RU2428686C1 - Method of determining cobalt (ii) using polymethacrylate matrix - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: method involves preparation of a cobalt (II) solution, extraction of cobalt (II) using a membrane with immobilised 1-(2-pyridylazo)-2-naphthol, followed by separation thereof from the solution, measuring the analytical signal and calculating content of cobalt (II). The membrane used is a polymethacrylate matrix with immobilised 1-(2-pyridylazo)-2-naphthol and the analytical signal used is light absorption at 620 nm or visual estimation of the colour intensity of the optical membrane. Content of cobalt is calculated using a calibrated curve or a visual test method. ^ EFFECT: high sensitivity and information content of analysis. ^ 4 ex, 3 tbl, 1 dwg

Description

The invention relates to the field of analytical chemistry, and in particular to methods for the determination of cobalt (II), and can be used in its determination in natural and drinking waters, in technological solutions, as well as in pharmaceutical preparations.

A known method for the determination of cobalt (II) on a solid phase by diffuse reflective spectroscopy (US Pat. 2374638, Russia, IPC G01N 31/22. Method for the determination of cobalt (II) / Losev VN, Maznyak NV, Didukh S.L. ., Trofimchuk A.K., No.2008140259 / 04; claimed 2008.10.09; published 2009.11.27). The method is based on the quantitative extraction of cobalt (II) from a solution with a pH of 5-9 silica sequentially modified with polyhexamethylene guanidine and nitroso-P salt. As a result of the complexation of cobalt (II) with a nitroso-P salt, a red-brown complex is formed on the surface of the sorbent. To assess the content of cobalt (II) according to the calibration graph, the diffuse reflection coefficient of the sorbent with the obtained complex compound of cobalt (II) is measured at 510 nm.

The disadvantages of the proposed determination method include the complexity of the equipment used in the method for measuring the diffuse reflection coefficient of the sorbent, because The most commonly used method in analytical laboratories is the molecular spectroscopy method, which is based on measuring light absorption due to its high ability to adapt to a wide range of analytical problems. When developing determination methods using a solid phase based on the measurement of light absorption, various transparent materials are used as carriers for immobilizing the reagents.

A known method for the determination of cobalt in pharmaceutical preparations on a solid phase by solid-state spectrophotometry (LSGTeixeira, ACSCosta, J.C. R. Assis, SLC Ferreira and M. Korn / Solid phase specrophotometry for the determination of cobalt in pharmaceutical preparation // microchimica Acta 2001. V.137, N, P.29-33). The method is based on the separation of cobalt (II) from solutions with pH 7 of C-18 silica with immobilized 1- (2-thiazolylazo) -2-naphthol, followed by separation of the sorbent from the solution and its photometry at λ = 572 nm.

The disadvantages of the proposed method for determining cobalt include the complexity of measuring the light absorption of silica, which leads to the need to use the method of "two wavelengths" to take into account the influence of the intrinsic absorption of the sorbent on the value of the analytical signal.

The closest analogue to the claimed invention is a method for determining cobalt by spectrophotometry using a triacetyl cellulose membrane (S. Rastegarzadeh and Z. Moradpour. Construction of an optical sensor for cobalt determination based on methyltrioctylammonium chloride immobilized on a polymer membrane // Instrumentation Science and Technology. 2007 2007 N.35, P.637-647). The method is based on the sorption separation of cobalt (II) from solutions with a pH of 5 a transparent triacetyl cellulose membrane with immobilized methyl trioctylammonium chloride, the formation of a colored complex of cobalt with a reagent in the solid phase and the measurement of absorption at a wavelength of 627 nm.

The disadvantages of this method include the use in the process of preparation of the membrane to immobilize the reagent of a substance harmful to human health - ethylene diamine, an inconvenient way to store the finished membrane, the low sensitivity of the method and the high detection limit.

An object of the present invention is to provide a sensitive, environmentally friendly method for determining cobalt with a low detection limit and various options for detecting an analytical signal and estimating cobalt content.

The solution to this problem is achieved by the fact that in the method for determining cobalt, including the preparation of a cobalt (II) solution, extraction of cobalt (II) with a membrane with immobilized 1- (2-pyridylazo) -2-naphthol, its subsequent separation from the solution, measurement of the analytical signal and assessment of cobalt (II) content, characterized in that a polymethacrylate matrix with immobilized 1- (2-pyridylazo) -2-naphthol is used as a membrane, light absorption at 620 nm or a visual intensity estimate are used as an analytical signal optical membrane paint, evaluation of the content of cobalt is carried out by the calibration curve or visual test method.

The essence of the proposed method lies in the fact that cobalt (II) in solution with a pH of 4-11 is extracted with a polymethacrylate matrix with immobilized 1- (2-pyridylazo) -2-naphthol to form a green colored complex with a maximum in the absorption spectrum at a wavelength of 620 nm.

The immobilization of 1- (2-pyridylazo) -2-naphthol into a polymethacrylate matrix was carried out by its sorption from a water-ethanol solution in a static mode. For this, the polymethacrylate matrix was mixed in a 2.5 × 10 ^-4 M reagent solution for 3 min, while the matrix was stained in orange. The immobilized reagent has an absorption maximum at 470 nm. A polymethacrylate matrix with immobilized 1- (2-pyridylazo) -2-naphthol was added to the test solution with a pH of 4-11 containing cobalt (II), mixed thoroughly for 5 min, removed, dried with filter paper, and the analytical signal was measured, followed by the establishment of the dependence of the value of the analytical signal on the content of cobalt (II) and its assessment. Analytical characteristics in comparison with the prototype are presented in table 1.

