SU1682866A1 - Method for copper determination in water - Google Patents

Abstract

The invention relates to methods for determining copper in water by sorption concentration, elution with a solution of an organic reagent and subsequent photometric measurement. The goal is to increase the sensitivity of the analysis. The proposed method for the determination of copper consists in the sorption of copper (II) ions on silica, containing grafted iminodiacetic groups on the surface in an amount of 0.29-0.525 groups / nm2. and subsequent elution of copper with a solution of thioketone Michler in the presence of 0.015-0.15 M sodium dodecyl sulfate. The presence of chelating iminodiacetic groups on the surface of silica allows for the quantitative sorption of copper ions at a sufficiently low content in solutions. The proposed method allows to increase the sensitivity by a factor of 20 to 0.1 µg / l, as well as the selectivity of the analysis. Almost only platinum interferes. 1 zp. F-ly, 1 ill., 6 tab. J

Description

The invention relates to methods for determining copper, based on sorption concentration, the formation of a colored compound with an organic reagent, and can be used to determine copper in drinking and surface waters, as well as in deposited water.

The aim of the invention is to increase the sensitivity of the analysis

The drawing shows graphs explaining the proposed method.

To achieve this goal, a method for determining copper in waters is proposed. It consists in concentrating copper ions on silica containing grafted iminodiacetic groups in the amount of 0.29-0.525 groups / nm2, treating the sorbent with copper with a solution of thioketone Michler sodium dodecyl sulfate (SDS) at pH 5-7, followed by recording the optical density of the colored solution.

The formation of a colored compound of copper with thioketone occurs in the presence of ascorbic acid, which is necessary for the reduction of copper (II) to copper (I). Copper (II) does not form a colored compound with a reagent. Under these conditions, only platinum (IV) interferes with the determination of copper with Michler's thioketone.

The sensitivity and selectivity of the Michler thioketone used as eluent is high when the colored copper complex with the reagent is formed in sodium dodecyl sulfate. The introduction of an anionic surfactant into the system leads to an increase in the detection limit of the photometric reaction. In addition, the introduction of surfactants into the system helps to increase the strength of the complex and the interfering influence of many complexing agents.

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(hydroxy acids, including humic acids, halide - ions, thiourea) manifests itself at concentrations much higher than in organic solvents. Thus, for example, an oxalate ion has a significant effect (determination error of 10%) on the determination of copper with Michler's thioketone in a water-dimethylformamide medium at a concentration of 5 mg / l, and in a DSA medium only at a concentration of 1 g / l.

The effective effect of DDS is manifested only when using Michler's thioketone (Table 1).

The proposed parameters for the determination of copper (the number of iminodiacetic groups on the surface of silica, the concentration of sodium dodecyl sulfate, the pH of the medium) are selected from the conditions that provide high sensitivity with high accuracy (Table 2, Examples 1-11). As can be seen from Table 2 (Examples 1- 3), the optimal number of iminodiacetic groups on the silica surface is 0.29-0.52 groups / nm. Fixing a larger number of complexing groups on the surface is a difficult task, and the presence of a smaller number of these groups leads to izheniyu exactly determine and to improve the detection limit (Table 2, Examples 12 and 13). The optimal concentration of dodecyl sulfate nef 1 i in the solution of the eluate is 0.015-0.15 M (Tobl.2, Examples 4-8). At the center of the DDS below 0.015 M, the detectable limit of the limit is not reached, Sponsored (tag, examples 14, 15 ), and the concentration of SDS in the solution of more than 0.15 M cannot be created as it is already t, a - the solution is practically saturated at room temperature, the optimum acidity of the eluate solution is 5-7 (Table 2, examples 4-7). When the acidity of the solution is higher and lower than these values, the required SD is not achieved (Table 2, Examples 16-19) and the accuracy of determination is reduced.

The formation of a complex of copper with Micpera's thioxytoxide occurs in the presence of ascorbic acid, which is necessary for the reduction of copper (II) to copper (I). Under such reaction conditions, all metal ions having common pH ranges of determination with TCM (palladium (M), platinum (II), gold (IH), mercury (1, I), silver (I) are reduced to the elemental state and do not interact with the reagent. Platinum (IV) in the presence of ascorbic acid is reduced to platinum (II), which forms a colored complex with TCM. However, equilibrium in such a system is established only after 2 h. Dependence of sensitivity and accuracy of copper on the presence of unauthorized metal ions It claimed in Table 3 below. As can be seen from the data determined

the division of copper in the presence of zinc, cadmium, aluminum, cobalt, iron, lead and silver can be carried out with sufficiently high accuracy by the proposed method, despite the fact that all these elements

are sorbed on the surface of the sorbent, but not desorbed by the proposed eluent.

Studies have shown that the chemical and analytical properties of TCM

can be significantly improved if complexation reactions are carried out in surfactant medium. The greatest effect is achieved when introduced into the DDS system.

