SU661321A1 - Device for registering the maximum of polarographic wave - Google Patents

Description

I

The invention relates to the field of electro-mechanical instrumentation and can be used in oscillographic instruments as an integral part of the overall design or as a separate attachment to commercially available devices.

Devices that reduce the level of residual current are known in polarography. Such devices are contained, for example, in oscillo-polarographers that implement a differential method for producing a wave, in which the residual current signal is obtained using a reference solution that does not contain the depolarizer 1 under investigation. Such devices, consisting of two identical cells and measuring channels, are quite complex, since the accuracy of their work is determined by the degree of identity of the cells and measuring channels. In addition, their use in cases where the residual current to be eliminated is caused by the presence of other electroactive substances requires the preparation of a support solution containing these substances in the same concentration as in the test solution.

this operation always takes a long time and in most cases is practically not feasible due to the lack of information on the concentration of other substances.

A known polarograph containing two cells with the test and reference solutions, a capacitor, as well as a limiter and current repeater 2. However, in this polarograph it is also necessary to have two identical cells.

Of the known devices for the formation of residual current, the invention is the closest in essence to the device, in which the residual current in the wave region of the investigated depolarizer, caused by the previous substance wave, is formed by fixing the polarizing potential at the level located between the peaks of the existing and investigated depolarizers. . It contains subtracting and registering devices, a residual current shaper, a zero-organ and a delay circuit 3. The device allows to obtain information about the wave of the investigated depolarizer taking into account the residual current on the basis of a comparison of two successively obtained polarograms. The first is removed at full sweep of the polarizing voltage and contains both the wave of the investigated depolarizer and the residual current, the second wave is removed with fixation of the polarizing voltage at the above specified level. The sequential nature of the acquisition of the programs determines the main drawbacks of the device: the practical impossibility of automating the process of comparing them (subtracting); the complexity and incompetence of the formation of a capacitive current signal after the moment of fixation of a polarizing voltage (when using an RC circuit, a constant level of capacitive current is reproduced, which also requires special adjustment during the measurement process).

The aim of the invention is to improve the measurement accuracy. The goal is achieved by introducing a differentiating and integrating device into the device, as well as a shaper of the residual current derivative, the output of the differentiating device being connected to a subtractive device and through a switch to the shaper of the residual current derivative whose output is connected to a subtractive device connected to the integrating device.

FIG. 1 shows the scheme of the proposed device; in fig. 2 is a diagram of a residual current derivative driver on an operational amplifier.

The device contains differentiating devices 1 and 2, null-organ 3 and 4, switching delay device 5, residual current derivative generator 6, subtracting device 7, integrator 8, recorders 9 and 10 of the current maximum of the analyzed wave and the potential of this maximum.

When operating the device, the following circumstances are used to record the maximum of the oscillo-polarographic wave.

In most cases, the residual current in the region of the wave being analyzed is mainly determined by the descending part of the wave of the existing depolarizer or the current of the double layer capacitance. The law of change of the downward part of an oscillo-polarographic wave is generally known and is determined by the expression

i (t) AVt + d t;

where At is a certain time interval from the moment 1 „, corresponding to the maximum of the preceding wave;

A is a constant coefficient.

The change in capacitive current in a small region of potentials (time) from the beginning of the wave to its maximum can be considered linear.

A device for recording the maximum of a polographic wave works as follows.

A measured polarographic signal is supplied to the input of the differentiating device 1. The differentiated signal from the output of the device 1 is fed to the input holographic 3 and the input of the subtractive device 7. At the moment the differentiated voltage passes through zero, corresponding to the maximum of the polarographic signal, a pulse is generated to start the delay device 5. The delay device 5, after time t, switches the switch 11 from position I to position I, and from that moment the driver 6 forms the voltage according to the law of the derivative of the residual current of the electrochemical cell. The received signal is subtracted in the device 7 from the signal coming from the output of the differentiating device 1. The obtained result undergoes an integration operation in the integrator 8. From the output of the integrator 8, the processed signal is fed to the recorder 9 maximum amplitude and differentiating device 2. The null-organ 4 at the moment of passing through the differentiated the signal from the output of device 2 through zero produces a pulse that goes to the input of the recorder 10 of the potential of the maximum of a polarographic wave, the second of which has a polarograph eskoe voltage. In position I of the switch 1 1 RC, the circuits 12 and 13 provide undistorted transmission of the signal from the input to the output of the circuit, while the voltage on the storage capacitor 14 is equal to the voltage on the input of the circuit. At the time t 0, when switching the switch to position II, the voltage at the output of the circuit is determined by the discharge of the capacitor 14 through the forming circuit, consisting of RC-links 15, ensuring the necessary law of change of the signal at the output of the device. In the open position of the key 16, the capacitor 14 is not discharged, providing a constant voltage at the output of the circuit, corresponding to a linear change in the residual current for the case when the latter is determined by the capacitive current of the cell.

The device described has, in comparison with the known ones, the advantage that it allows you to automatically determine the coordinates of the maximum oscillo-polarographic wave of the investigated polarizer taking into account the residual current using one polarographic cell with a single sweep of polarizing voltage. Its use significantly reduces the time for obtaining information on the concentration of the test substance (under appropriate conditions, the peak recorder can be directly calibrated in units of concentration of this substance).

Claims (3)

1.Bruk B.S. Polographic methods. M., 1965, p. 102 2. USSR Author's Certificate No. 505953, cl. G 01 N 27/48, 01.31.62. 3.Vestnik of the USSR Academy of Sciences. V. 32, 1962, p. 90. L.d ig. f 1rag.2