RU2456592C1 - Method of determining cobalt (ii) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves preparation of a cobalt (II) solution, extraction of cobalt (II) from the solution using a sorbent, conversion thereof into a complex compound on the surface of the sorbent, separating the sorbent from the solution, measuring colour intensity of the surface cobalt complex and determining content of cobalt, wherein the sorbent used is silica which is successively modified polyhexamethylene guanidine and a nitroso-N-salt, and colour intensity is determined from the diffuse reflection factor which is measured at 540 nm.

EFFECT: high sensitivity and information content of analysis.

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Description

The invention relates to the field of analytical chemistry of elements, namely to methods for the determination of cobalt, and can be used in its determination in technological solutions and industrial waters.

To determine cobalt in objects of various compositions, the sorption-photometric method is used, based on the separation of an element from a solution and its determination directly in the sorbent phase. The sorption-photometric method is characterized by low detection limits and high selectivity due to the sorption concentration of the element being determined and its separation from interfering components.

To implement the sorption-photometric determination of cobalt (II), it is necessary that a colored cobalt (II) compound with functional groups of the sorbent is formed during sorption, and the color of the sorbent increases proportionally with an increase in the concentration of cobalt (II) on the surface of the sorbent.

A known method of sorption-photometric determination of cobalt (II) [Ivanov V.M., Kuznetsova O.V. Immobilized 4- (2-thiazolylazo) resorcinol as an analytical reagent. Test reactions for cobalt, palladium and uranium (IV) // Journal of analytical chemistry. 1995.V.50. No. 5. S.498-504], based on the separation of cobalt from solutions by a sorbent - silica gel, chemically modified with 4- (2-thiazolylazo) resorcinol (SG-TAP) and its determination directly on the surface of the sorbent by the photometric method.

The method involves the following operations:

- a cobalt (II) solution was introduced into a graduated tube with a capacity of 15 ml;

- 5 ml of buffer solution was added to create a pH of 6.2 and water to a total volume of 15 ml;

- 0.3 g of sorbent SG-TAP was added and mixed vigorously;

- the sorbent was separated from the solution by decantation, dried in air, and the cobalt content on the surface of the sorbent was determined by the photometric method.

The linearity range of the calibration graph is maintained in the range of 2-15 μg cobalt in 15 ml or, accordingly, 2-15 μg per 0.3 g of sorbent.

The disadvantages of the method include a high detection limit, a narrow range of detectable contents.

A known method of sorption-photometric determination of cobalt using silica chemically modified with triphenylphosphonium groups [Dyachenko N.A., Trofimchuk A.K., Sukhan V.V. Sorption of cobalt in the form of a complex with nitroso-P-salt of silica gel with grafted triphenylphosphonium groups and its subsequent determination in the sorbent phase // Journal of Analytical Chemistry. 2002.V. 57. No. 11. S.1202-1205], providing for the following operations:

- introduction into a solution containing cobalt of a reagent - nitroso-P-salt;

- bringing the pH of the solution to 7-8.5 using KOH;

- the addition of silica modified with triphenylphosphonium groups;

- sorption for 15 minutes;

- separation washing and drying the sorbent;

- measurement of the diffuse reflection coefficient at 520 nm.

This method will allow you to determine the concentration of cobalt in the range of 0.5-10 μg in 200 ml using a weighed sorbent of 0.3 g. The lower limit of the determined cobalt contents is 2.5 μg / L.

The disadvantages of the method include a narrow range of detectable contents, multi-stage determination, a narrow pH range, inaccessibility of the proposed sorbent - silica, chemically modified with triphenylphosphonium groups.

Closest to the proposed method in technical essence and the achieved results is a method of sorption-photometric determination of cobalt (II) using silica sequentially modified with polyhexamethylene guanidine and 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-P-salt) [patent RF №2374638, IPC G01N 31/22, publ. 11/27/09].

The method includes the following operations:

- sorbent preparation based on sequential processing of silica with aqueous solutions of polyhexamethylene guanidine and nitroso-P-salt;

- a cobalt (II) solution was introduced into the graduated tube;

- NaOH was added to pH 5-9 and water to a total volume of 10 ml;

- 0.1 g of sorbent was added and mixed vigorously;

- the sorbent was separated from the solution by decantation, dried in air;

- measured the coefficient of diffuse reflection at 510 nm;

- found the cobalt content according to the calibration graph.

The technical result is to reduce the detection limit, expanding the range of detectable contents.

The specified technical result is achieved by the fact that in the method for determining cobalt (II), which includes preparing a solution of cobalt (II), extracting cobalt (II) from the solution with sorbent-silica, modified polyhexamethylene guanidine, converting it into a complex compound on the surface of the sorbent, separating the sorbent from the solution , the assessment of the color intensity of the surface cobalt complex by the measured diffuse reflection coefficient and the determination of the cobalt content by the calibration graph, the new is that in Silica, sequentially modified with polyhexamethylene guanidine and nitroso-H salt, is used as the sorbent, and the diffuse reflectance is measured at 540 nm.