If in the medium of water-organic solvents copper (I) interacts in a wide pH range (in a water-dimethylformamide medium the optimum pH is 3-10, Table 1), then in the DDS medium the pH range is significantly narrower. optimal pH range is 5-7. The time stability of solutions of a copper (I) complex with a TCM in DDS medium is much higher than that of water – organic solvents. If in the first case the optical density of the colored solutions does not change within 1 hour, in the second case it does not change for only 10-15 minutes.

In surfactant micellar solutions, copper (I) and Michler's thioketone react in a molar ratio of 1: 4. In the same ratio

copper (l) interacts with TKM during extraction with higher alcohols and a mixed solvent of chloroform-butanol (Table 1), in contrast to aqueous-organic media, where the ratio of copper (I): TKM is 1: 2. So

In other words, in the MDD solution, the maximum possible coordination for copper (I) is 4, which is due to the effect of surfactant micelles on the state of the metal ion in the solution, which is quite isolated from the MDS environment, which excludes the possibility of coordinating them with water or solvent molecules.

An increase in the number of coordinated

molecules of the reagent in the composition of the copper (I) complex with the TCM in micellar solutions of DCS leads to an increase in the molar absorption coefficient of the complex, and consequently, to an increase in the sensitivity of the photometric reaction. The introduction of DDS into the system also leads to an increase in reaction contrast. If in a water-dimethylformamide medium the LN is 35 nm, then in the presence of DDS it is 90 nm (DD is the difference between the maximum absorption of the complex and the reagent). The large value of LN (60 nm) is a very valuable property of the photometer. reagent. High contrast enhances the accuracy of instrumental measurements.

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In addition, the introduction of SDS into the copper (I) - TKM system contributes to the increase in the strength of the complex and the interfering influence of many complexing agents (hydroxy acids, including humic acids, halide ions, thiourea) at concentrations of significantly higher than in the environment of organic solvents. Thus, oksatat-ion has a noticeable effect on the determination of copper with TCM in water-dimethyl (i) formamide medium at a concentration of 5 mg / l, and in DDS medium only at a concentration of 1 g / l.

Studies have shown that the introduction of cationic surfactants (cetylpyridinium chloride, decylpyridinium chloride, etc.) into the copper (I) - TKM system does not affect the optical density of the solutions. The introduction of non-ionic surfactants (OP-7, DS-10, etc.) has a slight effect, and the introduction of anionic surfactants (volgonate) has a stronger effect. The greatest effect is achieved with the introduction of sodium dodecyl sulfate (see drawing).

PRI me R 1. 200 ml of bidistilled water with different copper contents (injected) is passed at a rate of 0.02 ml / s through a chromatographic column filled with a sorbent. Then a reagent solution is passed through a layer of sorbent with copper at a rate of 0.02 ml / s. The eluate is stirred and the optical density of the solution is measured on a SpecoMO spectrophotometer at I 540 nm in cuvettes with 1–5 cm (see Table 4).

PRI mme R 2. 100 ml of river water is passed at a rate of 0.06 ml / s through a chromatographic column filled with a sorbent. A reagent solution is passed through the layer of sorbent with copper at a rate of 0.02 ml / s. The eluate is stirred and the optical density of the solution is measured on a Specol-10 spectrophotometer at I - 540 nm in cuvettes with cm (see Table 5).

Example 3. 50 ml of tap water is passed, with a cup (; 0.1 ml / s; through a chromate: refractory filled with the sorbent Measure; a sorbent with copper is passed through a plant reagent at a rate of 0.02 ml / s. The eluate is stirred and The optical float of the solution is measured on a Spf.ccMO spectrophotometer at I 540 nm in cuvettes cm. (see g. b).

The data table. 5 and 6 confirm the advantages proposed; - on the method for determining copper in waters according to the prototype. Using the proposed method makes it possible to increase the sensitivity of the determination of copper in water, which is characterized by a decrease in the detection limit by 500 times from 50 to 0.1 µg / l. In addition, the high sensitivity of copper determination by the proposed method is combined with high selectivity (Table 3).

The proposed method allows the sensitivity of copper detection to be increased by a factor of 20 from 2 to 0.1 µg / L.

The high sensitivity and selectivity of the determination of copper by the presumed method will allow it to be widely and effectively used to control the copper content in waters of various types.

Claims (2)

1. A method for determining copper in water, comprising concentrating on a sorbent containing iminodiacetate groups, elution with a solution of an organic reagent and quantitative registration by photometry of the resulting solution, characterized in that, in order to increase the sensitivity of the analysis, silica and grafted iminodiacetate groups are used as a sorbent in the amount of 0.29-0.52 groups / mm, and the eluent is a solution of Michler's thioketone in the presence of 0.015-0.155 S solution of sodium dodecyl sulfate. 2. A method according to claim 1, characterized in that ascorbic acid is added to the eluate to a pH of 5-7. Table 1 Table 2 - In the study of the influence of various elements (except silver) on sorbion-photometric determination of copper, standard SOW-3 waters are used, containing copper, zinc, cadmium, aluminum, cobalt, rezezo nkelz and lead, introducing different amounts of it into Vidistilled water. Table 3 The proposed method 4.5 5.1 3.5 Table4 Table Found copper, mcg / l / 1 volume absorption method with preconcentration 4.9 5.0 3.7 l- yes c AC;