Example 1. Measurement of the absorption of polymethacrylate matrix and determination of cobalt content according to the calibration graph.

A plate of the polymethacrylate matrix with immobilized 1- (2-pyridylazo) -2-naphthol was placed in 50 ml of the analyzed solution with a cobalt content of 0.0025-0.025 mg with a pH of 4-11 (NaOH, pH meter control) and stirred for 5 min , then removed, dried with filter paper and absorbance was measured at 620 nm. The cobalt content was found by the calibration dependence built in similar conditions. The equation of the calibration dependence has the form: A ₆₂₀ = 0.03 + 0.40 · s _Co (r = 0.9988), where c _Co is the concentration of cobalt (II), mg / L. The linearity range of the calibration dependence is 0.05-0.5 mg / L. The detection limit calculated by the 3s criterion is 0.03 mg / L.

Example 2. Visual test determination of cobalt content. For visual test determination of cobalt, color scales were obtained by scanning samples obtained by constructing a calibration dependence. Visual test determination was performed similarly to the procedure described in example 1, with the difference that after contact with cobalt (II) solutions, the absorption of polymethacrylate matrices was not measured, but their color was compared with a color scale (see drawing) and element concentration was determined semi-quantitatively .

Example 3. Determination of cobalt content in a standard sample and drinking water.

Preparation of drinking water for analysis. Sampling of drinking water was carried out in accordance with GOST R 51593-2000. For analysis, an aliquot was taken into a 50 ml volumetric flask and acted as described in Example 1.

Evaluation of metrological characteristics was carried out according to the results of determining cobalt in a standard sample and cobalt additives in a drinking water sample in accordance with the recommendations for metrology RMG 61. The results are shown in table 2. The mean square deviation of the analysis results obtained under repeatability conditions and the systematic error in relative units amounted to no more than 7.8% and 4.8%, respectively. From the presented results it can be seen that the system is characterized by good accuracy and precision under repeatability conditions.

Example 4. The determination of cobalt (II) in the medicinal product "Cyanocobalamin".

Preparation of the drug “Cyanocobalamin” for analysis. 12 ml of a 0.5 mg / ml solution of the drug “Cyanocobalamin” was placed in a porcelain cup, poured 2 ml of concentrated H ₂ SO ₄ and heated to a dry residue, then the cup was cooled, the resulting solution was transferred into a 50 ml volumetric flask and diluted with distilled water to tags. An aliquot of 10 ml was taken from the resulting solution and acted as described in example 1.

The results of the determination of cobalt (II) by the claimed method are presented in table.3. The correctness was controlled by comparing the results of the determination of cobalt in the medicine “Cyanocobalamin” with the proposed method and the photometric method for determining cobalt (II) in solution using the nitroso-R salt reagent [Photometric determination of elements / Marchenko Z. 1971, p.571]. The results obtained indicate the correctness and repeatability of the proposed method for determining cobalt (II).

An advantage of the claimed invention is to reduce the detection limit by 12 times, increase the detection sensitivity by 30 times, various methods of measuring the analytical signal of the polymethacrylate matrix and estimating the cobalt content. In addition, the claimed method for the determination of cobalt does not require the use of toxic solvents and other harmful substances and is safe for human health.

Table 1 Analytical characteristics of the determination of cobalt (II) Way Response time, min The equation of the calibration dependence (c _{Co (II)} - cobalt content, M) The range of determined contents, M Detection limit, M Prototype 7 A ₆₂₇ = 0.0469 + 798.4 · c _{Co (II)} (0,085-1,3) × 10 ^-4 5.9 × 10 ^-6 The claimed invention 5 A ₆₂₀ = 0.0304 + 23447 · c _{Co (II)} (0.85-8.5) × 10 ^-6 5.1 × 10 ^-7

table 2 The results of the determination of cobalt (II) in a standard sample and drinking water (n = 5; P = 0.95) An object Concentration, mg / L Found, mg / l σ _r ,% σ _c ,% σ (Δ),% Standard sample 0.1 (0,098 ± 0,013) 4.2 4.8 6.4 0.3 (0.31 ± 0.03) 3.8 3.9 5.5 Drinking water (outdoor standpipes) Additive, mg / l 0 0 - - - 0.1 (0,098 ± 0,016) 7.8 1.9 8.0 0 0 - - - 0.2 (0.19 ± 0.03) 7.6 2.7 8.0 σ _r ,% is the standard deviation of the analysis results obtained under repeatability conditions;
σ _c ,% is the standard deviation of the unexcluded systematic error;
σ (Δ),% - the standard deviation of the error of the analysis results.

Table 3 Determination of cobalt (II) in the medicine “Cyanocobalamin” (n = 5; P = 0.95) An object Found, mg / l s _r ,% Found, mg / ml (in terms of
Cyanocobalamin) s _r ,% The medicine "Cyanocobalamin" 21.1 ± 2.3 4.4 0.49 ± 0.05 4.4 (injection 0.5 mg / ml) 20.7 ± 1.5 * 2,8 0.48 ± 0.03 * 3.0 * - found by the photometric method using nitroso-R-salt

Claims (1)

A method for determining cobalt (II) using a polymethacrylate matrix, comprising preparing a cobalt (II) solution, extracting cobalt (II) with an immobilized 1- (2-pyridylazo) -2-naphthol membrane, its subsequent separation from the solution, measuring the analytical signal and evaluating cobalt (II) content, characterized in that a polymethacrylate matrix with immobilized 1- (2-pyridylazo) -2-naphthol is used as a membrane, light absorption at 620 nm or a visual assessment of the intensity of approx optical membrane painting, cobalt content assessment is carried out according to the calibration schedule or by the visual test method.

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