SU648896A1 - Q-metric analysis method - Google Patents

Description

one

The invention relates to electrical analysis methods and can be used to determine small amounts of a substance.

There is a method of Kulonometrich analysis using the potential sweep of the working electrode of an electrolytic cell. Determining the number of elements in this method was carried out over the area between the curves of the current-time 1.

The closest to the proposed invention is a coulometric analysis method consisting in a linear sweep of the potential of the element being determined, and the dependence of the electrolysis current on the potential is recorded, and the content of the element being determined is estimated from the maximum current (taking into account the background current) 2.

The disadvantages of this method of anatisa are the dependence of the maximum magnitude of the electrolysis current on the rate of potential change, which leads to an analysis error when the sweep speed changes during the analysis, as well as the need to record the background current to account for it.

The purpose of the invention is to improve accuracy and simplify the analysis.

This is achieved by integrating the electrolysis current in the forward and reverse directions of a linear potential sweep n to determine the content of the element being analyzed from the difference in the cycle of integrals. Integrating the electrolysis current significantly reduces the effect of the instability of the sweep speed on the analysis result, and the use of two potential sweep directions (direct and reverse) in combination with current integration allows one to automatically account for the background current.

The invention is illustrated in the drawing, which shows: the potential of the working electrode as a function of time (direct and inverse potential sweep in the area of the formal potential of the EO of the element to be determined) (a) and the dependence of the electrolysis current on time or, which is the same for linear sweep, from capacity; Cfqj - background current (b).

When conducting coulometric analysis of the proposed method, the solution with the element to be detected is placed in a three-electrode

the electrolytic cell and linearly increase and decrease the potential of the working electrode with a potentiostat.

The change in potential is carried out in the area of the formal potential of the EO of the element being defined (plot and drawing). When the instantaneous potential of the working electrode coincides with the formal potential of the element being detected, the magnitude of the current of the electron reaches the extremum. The kind of extremum (maximum or minimum) depends on the direction of the sweep (plot b of the drawing). The polarity of the background current. ZF, in contrast to the polarity of the electrolysis current of the element being determined, does not depend on the direction of the sweep. Therefore, when integrating the electrolysis current separately at the opposite directions of the sweep (and provided that the potentials of the beginning and end of the integration coincide), the difference in the values of the integrals obtained will be proportional only to the content of the element being determined and will not depend on the background current of.

At the borehora b, the indicated integrals of the currents are highlighted for varying hatching — the area with vertical hatching corresponds to the current integral in the forward direction of the sweep, and the area with the horizontal shading to the width of the current in the opposite direction of the sweep. With fluctuations in the potential sweep rate, the magnitudes of the electrolysis currents at the extremum change, but the magnitudes of the 1 integrals remain unchanged, which increases the accuracy and sensitivity of the analysis. No need to measure the background current simplifies the analysis process.

The predicted method was tested by us on a number of electrochemical systems (, Fe: / Fe2fpuVPu).

As an example, the definitions of low iron contents are given.

A three-electrode cell with platinum-plus electrodes was used. The amount of iron in the cell is 2.81 μg. 1 M HCI was used as electrolyte. Potential change range

working electrode - from +200 mV to +700 mV (and vice versa) relative to a saturated calomel electrode. The sweep speed was 2 V / h. The background current under the conditions of the experiment was

10 uA. The current at the extremum points was 12.9 μA and 7.1 μA, respectively.

A class-0.1 voltage-frequency converter with an F 588 type pulse counter was used as an integrator.

The readings of the integrator in measurements under the specified conditions were 9.68 cells. Learn the known ratio

Aa

W 7

96500-l

where Vy is the amount of substance; A is the atomic weight of the element; n is the number of electrons participating in the reaction;

Q is the amount of electricity passed through the cell, the specified amount of electricity corresponds to (X 55, 84, p) the amount of iron W 2.80 µg (note: the integrator's indicator was substituted into the formula with a factor of 0.5). Pogrepsos analysis amounted to S 0.3%.

Claims (2)

1. Delakey P. New devices and methods in electrochemistry. M.-L., 1957, P.34}. 2. Skl reshoso I.S., Chebukova TM ЖАХ, 26.3, с. 4,67,1971. - E.