SU1622812A1 - Composition of membrane of ion-selective electrode for determining chloride-ions - Google Patents

Description

one

(21) 4662067/25

(22) 01/10/89

(46) 01.23.91. Bup. And 3

(71) Leningrad State University

(72) Lohn „Moskvin, D.V.Golikov and S.N. Khromov-Borisov

(53) 543.257 (088.8)

(56) Marshall G.B. Analyst, 1978,

v, 103, p. 438.

U.S. Patent No. 3,563,874, Cl. G 01 N 27/333, 1979, (54) COMPOSITION OF THE MEMBRANE OF IONOSELECTIVE ELECTRODE FOR DETERMINATION OF CHLORIDE-IONS

(57) The invention relates to physicochemical methods of analysis. The purpose of the invention is to expand the range of detectable concentrations by increasing the range of linearity of the chloride function in the microconcentration region. Gl of this in the composition of the membrane containing chloride and silver sulfide, silver sulfate is additionally introduced in the following ratio of components, wt.%: Silver sulfate 4-6; silver chloride 20-76; silver sulphide - the rest. 2 ill., 1 tab.

This invention relates to physicochemical methods of analysis and may find application in chemical technology and hydrochemistry.

The aim of the invention is to expand the range of linearity of the chloride function of the ion-selective electrode in the region of low concentrations.

FIG. Figure 1 shows the range of optimal formulations for making membranes of ion selective electrodes; in fig. 2 is a graph of the EMF of the electrochemical cell versus the logarithm of the activity of the chloride ions.

This goal is achieved by the fact that silver sulfate is additionally added to the ion-selective electrode membrane for determining chloride ions containing silver chloride and silver sulfide in the following ratio, wt.%:

Silver Sulfate4-6

Silver chloride 20-76

Silver sulphideErest

For electrodes with membranes containing less than 4 wt.% Silver sulfate, it is not possible to achieve an expansion in the range of linearity of the electrode function in the microconcentration region of chloride ions. Electrode characteristics of membranes containing more than 6 wt.% Silver sulfate, poorly reproducible, Electrodes with membranes containing less than 20 wt.% Silver chloride or sulfide, are characterized by poor electroanalytical parameters, in particular, are characterized by low reproducibility of potentials.

Example. For the manufacture of an electrode membrane, the composition 5 76 AgCl-20 Ag2S takes 0.050 g.

silver veil, 0.550 g of silver chloride and 0.400 g of silver sulfide, triturated in an agate mortar and pressed on a hydraulic press under a pressure of 100 MJla. The membrane is a cylinder 8 mm in diameter and 3 mm thick.

The membranes are glued in with an epoxy compound into the end of the polished chloride body of the electrode. Internal rastAl, AgCl KC1 II KNO,

us. | 1 mol / l

Calibration solutions are prepared from 1 mol / l potassium chloride. Solutions with chloride ion concentrations of 1 -10 mol / l are prepared immediately before measurements of the D tefpon cell by adding to 100 ml of 1 10 emol / l of a solution of potassium nitrate prepared in deionized water, corresponding amounts of more concentrated solutions. potassium chloride. To measure the EMF of an electrochemical cell, use a pH meter or an I-130 type digital ionometer,

The calibration of the electrodes is carried out SLD in the following way.

Wash the electrode with distilled water. Electrodes are placed in a standard potassium chloride solution and the cell's EMF is measured after 5 minutes (the time is measured with a stopwatch).

The mean emf and its standard deviation are calculated for five parallel measurements, after which the concentration of the standard solution is increased.

Fig. 2 shows the characteristic dependences of the electromotive force / cell emf on the logarithm of the concentration of chloride ions in the solution for an electrode with a membrane of the proposed composition and a polycrystalline electrode based on a mixture of silver chloride and silver sulfide. It can be seen that the electrodes with membranes containing silver sulfate, with the selected measurement method, have an extended range of linearity of the electrode function as compared with the known

The table shows the main electrode characteristics of the electrodes with membranes of the proposed composition.

the thief has the composition: AgN09 + 0.1 mol / l KNO-. The inner reference electrode is silver to wire.

Before each measurement, the outer surface of the membrane is polished with emery paper (type O) and placed in an electrode in 1-10 mol / l KC1 solution, which is kept for 5 minutes,

The following electrochemical cell is used to measure electrode characteristics:

0

25

-IQ

,,.

before

Q

ion selective electrode

45

test solution

As can be seen from the table, for the proposed electrodes, the lower limit of the linearity range is shifted by the order of the microconcentrations of chloride ions. At the same time, the reproducibility of the potentials of the electrodes in dilute solutions of chloride ions is 1.5-6.0 cV, which allows a direct potentiometric determination in the concentration range of 1 - - 1 10 mol / l with an error of L-24%.

The selectivity coefficients, the working area pH and the response times of the proposed electrodes almost coincide with the known ones, i.e. The incorporation of silver sulfate into the membrane does not affect these parameters.

Thus, the proposed membrane membrane compositions of ion-selective electrodes for the determination of chloride ions provide an extension of the linearity range in the microconcentration region of chloride ions.

Claims (1)

Invention Formula The composition of the membrane of the ion-selective electrode for the determination of chloride ions, including silver chloride and silver sulfide, is characterized in that, in order to expand the range of detectable concentrations by increasing the linearity range of the chloride function in the microconcentration region, silver sulfate is additionally introduced into it at the following the ratio of components, wt.%: Silver sulfate 4-6 Silver chloride 20-76 Silver sulphideErest E, m o 1оо150AaiSO, AgiS FIG. /