RU2291421C1 - Indicator composition for determining silver(i) in aqueous solutions - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: indicator composition for determining silver(I), in particular, in waste and production solutions containing dithizone in the form of 0.001% alcohol solution (0.003 wt % of solution) and water additionally contains, as sorbent, anionite AN-25 in thiocyanate form (2.0 wt %).

EFFECT: increased determination rapidity and extended determinable silver(I) concentration range.

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Description

The invention relates to analytical chemistry (indicator compositions) and can be used to determine silver (I) in aqueous solutions, in particular, in waste and industrial solutions.

To determine silver (I) in solutions, spectrophotometric methods using organic reagents are widely used, among which compounds containing nitrogen and sulfur atoms [Pyatnitsky I.V., Sukhan V.V. - M .: Nauka, 1975. - 350 p.]. Most of these methods involve masking, extraction, and other separation methods. The use of reducing agents, stabilizers, and organic solvents is often required to obtain an analytical signal. All this complicates the analysis, complicates and lengthens the operation, and the extraction requires special safety rules, since it is associated with the use of toxic organic solvents (chloroform, diethyl or isopropyl ether, benzene, carbon tetrachloride).

Known indicator composition for extraction-photometric determination of not more than 80 μg of silver with dithizone in a solution of carbon tetrachloride [Marchenko Z. Photometric determination of elements. - M .: Mir, 1971. - 508 p.] (Prototype).

The disadvantages of the technical solution include the large time costs associated with conducting multiple extraction, as well as the inability to use this technique with silver (I) contents of more than 80 μg.

The low silver content in natural and industrial facilities requires an increase in the sensitivity and selectivity of reactions. For this purpose, indicator compositions are used, including various sorbents, which allows the determination of silver in the sorbent phase.

The technical result of the invention is to increase the expressivity of determination and the expansion of the range of detectable concentrations of silver (I).

The technical result is achieved by the fact that in the indicator composition for determining silver (I) in aqueous solutions, containing dithizone in the form of a 0.001% alcohol solution and water, additionally contains as an sorbent anion exchange agent AN-25 in thiocyanate form with the following component content, wt.% :

Anion exchanger AN-25 in isocyanate form 2.0 Dithizone as a 0.001% alcohol solution 0.003 Water Rest

To determine the sample of the analyzed solution with a volume of 10.0 ml, it is placed in a graduated tube with a ground stopper with 0.2 g of pre-swollen AN-25 anion exchange resin in isocyanate form and shaken for 20 minutes. Then the ion exchanger is filtered off, 10.0 ml of a 0.001% alcohol solution of dithizone are added to it and again shaken for 10 minutes. After that, the ion exchanger is filtered off and the diffuse reflectance of the wet sample is measured at a wavelength of 670 nm on a Pulsar colorimeter with respect to the reference sample, which is the indicator composition described above without silver (I).

The silver (I) content in the analyzed solution is calculated according to the calibration schedule, for the construction of which aliquots of a standard silver nitrate solution with an Ag (I) content of 10 dl to 200 μg are taken, and then proceed as described above.

The diffuse reflection coefficient is converted into the Gurevich – Kubelka – Munk function by the equation:

где

Where

R and R ₀ are the diffuse reflection coefficients of the reacted sample and the reference sample, respectively.

The dependence is built in the coordinates ΔF (R) -C _{Ag (I)} , where C _{Ag (I)} is the concentration of silver (I) in the solution.

The introduction of AN-25 anion exchanger into the indicator composition makes it possible to increase the expressivity of determination, and the use of the isocyanate initial form of this anion exchanger broadens the range of detectable silver (I) concentrations and increases the selectivity of determination (Table 1). Sorbent AN-25 is a polyvinyl weakly basic anion exchange resin with functional tertiary amino groups [A. Lurie Chromatographic materials. - M .: Chemistry, 1978. - 439 p.]. To obtain the initial isocyanate form of the AN-25 anion exchange resin after conventional conditioning of a commodity ion-exchange resin by treatment with 1-2 M solutions of hydrochloric acid and sodium hydroxide, the sorbent is washed with distilled water to a neutral medium and saturated with 1 M potassium thiocyanate solution. After that, the sorbent is washed with distilled water from excess KSCN, dried in air and stored in bottles with ground stoppers for a long time (up to three years). The determination of silver (I) does not interfere with 1000-fold excesses of sodium, potassium and magnesium, as well as single excesses of cobalt (II), copper (II), nickel (II) (Table 2). The presence of the latter ions in large quantities can be masked with ethylene diamine tetraacetic acid (EDTA).

The reproducibility of the methodology with the developed indicator composition was verified by the “introduced-found” method in determining silver (I) in model solutions (Table 3).

Thus, the operation of concentrating silver (I) on the AN-25 anion exchange resin in the SCN ^- - form allows one to increase the expressivity of determination and expand the range of detectable silver concentrations. It should be noted that silver thiocyanate complexes are highly stable [Lurie, Yu. Yu. Handbook of analytical chemistry. - M .: Chemistry, 1979. - 480 p.], Which allows the determination of silver (I) in acidic solutions without interfering influence of chloride ions.

^* Model solutions are solutions of AgNO ₃ in the appropriate concentration of silver (I)

Claims (1)

The indicator composition for determining silver (I) in aqueous solutions containing dithizone and water, characterized in that it contains dithizone in the form of a 0.001% alcohol solution and additionally contains anion exchange agent AN-25 in thiocyanate form as the sorbent with the following components, wt.%: Anion exchanger AN-25 in isocyanate form 2.0 Dithizone in the form of a 0.001% alcohol solution 0.003 Water Rest