SU399775A1 - VARIABLE WAY OF POLAROGRAPHIC ANALYSIS - Google Patents

Description

one

The invention relates to polarography and can be applied in devices for polarographic analysis — polarographs.

A known method is square wave polarography, in which a voltage consisting of a direct current voltage varying in time according to a linear law at a relatively low speed and an alternating current of a rectangular form, is used as a polarizing voltage. and measuring the variable component of the cell current at time intervals coinciding with the ends of the positive and negative half-wave voltages.

However, a square wave polarization method with a low concentration of the analyzed solution is characterized by the fact that the amplitude of the capacitive current pulses significantly (by several thousand times) exceeds the measured current of the electrochemical reaction. Therefore, the implementation of this method requires a very complex apparatus.

The aim of the invention is to increase the signal-to-noise ratio and simplify the apparatus.

To do this, the trapezoidal form is used as the alternating voltage component, which is limited to the amplitude of the spin-shaped voltage or pulses of the exponential form. The proposed method is illustrated by drawings. On fng. 1 shows a time chart.

ac voltage supplied to the semiconducting cell in a trapezoidal form of ac voltage; in fig. 2 is a time diagram of a variable component of the current of an electrochemical reaction in polarography with a trapezoidal form of a variable voltage; in fig. 3 is a time diagram of a variable component of a capacitive current in a polarography with a trapezoidal form of a variable

for women; in fig. 4 is a time diagram of the trapezoidal voltage obtained by limiting the amplitude of the sinusoidal voltage two-sidedly; in fig. 5 - timing chart

a component of the electrochemical reactivity, when trapezoidal voltage is applied to the cell, obtained by bilateral limiting the amplitude of the sinusoidal voltage; in fig. 6 - temporary

a diagram of the variable component of the capacitive current when the trapezoidal voltage is applied to the cell, obtained by bilateral limiting the amplitude of sinusoidal voltage; in fig. 7-

temporal voltage diagram of a thoracioidal form, obtained by means of a bilateral limited amplitude of pulses of exponential form; in fig. 8 is a time diagram of the variable component of the current of the electrochemical reaction when the trapezoidal voltage cell, obtained by bilateral limitation of the amplitude of the pulses of the exponential form, is applied to the cell; in fig. 9 is a time diagram of a variable component of the capacitive current when the trapezoidal form voltage is applied to the cell, obtained by means of a bilateral amplitude of the pulses of exponential form; in fig. 10 is a block diagram of an installation, with the help of which the method of polarization is realized in the event of a simultaneous voltage of trapezoidal shape.

According to the proposed method, as a polarizing voltage, a national voltage consisting of direct current voltage, time varying zon linear law with a relatively low speed, and trapezoidal alternating current voltage (Fig. I) are used and measured the variable component of the cell current at time intervals coinciding with the ends of the horizontal sections of the positive and negative half-waves of the trapezoidal voltage.

The trapezoidal voltage or tension is used as the alternating voltage, but the form is close to the trapezoidal, for example, a sinusoid bounded on both sides (Fig. 4) or an exponential form bounded on both sides (Fig. 7).

In the implementation of the proposed method, the amplitude amplitude of the capacitive current pulses to the variable component of the electrochemical reaction current during measurement is significantly less than in square-wave polarography, and therefore it is possible to use a much simpler amplifier with a controlled gain factor for amplifying the useful signal.

In square wave polarography, the amplitude of the capacitive current pulses / d is:

/with. ,(one)

where Ui is the double rectangular amplitude

voltage, / - total solution resistance

and capillary.

In the proposed method of polarography, the amplitude of the capacitive current pulses / c2 is equal to

/with. . SI, (2)

where C is the capacity of the double layer,

V is the rate of change of trapezoidal stress.

The rate of change of trapezoidal voltage is equal to the ratio of the double amplitude of this voltage to the time of its rise or fall.

