SU1179195A1 - Method of determining concentration of ions in solutions - Google Patents

Abstract

METHOD FOR DETERMINING THE CONCENTRATION OF IONS IN SOLUTIONS, which consists of selectively introducing them into a carrier solution followed by determining its concentration, characterized in that, in order to improve the accuracy of determination, the selective extraction of the analyzed ions into the carrier solution is carried out by electrodialysis, while the concentration of the analyzed The ions in the carrier solution are kept constant by adjusting the voltage on the electrodialysis cell electrodes, and the ion concentration is determined by the voltage of the cell current.

Description

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Srig, 1 The invention relates to electrochemistry, is intended for the continuous measurement of low concentrations of components in weak, highly concentrated solutions and can be used, for example, in the production of caustic soda by the membrane method for the continuous determination of the content of sodium chloride NaCl in it. A known electrochemical method is used to automatically determine the content of ions, for example chlorine ions, in an aqueous solution, according to which a water-soluble iodide is added to the analyzed solution to form its concentration stoichiometrically equivalent to the amount of chlorine to be determined. The resulting solution is fed to an electrolytic cell operating on the principle of cathode depolarization. The measure of chlorine concentration in the analyzed solution is the value of the current passing through the cell. The disadvantages of this method are the introduction of a reagent (iodide) directly into the analyzed solution, a long analysis time and inapplicability for concentrated solutions, I The closest in technical essence to the proposed The method of determining the concentration of ions in solutions, which consists in selectively separating them into a carrier solution and then determining its concentration in it. The disadvantage of this method is However, the accuracy of the determination is low, due to the following factors: exact sample dosing is required; the transport of analyzable ions by dialysis follows the Fick law (this leads to the fact that with decreasing concentration differences, the ion flux decreases and at some small value of the concentration difference the ion flux will be less than the detection limit in the carrier solution). This factor leads to a complete loss of instrument sensitivity. In addition, the device has a non-linearity of static characteristics in a wide range of changes in the analyzed component. The purpose of the invention is to increase the accuracy of determination. The goal is achieved by the method of determining the concentration of ions in solutions, which consists in selectively separating them into the carrier solution and then determining concentration, selective separation of the analyzed ions in the carrier solution is carried out by electrodialysis, while the concentration of the analyzed ions in solution the separator is kept constant by adjusting the voltage on the electrodialysis cell electrodes, and the ion concentration is determined by the cell current. When an electric field (electrodialysis) is applied to dialysis. the ion flux increases due to the migration component, which can be regulated by the voltage on the electrodialysis electrodes and, consequently, to improve the measurement accuracy at low concentrations of the analyzed ions. In addition, maintaining the concentration of ions in the carrier solution constant allows the static characteristic to be correlated and, consequently, to increase the measurement accuracy over a wide range of changes in the concentration of the analyzed component. Fig. 1 shows the scheme of the method implementation; FIG. 2 shows the experimental dependence of the electrodialysis current on the concentration of chlorine ions in the solution being analyzed. The circuit consists of an electrodialysis cell 1, which is divided into two chambers by an ion-exchange membrane 2. The cathode chamber is connected by a supply line 3 and a line 4 to the process flow pipe 5. Discharge carrier 6 is fed into the working chamber of the electrodialysis cell. The working chamber of the electrodialysis cell C is connected by a dispenser 6; a measuring cell 9 in which the indicator electrodes 10 are placed, the emf of which is supplied. to the input of the converter EMF of the indicator electrodes into a unified signal, which is supplied to the comparison element M, also connected with the setpoint generator, the required potential value 12, the Output3 signal of the comparison element is controlled with an adjustable current source 13, which allows to regulate the voltage on the generator electrodes 14 electrodialysis cells. The indicator 15 current electrodialysis cell is included in the same circuit. Example. Measurement of sodium chloride concentration in caustic. The analyzed solution, which is a combination of components of NaOH + NaCl + H2 0 with concentrations of NaOH of 20–40%; NaCl O t 0.1%; H, 0 the rest, is fed into the cathode chamber of the electrodialysis cell 1, from where the C and OH ions are transported by the electrodialysis current through the ion-exchange membrane 2 to the carrier solution stream 7, for example, a dilute sodium nitrate solution of NaNOa is used. The carrier 7 containing the test ions is passed through the cell 9 with the measuring electrodes 10. The EMF E generated on these electrodes will be functionally related to the concentration of the test C1 ions in the dissolver. This EMF is used as a control signal, in accordance with which the electrodialysis current 1 is changed (its value is constantly changed in such a way that the EMF E on the electrodes remains at the specified value E). Thus, the current of electrodialysis I at any time will be a measure of the concentration of chlorine ions in the carrier solution, i.e. ultimately a measure of the concentration of sodium chloride in the analyzed solution. 54 The table presents the results obtained by experimentally determining the dependence of the current strength in electrodialysis one, ke on the concentration of sodium chloride in the caustic. 1.46 / 200 2.92 / 200 The equivalent sodium chloride concentration in caustic was determined as the ratio of the NaCl concentration (g-equiv./l) to the NaOH concentration (g-equiv./l), the potential of the electrode system was kept constant and equal to 290 mV. The constructed characteristic (Fig. 2) confirms the linear nature of the dependence (4) and the high sensitivity of the method, which is 120 mA /% of concentration. The proposed method allows the concentration of the analyzed ions in the carrier solution to be kept constant and at the level of the maximum sensitivity of the analyzer. At the same time, the analyzer as a whole, implementing the proposed method, has a linear static characteristic with maximum sensitivity.

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Claims (1)

METHOD FOR DETERMINING ION CONCENTRATION IN SOLUTIONS, which consists in selectively introducing them into the carrier solution with subsequent determination of the concentration in it, characterized in that, in order to increase the accuracy of determination, the selective analysis of the analyzed ions in the carrier solution is carried out by electrodialysis, while the concentration The analyzed ions in the carrier solution are kept constant by controlling the voltage at the electrodes of the electrodialysis cell, and the ion concentration is determined by the value of the cell current. c <o ω FIG. 1 1 1179195