RU2457481C1 - Method of detecting cadmium (ii) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves preparation of a sorbent, cadmium (II) solution, extraction of cadmium (II) from the solution using the sorbent and conversion thereof to a complex compound on the surface of the sorbent, separation of the sorbent from the solution, measurement of luminescence intensity of the cadmium (II) surface complex and determination of cadmium content from a calibration curve. The sorbent used is silica gel which is successively modified with polyhexamethylene guanidine and 8-oxyquinoline-5-sulphonic acid, and luminescence intensity is recorded at 478 nm.

EFFECT: high sensitivity, simpler and faster analysis.

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Description

The invention relates to analytical chemistry of elements, in particular to methods for the determination of cadmium (II), and can be used in its determination in natural and man-made waters.

Various methods of analysis are used to determine cadmium, in particular, molecular spectroscopic (spectrophotometry and luminescence), which are characterized by high sensitivity and selectivity, ease of determination and do not require expensive equipment.

To reduce the detection limits and increase the selectivity of the determination of elements, a combination of preliminary sorption preconcentration with subsequent determination of elements directly in the sorbent phase is widely used.

For the sorption-molecular-spectroscopic determination of cadmium (II), it is necessary to fulfill the conditions for the formation of cadmium (II) complexes on the surface with functional groups of the sorbent that have their own color or luminescence, the intensity of which varies in proportion to the cadmium (II) content on the surface of the sorbent.

A known method of sorption-photometric determination of cadmium (II) [RF Patent No. 2361660 The method of concentration and determination of copper, lead and cadmium / Tataev SD, Byurnaev UG, Gasanova ZG]. The method is based on the sorption isolation of cadmium (II) by the sorbent Amberlit JRA-400 with a fixed complexing organic reagent - zinc. The sorbent quantitatively extracts cadmium (II) from solutions within 10 minutes, while a color develops, the intensity of which is proportional to the cadmium (II) content in the analyzed solution.

The method involves the following operations:

- the analyzed water is filtered off from mechanical impurities, add 6 ml of 50% H ₂ SO ₄ , boil for 10-15 minutes and settle for 1 hour;

- excess acid is neutralized with 10% ammonia to a pH of 2.0 to 2.5;

- 0.2 g of sorbent is added to the sample, 0.1 M NaOH or 0.1 M HCl is added to create a pH of 4.5-5.0, stirred vigorously for 10 minutes;

- the sorbent is separated from the solution, washed with distilled water, dried to an air-dry state and the color intensity of the sorbent (diffuse reflection coefficient) is measured at a wavelength of 570 nm;

- the calculation of the content of cadmium (II) is carried out according to the calibration schedule.

The disadvantages of this method include low sensitivity, a long duration of determination.

Closest to the proposed method in technical essence and the achieved results is a sorption-luminescent determination of cadmium (II) using a solid sorbent with non-covalently fixed 8-hydroxyquinoline-5-sulfonic acid [Zhang Zhujun, W. Rudolf Seitz A fluorescent sensor for aluminum (III ), magnesium (II), zinc (II) and cadmium (II) based on eletrostatically immopbilized quinolin-8-ol sulfonate // Analytica Chimica Acta. - 1985. - V.171. - P.251-258]. The method is based on the formation of a cadmium (II) compound luminescent at room temperature with a complexing reagent - 8-hydroxyquinoline-5-sulfonic acid, non-covalently attached to a solid support.

The method involves the following operations:

- 2 g of the Amberlite CG-400 ion exchange resin are intensively mixed with 100 ml of a 0.01 M solution of 8-hydroxyquinoline-5-sulfonic acid in water for 12 hours;

- then the resulting sorbent is filtered off, washed with deionized water, dried at 50 ° C and ground in an agate mortar;

- to a sorbent placed on a cellophane film, a solution containing cadmium (II) is supplied at pH 6;

- the sorbent is irradiated with UV light, and the luminescence intensity is measured at a wavelength of 448 nm;

- the content of cadmium (II) is found according to the calibration schedule built in the same conditions.

The disadvantages of the method include a high detection limit (56 μg / l), the need to grind the sorbent before use, the duration of the sorbent.

The technical result of the proposed method is to reduce the detection limit of cadmium (II), simplifying the methodology for determining and reducing the duration of the analysis.

The specified technical result is achieved by the fact that in the method for determining cadmium (II), which includes preparing the sorbent, cadmium (II) solution, extracting cadmium (II) from the solution by the sorbent and converting it into a complex compound on the surface of the sorbent, separating the sorbent from the solution, measuring the intensity the luminescence of the surface complex of cadmium (II) and the determination of cadmium content according to the calibration graph, it is new that silica gel, a series of modified polyhexamethyleneengine, is used as a sorbent idine and 8-hydroxyquinoline-5-sulfonic acid, and the luminescence intensity is recorded at 478 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 proposed method lies in the fact that in a solution of cadmium (II) at pH 5-6 quantitatively (the recovery is ≥ 99%) is extracted with silica gel, sequentially modified polyhexamethylene guanidine and 8-hydroxyquinoline-5-sulfonic acid with a time to establish sorption equilibrium, not exceeding 10 minutes. In the process of sorption, complex compounds of cadmium (II) with 8-hydroxyquinoline-5-sulfonic acid are formed on the surface of the sorbent, which intensively luminesce at room temperature when they are irradiated with ultraviolet light.

