JPS6239749A - Polarization potential detection method - Google Patents

Abstract

PURPOSE:To directly detect only polarization potential regardless of the resistance of a solution, by supplying a minute DC current between the electrodes immersed in a liquid to be inspected to generate polarization potential between said electrodes. CONSTITUTION:A DC current can be supplied to a detection electrode 3 from a DC constant current apparatus 1 through a switch 2 and the supply of said current to the detection electrode 3 can be stopped. A detection part 6 can detect the instantaneous value of polarization potential. When a minute DC current is at first supplied between a pair of the electrodes 3 immersed in a liquid to be inspected, polarization potential is generated between the electrodes 3 and the magnitude thereof increases with the elapse of time and reaches a constant value determined by the composition of the liquid to be inspected beforehand. The polarization potential generated at this time appears in such a state that the potential difference caused by the solution resistance of the liquid to be inspected was superposed to real polarization potential. Hereupon, the supply of the minute DC current is once stopped in order to measure only real polarization potential and the polarization potential between the electrodes 3 is measured in a current non-supply state. By this method, because potential difference caused by solution resistance comes to zero, the polarization potential at this time is measured only as real polarization potential not affected by solution resistance.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a polarization potential detection method.

In particular, the present invention relates to a polarization potential detection method that can accurately determine the state of a test liquid, such as detecting the end point of titration.

[Conventional technology]

In coulometric and volumetric titrations, the progress of the titration -
In particular, it is important to accurately detect the end point, and many methods are known depending on the characteristics of the titration. One of them is a polarization potential detection method in which a pair of electrodes is immersed in a test liquid, a minute current is passed through the electrodes from a constant current device, and the polarization potential is measured over time. This method utilizes the phenomenon in which the polarization potential changes significantly near the end point of titration, and has been praised as an end point detection method for moisture measurement using the Karl-Fischke method.

As polarization potential detection methods, methods using direct current and methods using alternating current are known. The former has the disadvantage that the potential tends to fluctuate under the influence of stirring of the test liquid, making it difficult to determine the end point. The latter is not easily affected by stirring, but has the disadvantage that the change in polarization potential is small. This drawback can be improved to a degree by using a low frequency AC of a specific magnitude as the AC (Patent No. 93.3.3gg)
(see issue).

Also, detection 1! A method has also been proposed in which the polarization potential is detected with high accuracy by passing a pulsed direct current between the electrodes (%Gansho 5g-g5sbs).

[Problem that the invention seeks to solve]

However, in all of these methods, a minute current is always flowing between the electrodes when measuring the polarization potential.
When the solution resistance of the test liquid is large, the potential difference due to the solution resistance is superimposed on the measured polarization potential, resulting in an error.

The present invention provides a method for directly detecting only the polarization potential, regardless of solution resistance.

[Means to resolve the dispute]

That is, the gist of the present invention is to generate a polarization potential between the electrodes by passing a minute direct current between the electrodes that are immersed in the test liquid, and then to generate a polarization potential between the electrodes after stopping the supply of the minute direct current. The present invention resides in a polarization potential detection method characterized by determining the state of a test liquid by measuring the polarization potential between electrodes.

To explain the invention in more detail, in the present invention, a minute direct current is first passed between a pair of structured electrodes immersed in a test liquid. A small direct current is passed between the detection electrodes. Then, a polarization potential is generated between the electrodes, the magnitude of which increases with time and eventually reaches a constant value determined by the composition of the test liquid.

The polarization potential generated at this time appears as a potential difference caused by the solution resistance of the test liquid (solution resistance x minute direct current) superimposed on the true polarization potential. Therefore, in order to measure only the true polarization potential, in the present invention, the application of a minute direct current is temporarily stopped, and the polarization potential between the electrodes is measured in a non-energized state. As a result, the potential difference caused by the solution resistance is reduced to S of the minute DC current.
Since the polarization potential becomes zero when the current is stopped, only the true polarization potential that is not affected by the bath liquid resistance is measured.