Signs that distinguish the claimed technical solution from the prototype are not identified in other technical solutions when studying data and related areas of technology and, therefore, provide the claimed solution with the criteria of "novelty" and "inventive step".

The essence of the method lies in the fact that cobalt (II) which is in solution in the pH range of 5-8 is quantitatively (the degree of recovery is 99%) is extracted with silica sequentially modified polyhexamethylene guanidine and nitroso-H-salt.

Sorption of cobalt (II) in the static mode proceeds quickly - the time to establish sorption equilibrium does not exceed 5 minutes. In the process of complexation of cobalt (II) with a nitroso-H salt, a red-colored complex is formed on the surface of the sorbent, which has a maximum in the absorption spectrum at 540 nm.

To 10 g of silica was added 100 ml of a 5% solution of polyhexamethylene guanidine in water, stirred for 5 minutes, the silica was separated from the solution by decantation and washed with distilled water. Then, silica treated with polyhexamethylene guanidine is treated with a 3 × 10 ^-6 M solution of nitroso-H-salt in water, stirred vigorously for 5 minutes, the sorbent is separated from the solution by decantation, washed with distilled water, and dried in air.

Sorbent-silica modified with polyhexamethylene guanidine and nitroso-H salt is added to the test solution with a pH of 5–8 containing cobalt (II), intensively mixed for 5 min, the sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and the diffuse coefficient is measured reflection at 540 nm. The cobalt content is found according to the calibration graph built in the conditions of determination. The detection limit is 0.01 μg cobalt per 0.1 g of sorbent. This amount of cobalt is the minimum concentration that can be recorded on this sample of sorbent on existing devices relative to the background signal, regardless of the method of concentration of cobalt (static or dynamic sorption mode). The use of a dynamic sorption regime allows one to concentrate cobalt from large volumes of solutions. So when sorption of cobalt from 10 ml of the solution, the relative detection limit of cobalt is 1 · 10 ^-3 μg / ml, and when sorption from 1 liter of solution is 1 · 10 ^-5 μg / ml, or 1 · 10 ^-2 μg / l, which almost 5 times less than the detection limit achieved by the prototype method. Thus, the minimum cobalt content, determined by the proposed method, in an arbitrary volume of the solution should be at least 0.01 μg.

The linearity of the calibration graph is maintained up to 5 μg per 0.1 g of sorbent.

Example 1 (prototype). Sorbent silica, sequentially modified with polyhexamethylene guanidine and nitroso-P salt, is added to 10 ml of a solution with a pH of 5–9 containing 0.5 μg of cobalt, stirred vigorously for 5 min, the sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and measure the coefficient of diffuse reflection at 510 nm. The amount of cobalt is found according to the calibration graph built in similar conditions. Found 0.47 ± 0.05 μg.

Example 2 (the proposed method). Sorbent silica, sequentially modified with polyhexamethylene guanidine and nitroso-H salt, is added to 10 ml of a solution with a pH of 5-8 containing 0.1 μg of cobalt, stirred vigorously for 5 min, the sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and measure the coefficient of diffuse reflection at 540 nm. The amount of cobalt is found by the calibration graph. Found 0.11 ± 0.03 μg.

Example 3 (the proposed method). Sorbent silica, sequentially modified with polyhexamethylene guanidine and nitroso-H salt, is added to 10 ml of a solution with a pH of 5–8 containing 4.0 μg of cobalt, stirred vigorously for 5 min, the sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and measure the coefficient of diffuse reflection at 540 nm. The amount of cobalt is found by the calibration graph. Found 3.96 ± 0.05 μg.

Example 4 (the proposed method). 500 ml of an aqueous solution with a pH of 5-8 containing 1 μg of cobalt is passed through a chromatographic column containing 0.1 g of sorbent at a rate of 5 ml / min. The sorbent is removed, placed in a fluoroplastic cuvette and the diffuse reflection coefficient is measured at 540 nm. The amount of cobalt is found by the calibration graph. Found 0.95 ± 0.05 mcg.

The method is characterized by high sensitivity, ease of implementation and does not require the use of expensive equipment, harmful substances and inaccessible sorbents - chemically modified silica gels. The use of sorbent, silica, sequentially modified with polyhexamethylene guanidine and nitroso-H-salt, allows to reduce the detection limit of cobalt by 5 times compared to the prototype method and to expand the range of determined contents.

The increase in the color intensity of the sorbent with increasing concentration of cobalt on its surface allows the use of this sorbent as a test tool for rapid test determination of cobalt.

Claims (1)

A method for determining cobalt (II), including the preparation of a cobalt (II) solution, extracting cobalt (II) from a solution with sorbent-silica, modified polyhexamethylene guanidine, converting it into a complex compound on the surface of the sorbent, separating the sorbent from the solution, estimating the intensity of coloring of the surface complex of cobalt by measured diffuse reflection coefficient and determination of cobalt content according to the calibration graph, characterized in that silica is used as a sorbent, sequentially modified and polyhexamethyleneguanidine nitroso-N-salt, and the diffuse reflectance was measured at 540 nm.