To obtain a sorbent, Silochrome S-80 brand silica gel is treated sequentially for 5-10 minutes with a 1% aqueous solution of polyhexamethylene guanidine hydrochloride (PHMG) and an 8.8-10 ^-5 M aqueous solution of 8-hydroxyquinoline-5-sulfonic acid. The sorbent is separated by decantation, washed with distilled water and used for sorption concentration and subsequent determination of cadmium (II). The method of obtaining the sorbent eliminates the use of toxic organic solvents.

The proposed method is as follows:

- the analyzed solution with a volume of 10 ml containing 0.05-1.0 μg / ml cadmium (II), with a pH of 5-6, is placed in a test tube with a ground stopper, 0.1 g of sorbent is introduced and intensively mixed for 10 minutes;

- the sorbent is separated from the solution by decantation, placed in a cuvette and the luminescence intensity is measured at 478 nm. The cadmium content is determined by the calibration curve.

Increasing or decreasing the pH of the solution leads to a decrease in the degree of extraction of cadmium (II) and, as a consequence, to an increase in the detection limit (table 1). A decrease or increase in the concentration of 8-hydroxyquinoline-5-sulfonic acid also leads to a decrease in the detection limit (table 2).

Sorption in the static mode proceeds quickly (5-10 minutes) and quantitatively (the degree of extraction is ≥ 99%), which makes it possible to concentrate and completely recover cadmium (II) even from very dilute solutions in the dynamic mode. The detection limit of cadmium (II) with a weighed sorbent of 0.1 g is 0.2 μg, which is almost 3 times lower than the detection limit of the prototype. The relative detection limit of cadmium (II) when using 10 ml of the solution is 0.02 μg / ml. The calibration graph is linear in the range of 0.5-10 μg cadmium (II) per 0.1 g of sorbent.

In the proposed method, the cadmium (II) content in an arbitrary volume of the solution should be at least 0.2 μg. This amount of cadmium (II) per 0.1 g of sorbent is the minimum concentration that can be fixed on existing devices relative to the background signal. When using 100 ml and the relative detection limit is reduced to 0.002 μg / ml.

Example 1 (prototype). Hydrochloric acid and sodium hydroxide are added to a solution containing cadmium (II) to pH 6, the resulting solution is fed to a layer of solid sorbent to form luminescent complexes, and the luminescence intensity is measured at a wavelength of λ = 448 nm. The cadmium (II) content in the analyzed solution is found according to the calibration curve.

Example 2 (the proposed method). To 10 ml of a solution with a pH of 5-6 containing 0.05 μg / ml of cadmium (II), 0.1 g of a solid sorbent - silica gel with an immobilized reagent 8-hydroxyquinoline-5-sulfonic acid is added, intensively mixed for 10 minutes, the sorbent separated from the solution by decantation, transferred to a cuvette and measured the luminescence intensity at 478 nm. The amount of cadmium (II) is found by the calibration curve. Found 0.052 ± 0.002 μg.

Example 3 (the proposed method). To 10 ml of a solution with a pH of 5-6, containing 0.15 μg / ml of cadmium (II), 0.1 g of sorbent - silica gel with the immobilized reagent 8-hydroxyquinoline-5-sulfonic acid is added, intensively mixed for 10 minutes, the sorbent is separated from the solution by decantation, transferred to a cuvette and measure the luminescence intensity at 478 nm. The amount of cadmium is found by the calibration curve. Found 0.14 ± 0.03 μg / ml.

Example 4 (the proposed method). 500 ml of a solution containing 8 μg / L of cadmium (II) is passed through a quartz capillary filled with 0.1 g of sorbent at a rate of 1 ml / min. The sorbent is removed from the capillary, transferred to a cuvette and the luminescence intensity is measured at 478 nm. The cadmium (II) content is found according to the calibration schedule. Found 8.1 ± 0.6 μg / L.

The method is characterized by high sensitivity, ease of operation, does not require the use of substances harmful to human health. The use of silica gel, sequentially modified with polyhexamethylene guanidine and 8-hydroxyquinoline-5-sulfonic acid, can reduce the analysis time and practically. 3 times lower the detection limit of cadmium (II).

Table 1 The effect of the pH of the solution on the detection limit of cadmium (II) Terms of Definition pH Cadmium (II) detection limit, μg / 0.1 g of sorbent 3 four 5 6 7 8 3.0 0.819 0.2 0.2 0.43 0.5

table 2 The effect of the concentration of 8-hydroxyquinoline-5-sulfonic acid on the value of the detection limit of cadmium (II) Terms of Definition Concentration of 8-hydroxyquinoline-5-sulfonic acid, 10 ^-5 M Cadmium (II) detection limit, μg / 0.1 g of sorbent 0.4 0.9 4,5 9 fifteen 45 0.91 0.47 0.2 0.2 0.45 0.88

Claims (1)

A method for determining cadmium (II), including the preparation of a sorbent, a cadmium (II) solution, extraction of cadmium (II) from a solution with a sorbent and its conversion to a complex compound on the surface of the sorbent, separation of the sorbent from the solution, measurement of the luminescence intensity of the surface complex of cadmium (II), and determination of cadmium content according to a calibration graph, characterized in that silica gel, sequentially modified with polyhexamethylene guanidine and 8-hydroxyquinoline-5-sulfonic acid, is used as the sorbent, and the intensity luminescence is recorded at 478 nm.