The rise time (trap) of trapezoidal tension is advisable to take equal to 1/4 of the oscillation period of this voltage. therefore

 : 4f /, f, (3)

four

where U2 is double amplitude of trapezoidal voltage,

T is the period of trapezoidal voltage oscillations.

/ is the frequency of trapezoidal voltage oscillations.

Substituting (3) in (2), we get

/ pp. 4/Sh ,. (four)

Dividing (1) by (4), we obtain the ratio of the amplitudes of the pulses of capacitive current in square-wave polarography and trapezoidal polarography

Ut

If bi

/with. 4KU, Cf If the voltage amplitudes are equal, i.e., under the condition t / i f / 2, equality (5) takes the form

one

with.

/with. 4 "С / - ()

If we accept that / 50 ohm,, 5 microfarads and Hz, then

If,

- 100. //-

C2

Thus, with the accepted values of R, С -R f values, the amplitude of capacitive current pulses in trapezoidal polarography is 100 times smaller than that of square wave.

An example of the implementation of the proposed method. is a polarograph assembled but the block diagram shown in FIG. ten.

The outputs of the voltage source and voltage sources 1 with a linearly varying voltage and 2 alternating voltages are connected to the input 3 of the compensator 4, the output of which is connected to the measuring resistor 5. A cell 6 is connected in series with the measuring resistor 5. The connection point of the measuring resistor 5 and cells 6 are connected to the input 7 of the compensator 4. Measuring resistor 5 is connected to the input of the compensator 4, as well as to the input of the preamplifier 5. The output of the preamplifier 8 is connected to the input 9 of the controlled amplifier 10. The input // of controlled amplifier 10 is connected to the output 12 of the driver of 13 pulses. A controlled amplifier 10 is connected to a phase detector 14, the input 15 of which is connected to the output 16 of the driver 13 of the pulses. The phase detector 14 is connected to the recorder 17. The output 18 of the driver of the 13 pulses is connected to the input 19 of the alternating voltage source 2.

The device works as follows.

The total polarizing voltage, consisting of a slowly varying voltage provided by the source / and an alternating voltage of the trapezoidal shape from source 2, is supplied through the compensator 4 and the measuring resistor 5 to the cell 6. To provide an undistorted polarizing voltage the cell 6, the common point of the cell 6 and the measuring resistor 5 is supplied to the input 7 of the compensator 4. When the current component of the cell passes through the measuring resistor 5, a voltage drop is created on it, which then or, first, by the preamplifier 8, and then by the controlled amplifier 10 at the moment of passing the control, the pulse from the output 12 of the driver of the 13 pulses. In the pauses between pulses, the controlled amplifier 10 serves to suppress the pulses of capacitive current. The signal is then converted by a phase detector 14, to which reference pulses are output from the output 16 of the driver 13 of the pulses, from an alternating current voltage to a direct voltage proportional to the current of the electrochemical reaction. From the phase detector 14, a signal is supplied to a recorder 17. The operation of the pulse generator 13 and the alternating voltage source 2 is carried out by pumping, for which the output / S of the pulse driver 13 is fed to the input of the alternating voltage source 2.

Subject invention

Claims (3)

1. The alternating current method of polarographic analysis, which consists in the fact that. (. On the polographic cell serves for example a linear current varying in time according to a linear law, and a small amplitude alternating current voltage in which there are horizontal portions and measure the variable component of the electrochemical reaction current in the K01 horizontal portions of the half-wave of untimely nanoscapes, characterized in that In order to increase the signal-to-noise ratio and simplify the equipment, trapezoidal voltage is used as a variable component of the voltage. 2. A method according to claim 1, characterized in that, as the voltage of the trapezoidal shape, a bounded from two sides is used but the amplitude is sinusoidal for yarn. 3. The method according to claim 1, characterized in that, as the voltage of the trapezoidal shape, the pulses of exponential bounded on both sides are used but amplitude forms. email Jl Ch. : Lj Fig j v / a. S, tc Fig 8 Fig.Z