SU1702283A1 - Method of determining ion concentration in solutions - Google Patents

Description

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(21) 4748202/25 (22) 10/12/89 (46) 12/30/91. Bul

(71) All-Union Research and Design Institute of Chromatography

(72) O.A.Sagatel, A.V. Kartavtsev and B.M.Kulakov

(53) 543.257.1 (088.8)

(56) Kulakov M.V. Technological measurements and instruments for chemical production. M .: Mashinostroenie, 1974, p. 255-277.

Powley, C.P., Anal. Chem. Acta, 1983, 152, p. 173-190.

(54) METHOD FOR DETERMINING THE CONCENTRATION OF IONS IN SOLUTIONS

(57) The invention relates to methods for determining the concentration of ions in aqueous solutions and can be used in analytical control devices in highly polluted media in order to simplify the measurement method. The goal is achieved by the fact that bipolar voltage pulses with an amplitude of 0.8-2.0 V are applied to the electrode system consisting of an ion-selective electrode with a solid electrolyte membrane, which has a selective electrical conductivity according to the type of ion and an auxiliary inert electrode. each pulse has a duration of 15–20 s, the current being measured at the time of exposure to a voltage pulse, the polarity of which is opposite to the sign of the ion being detected. 1 il.

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The invention relates to methods for determining the concentration of ions in solutions and can be used in analytical control devices in highly polluted media.

The purpose of the invention is to simplify the method of measurement,

The method is implemented using the device shown in the drawing.

The voltage pulses from the power source 1 through a group of contacts 2 of the time relay 3 are fed to an electrode pair consisting of measuring 4 and inert auxiliary 5 electrodes in cell 6 with the analyzed solution 7 and stirrer 8. Current in measuring circuit 4, measured with a microammeter 9, is proportional to the concentration of the detected ions.

When a voltage is applied to the electrode system, the dissociated ions begin to move to oppositely charged electrodes. The polarity of the measuring electrode must be opposite to the sign of the charge of the ion being detected. An electrode with a solid electrolyte membrane 10 is used as the measuring electrode.

Due to the specificity of the crystal lattice of a solid electrolyte, the current through the membrane of the measuring electrode is caused only by the ions of the component being detected. Consequently, the electric current in the circuit of the measuring electrode is proportional to the concentration of the type of ion being determined and is practically independent of the indefinable components of the solution.

In the measurement process, especially in heavily contaminated solutions, not only the detected ions, but also other ions present in the system, move to the electrode system.

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The analyzed solution is ions and contaminated particles.

When this occurs, other types of ions are concentrated at the surface of the measuring electrode, which, due to the specificity of the properties of the solid electrolyte membrane, cannot penetrate deep into it, but accumulate on the surface, forming insoluble compounds and conglomerates. This leads to contamination of the active surface of the electrodes in contact with the sediment layer being analyzed by the solution, partial shielding of the measuring system and, as a result, drift of readings. This deficiency is characteristic of all electrochemical measurement methods (potentiometry, coulometry, conductometry, prototype) when operating in highly contaminated solutions.

To eliminate the drift of indications caused by contamination of the electrode system, achieve self-cleaning of the electrodes, and eliminate the possibility of polarization of the electrodes, in the proposed method, after each half-period of current measurement, a voltage pulse equal to the amplitude and duration but opposite in sign to the measuring . In this case, the electric field repels deposited particles from the surface of the measuring solid electrolyte membrane and the auxiliary electrode. This self-cleaning process of the electrode system allows to increase the reproducibility of readings and increase the interval between maintenance of the system.

Solid electrolyte membranes of 99.2% + 0.8% EuF2 were used to determine the concentrations of fluoride and Ag2S ions to determine the concentrations of sulfide ions.

As an auxiliary electrode, a platinum electrode was used, which, upon application of an external voltage, does not lose its properties due to irreversible electrochemical interaction with the components of the analyzed solution, which is inherent in the chlorine-silver electrode used in the prototype.

Experimental data on the reproducibility of the system measurement data during operation in polluted environments for the cases of determining fluorine and sulfide ions at various power voltages for 30 days are presented in

tab. 1 and 2 respectively. The data are given for measuring the concentration of fluoride mol / dm3 ions and sulfide ions 10 mol / dm. In the case of measurement more

high concentrations of these ions, the reproducibility of the measurement results is significantly improved.

As follows from the table. 1 and 2, the optimum range of supply voltages is 0.8-2.0 V with respect to the reproducibility of measurement results. The same range corresponds to the maximum sensitivity and linearity of the method. When the supply voltage is less than 0.8V

The reproducibility and sensitivity of the method is significantly reduced, due to the comparability of the values of the supply voltage and the potential of the electrical double layer of the measuring electrode. By increasing

power supply voltages higher than 2.0 V may be induced by indefinable types of ions with a charge of the same sign as that determined by a strong electric field in the upper layer of the ionic crystal lattice of the measuring electrode membrane; this leads to a decrease in the reproducibility of the measurement results.

The determination time was determined experimentally and is

15-20 s.

The use of the method makes it possible to simplify the process of determining the concentration of ions, increase the reproducibility of the analysis and increase the interval between maintenance of the system.

Claims (1)

The invention of the method for determining the concentration of ions in solutions, including the measurement an electric current passing through an electrode system consisting of an ion selective electrode with a solid electrolyte membrane having a selective electrical conductivity on the ion to be detected, and an auxiliary electrode when applying external voltage pulses, characterized in that, in order to simplify the method, as an auxiliary electrode use an inert electrode in the analyzed medium, the amplitude of bipolar pulses is 0.8-2.0 V with a pulse duration of 15-20 s, and the current is measured at the moment of impact on the pulse system, the polarity of which is opposite to the sign of the ion being detected. Table 1 table 2