SU1187063A1 - Method of differential voltammetry - Google Patents

Abstract

A METHOD FOR DIFFERENTIAL PULSE VOLTAMPEROMETRY, which consists in applying a polarizing voltage to the electrochemical cell, which includes a voltage sweep and a pulsed voltage with a high porosity, and measure the current of the electrochemical cell in a time interval shorter than the pulse duration with a high porosity, and measure the current of the electrochemical cell in a time interval that is shorter than the pulse duration and measure a high duty cycle. in order to increase the sensitivity of determining the concentration of irreversibly reducing substances by using the asymmetry of reactions to pulses of different polarity, pulsed April is given in the form of a sequence (L symmetric and opposite-polarity pulses with a zero time interval between them.

Description

one

The invention relates to a measurement technique, is intended to determine low concentrations of irreversibly reducing substances, and can be used in biology, chemical and other industries.

The aim of the invention is to increase the sensitivity of determining the concentration of irreversibly reducing substances by using the asymmetry of reactions to pulses of different polarities.

FIG. 1 is a timing diagram of a polarizing voltage of an electrochemical cell; FIG. 2 is a timing diagram for the Ichip pulsed component of the current for electrochemical reactions f in FIG. 3 time diagram of the pulse component of capacitive current; in fig. 4 is a timing chart of the measured current of the electrochemical reaction in FIG. 5 - structural. scheme of the device for implementing the method.

An apparatus for carrying out the method comprises a source 1 of a sequence of radiopolar pulses, a source 2 of a voltage sweep, a source 3 of a constant initial bias, a potentiostat 4, a current-measuring resistor 5, an amplifier 6, an electrochemical cell 7, a synchronizer 8, a device 9, time selection, matching cascade 10 and the registrar 11.

The device works as follows.

The synchronizer 8 generates a clock pulse and, with an adjustable delay, Starts the source 1 of a sequence of different-polarity pulses. The source 2 of the voltage sweep produces a sweep voltage, which varies with the adjustable speed in the desired voltage range. The initial voltage source 3 produces a stabilized constant voltage of the required magnitude and polarity. All these voltages through the potentiostat 4 and the current-measuring resistor 5 enter the cell 7 and cause the current to flow in it. The pulse component of this current is amplified by an amplifier 6 and fed to a time selection device 9, the operation

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which is synchronized by pulses generated at source 1. Next, the signal at intervals of time (Fig. 2 and 4) is passed through a time selection device through

matching cascade 10 on the recording device 11, where the recording of the voltammogram.

Example. A polarizing voltage is applied to the polarographic cell, which includes the initial voltage O f (linearly varying sweep voltage and a two-pole pulse voltage.

The pulse duration T (Fig. 1) is 40-200 ms, the interval between pulses i tshg 2-4 s. The amplitude of the pulse half-period E, 4100 mV. The voltage pulse component causes the cell to flow through the cell of the pulse component of the cell current, which contains the pulse components of the electrochemical reaction current and capacitive current (Fig. 2

and 3). In this case, the pulse component of the current of the electrochemical reaction has the form of opposite-polarity pulses, the vertices of which decrease according to the law i. Currents are measured in the interval

time Ai,, btj,,, etc. When the electrochemical reaction is found, the moduli of the signals measured in the intervals it, and at, ut and ui, etc. (Fig. 4), although the time coefficients corresponding to q {;, and the fitgt, etc., are quite close, the greater the difference, the closer the polarization potential approaches the peak potential. This difference is significant for irreversibly reducing depolarizers, in which there is a significant decrease or increase in current peaks during the flow of reverse polarity pulses. As is known, the peak heights of voltammograms of irreversibly reducing substances are approximately an order of magnitude smaller than the peaks of reversibly reducing substances.

However, in the proposed method, when the algebraic sum of two opposite-polarity signals is measured, the signals of reversible and irreversible processes are of the same order.

The current capacity of the double layer under the action of a pulsed voltage, reaching a maximum, decreases rapidly in the order of —k / RC J, gg 1; current time

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R is the ohmic resistance in the circuit of the cell, C is the capacity of the double layer (Fig. 3). The capacity of a double layer in the time interval of a single bipolar pulse is almost unchanged. Therefore, the sum of two capacitance of different polarity, measured in time intervals L and itj Ai, etc .; will be almost zero, even if at the time of the beginning of the measurement of cell current during the half-period

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pulse absolute value of capacitive current will not be zero. The currents caused by the positive and negative half-periods of one double-impulse imparted in the time interval g, and Aij ii, etc., are summed algebraically, the received signal after amplification is recorded as the dependence of the impulse component of the current on the polarization voltage.

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Claims (1)

METHOD FOR DIFFERENTIAL PULSE VOLTAMPEROMETRY, which consists in applying a polarizing voltage to the electrochemical cell, including a voltage scan and a pulse voltage * with a large duty cycle, and measuring the current of the electrochemical cell in a time interval shorter than the pulse duration, characterized in that, for the purpose increasing the sensitivity of determining the concentration of irreversibly reducing substances through the use of asymmetry of reactions to pulses of different polarity, pulse voltage a set of a sequence of symmetric and bipolar pulses with a zero time interval therebetween. Figure 1 ¢ 904811HS