SU1562830A1 - Method of determining lead in grape juices - Google Patents

Abstract

The invention relates to analytical chemistry, in particular to the polygraphic method for determining lead in extracts, and can be used in the analysis of grape juices. The purpose of the invention is to increase the express determination and simplify the analysis in the presence of copper, iron, zinc and tin. The objective is achieved in that the interfering metals are separated by extraction in the form of rhodanide complexes into n-butanol. Lead is concentrated from the aqueous phase with 8-hydroxyquinoline in n-butanol. The extraction is polished on a background containing 0.7-1.0 M LICL and 1.0-1.5 M HCL in an ethanolic aqueous solution at a ratio of 1: 4. The lead concentration is determined by the peak height in the potential range from -0.45 to -0.52 V. The analysis time is 20 minutes. 3 tab.

Description

The invention relates to analytical chemistry, in particular to a polarographic method for the determination of lead in extracts, and can be used in the analysis of grape juices.

The purpose of the invention is to increase the expression rate and simplify the analysis in the presence of copper, iron, zinc and tin.

The method is based on the extraction separation of interfering components and the concentration of lead, followed by the polarographic registration of electroactive lead oxyquinolate directly in the extract, namely the selective extraction separation of copper, iron, zinc and tin with a solution of 20%

NH.NCs in n-butanol at pH 1-1.5, concentration of lead by extraction from the aqueous phase at pH 10-12 with 8-hydroxyquinoline to n-butanol, direct polarography of the extract containing lead, against the background (0.7-1, 0) M LiCl + (1.0-1.5) M HC1 in a solution containing ethanol and water in a 1: 4 ratio.

The magnitude of the recovery current and the peak potential of lead depend on the composition of the background components.

The effect of the constituents of the background on the polarographic characteristics of lead 8-hydroxyquinoline in the Pb extract is presented in Table. one .

The use of a polar background (0.7-1.0) M LiCl + (1-1.5) M HC1 in a mixed solvent of ethanol with water in a ratio of 1: 4 ensures the homogeneity of the polarized mixture and makes it possible to record the amount of lead reduction current in potential areas (-0.45) - (- 0.52) B (relative ne) with a sensitivity sufficient to detect lead when it is contained in the sample below the MPC (MPC of 0.2 mg / l). The sensitivity of the determination according to the proposed method is M, which corresponds to 0.002 mg / l.

Example. 1. Determination of lead in model solutions. 0.5 ml of a model solution containing lead in the amount of, diluted with water to 20 ml in a separating funnel. 1.5 ml of 1 M HC1 solution was added to create an acidic medium. 1.5 ml of an aqueous solution of 20% and 15 ml of n-butanol are introduced. Allow 1 min. The organic phase was discarded. The aqueous phase was washed twice with 15 ml of n-butanol and poured into a measuring tube with a 25 ml section. The butanol product was washed with 4 ml of 0.1 M HC1 and the aqueous phase was poured into the same tube.

I

Added to the solution of 2.2 ml of 10 M

KOH (osch.) And introduced 4 ml of a 0.05 M solution of 8-hydroxyquinoline in n-butanol. Extracted for 1 min. After settling, 2 ml of the solution was taken from the organic layer and diluted in a volumetric flask with 10 ml of a polarographic background — 0.85 M LiCl f 1.0 M HC1 in a saline water (1: 4). The solution was transferred to a polarographic cell (three-electrode) and oxygen was removed from the solution for 20 m. The lead current polarogram was recorded on a PU-1 polarograph in the range of (-0.45) - (- 0.52) ( Rel. n.c.e.) in the following mode: Y 2 mV / s, A 10 mV, CfHa4 -0.2 V tCMHX 2 s; Mx 100 mV / cm, My 10 mV / cm. Tast mode with a rectangular shape of polarizing voltage. In tab. 2 shows the data on the determination of lead in model solutions with different contents of interfering elements, carried out through all stages of the analysis. The lead content is found on a calibration graph, constructed from model solutions with known content.

Example 2. Determination of lead

in samples of grape juice.

-10 ml of water and 1.5 ml of 1 M HC1 were added to 10 ml of grape juice. Extracted and recorded by poro- | gram of lead hydroxyquinoline extract

3 in the same way as in Example 1. The lead content was found according to a calibration graph constructed using standard solutions of natural grape juice, which does not contain lead, in which additives of a known amount of lead were added. Natural grape juice for a children's guitar of the Tiraspol Experimental Plant served as such a standard sample.

5 In table. 3 shows the results of the determination of lead in various samples of grape juice.

Preparation of one sample for determination is no more than 20 minutes and gives a gain in time by 15–20 times.

Claims (1)

Invention Formula A method for determining lead in grape juices, which includes an extraction department followed by a polarographic definition, characterized in that, in order to increase the rapidity of determination and simplification of the analysis in the presence of copper, iron, zinc and tin, the interfering metals are separated by extraction from viraneanides in n- butanol, then the lead is concentrated from the aqueous phase with 8-hydroxyquinoline dissolved in n-butanol, followed by polygraphy of the extract on a background containing (0.7-1.0) M lithium chloride and (1-1.5) M salt hydrochloric acid in this one the bottom solution at a ratio of 1: 4, and the lead concentration was determined by peak height in the potential range (-0.45) - (0.52) B. Table 1 0.01 0.0076 - 0.015 - 0.41 - 0.75 Table 3 0,002 0.27 0,0074 ± 0,005 0,00060,0390,015 ± 0,002 0.0580.1410.41 + 0.09 0.0420.0570.75 + 0.08