with the determination of ions is leveled.

Dimethyl sulfoxide is used as a solvating organic solvent, and a solution of aminoacetic acid, hydrochloric acid and sodium chloride is used as a buffer mixture.

Example 1. The definition of uranium (VI).

An aliquot of the analyzed solution from 0.1 to 5 ml is added to a 25-ml volumetric flask depending on the uranium content in the test mixture, 10 ml of 1-5 M aminoacetic buffer mixture are added, 1-6 ml of highly solvating organic solvent (dimethyl sulfoxide) is diluted to the mark with distilled water, mix thoroughly and deaerate with nitrogen for 5 minutes. An aliquot of 5.0 ml is placed in an electrochemical cell, the working and auxiliary electrodes are immersed in the solution, and voltammetric determination is carried out with the voltammogram recorded in the potential range from 0.90 to -1.6 V. The uranium (VI) content is found by the height of its cathode peak (Table 2). A silver amalgamated electrode is used as the working electrode.

Example 2

The same as example 1, except that dimethylformamide was used as a highly solvating organic solvent (Table 3).

Example 3

The same as example 1, except that instead of a buffer mixture, a 1-5 M buffer mixture of succinic acid and sodium tetraborate is used (Table 4).

Example 4

The same as example 3, except that dimethylformamide is used as a highly solvating organic solvent (Table 5).

Since dimethyl sulfoxide and dimethylformamide are similar in their characteristics and have a similar effect, they can be interchangeable reagents that extend the limits of conventional voltammetric determination and increase its sensitivity and accuracy.

Table 1 Relative indicators of accuracy (m) and selectivity (ΔЕ) of voltammetric determination of uranium (VI) in the studied systems No. nn System m = D / D _op ΔE = EE _op , mV one uranium (VI) - succinic acid - sodium tetraborate - DMSO 1,2 320 2 uranium (VI) - succinic acid - sodium tetraborate - DMF 1,2 390 3 uranium (VI) - aminoacetic acid - sodium chloride - sodium tetraborate - DMSO 1,5 250 four uranium (VI) - aminoacetic acid - sodium chloride - sodium tetraborate - DMF 1.7 280

table 2 Determination of uranium (VI) in model solutions of aminoacetic acid - hydrochloric acid - sodium chloride - dimethylformamide Experience number With _{U (VI)} × 10 ⁻⁴ mol / L, administered With _{U (VI)} × 10 ^-4 mol / L, determined Error,% one 1.00 0.99 1,0 2 2.00 1.99 1.7 3 4.00 3.98 4.7 four 8.00 7.98 1,0

Table 3 Determination of uranium (VI) in model solutions of aminoacetic acid - hydrochloric - sodium chloride - dimethyl sulfoxide Experience number With _{U (VI)} × 10 ⁻⁴ mol / L, administered With _{U (VI)} × 10 ^-4 mol / L, determined Error,% one 1.00 0.95 4.7 2 2.00 1.95 2,3 3 4.00 3.86 3.6 four 8.00 7.8 2.5

Table 4 Determination of uranium (VI) in model solutions of succinic acid - sodium tetraborate - dimethyl sulfoxide Experience number With _{U (VI)} × 10 ⁻⁴ mol / L, administered With _{U (VI)} × 10 ^-4 mol / L, determined Error,% one 1.00 0.96 3.8 2 2.00 1.96 1.9 3 4.00 3.89 2,8 four 8.00 7.68 4.0

Table 5 Determination of uranium (VI) in model solutions of succinic acid - sodium tetraborate - dimethylformamide Experience number With _{U (VI)} × 10 ⁻⁴ mol / L, administered With _{U (VI)} × 10 ^-4 mol / L, determined Error,% one 1.00 0.96 4,5 2 2.00 1.97 1,6 3 4.00 3.92 2.0 four 8.00 7.76 3.0

Claims (7)

1. The method for determining uranium (VI) in solutions, which consists in adding a buffer mixture to the analyzed solution containing uranium (VI), immersing working and auxiliary electrodes in the solution, and performing voltammetric determination with registration of current-voltage curves, followed by determination of the content uranium (VI) by the height of its peak on the curve, characterized in that a silver amalgamated electrode is used as the working electrode, then 1-6 ml of highly solvating organic solvent is added, 5-12 ml of b of a spherical mixture with a concentration of 1-5 M and bring the volume of the resulting solution with distilled water to 25 ml, after which a cathodic curve is recorded in the potential range from 0.5 to -1.8 V, while the concentration of uranium (VI) is determined by the height of its peak. 2. The method according to claim 1, characterized in that dimethyl sulfoxide is used as a highly solvating organic solvent. 3. The method according to claim 1, characterized in that dimethylformamide is used as a highly solvating organic solvent. 4. The method according to claim 2, characterized in that as a buffer mixture use 1-5M buffer mixture of succinic acid and sodium tetraborate. 5. The method according to claim 2, characterized in that as a buffer mixture using 1-5M buffer mixture of aminoacetic acid, sodium chloride and hydrochloric acid. 6. The method according to claim 3, characterized in that as a buffer mixture use 1-5M buffer mixture of succinic acid and sodium tetraborate. 7. The method according to claim 3, characterized in that as a buffer mixture using 1-5M buffer mixture of aminoacetic acid, sodium chloride and hydrochloric acid.