As schematically shown in FIG. 1, a minute direct current is passed between the detection electrodes to generate a voltage Vj, and then the current is stopped once and the polarization potential is measured. When the measurement is finished,
Restart energization for the next measurement. In this way, is the polarization potential every time the current is stopped? Measure and determine the condition of the test liquid.

In the present invention, methods for determining the state of the test liquid from the polarization potential can be roughly divided into two methods: a method that uses an instantaneous value of the polarization potential, and a method that uses a time-integrated value of the polarization potential.

In the former method, after the current supply is stopped, the polarization potential gradually decreases as the first flow supply is cut off, but the polarization potential is measured at a point when the polarization potential is still sufficiently secured, and the measured value is Determine the state of the test liquid at that point. Normally, from when the power is turned off / 000 mi IJ
within seconds, preferably lO to 100 from the time of energization
After milliseconds have elapsed, the polarization potential is measured.

If the measurement time point is too early, the potential due to the influence of the dielectric constant of the test liquid will be added, resulting in an error. On the other hand, if the measurement time point is too late, the polarization potential will drop too much and become small, resulting in poor measurement accuracy.

In the latter method using the time integral value, from the time of energization stop,
The time integral value of the polarization potential is determined until the time point when the polarization potential does not decrease by much, and the state of the test liquid at this time point is determined based on this integral value. It is preferable to start the integration after the current supply is stopped and the influence of the dielectric constant of the test liquid becomes small; however, if sufficient integration time is allowed, the integration may be started at the same time as the current supply is stopped. Preferably, the polarization potential is time-integrated after at least 10 milliseconds, more preferably at least 10 milliseconds have elapsed from the time when the current supply was stopped. This method using integral values can obtain a larger and more stable signal than the method using instantaneous values described above, but if the integration time is too short or too long, measurement accuracy will deteriorate. Typically - integration time is at most 20049 seconds, preferably /o
o Mi! It is j seconds. Further, the measurement is normally completed within io oo mi IJ seconds from the time when the current supply is stopped.

In both the instantaneous value method and the integral value method described above, it is preferable to apply current immediately after the measurement is completed to restore the polarized state and prepare for the next energization stop (definition). The start time may be sufficient to ensure a sufficient polarization state between the end of the measurement and at least the next stop of energization (measurement), and the energization time is usually at least 0 milliseconds, preferably / 0
0917 seconds or more is required.

Figure 2 is a conceptual diagram of a circuit for such a polarization potential detection method.
The DC constant current device (11) is configured so that DC current can be applied or stopped via the switch (2) to the detection unit & (3). (4) is an excitation coil for driving the switch (2). 0N10FF by controller (5)
controlled. (6) is configured such that the detection section can detect the instantaneous value or time-integrated value of the polarization potential.

In the present invention, if the current is applied for the next measurement immediately after measuring the polarization potential between the electrodes, the next measurement can be carried out in a short time. Therefore, if desired, several tens of measurements can be made in 7 seconds, but normally about /-/0 measurements are sufficient.

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example: In a sealed cell chamber, 1 dehydrated solvent CM "Mitsubishi" (Mitsubishi Chemical Corporation) was added as a solvent for Karl Kuischer volumetric titration.
product) was added. A pair of detection electrodes made of white and gold wires were inserted into the cell chamber, and a button DC constant current device was connected to them.
A current of μA was applied, and the current was stopped for eo milliseconds every 5 seconds. A methanol aqueous solution was injected into the cell chamber and volumetric titration was performed. Titration is done by pulse motor
KF reagent for Karl Fischer volumetric titration is attached to the driven pump.
The potency was J~H, 07ml J was filled, and the dropping was controlled thereby. To detect the end point, the time integral value of the polarization potential during the tIo millisecond energization stop period can be easily detected without correcting the polarization potential even in the drug sample solution, and the reproducibility when titration is repeated is also good. Ta.

〔Effect of the invention〕

According to the present invention, the state of a test liquid can be accurately determined regardless of the solution resistance of the test liquid, and therefore without the need for correction, and is particularly advantageously applied to end point detection in volumetric titration.

[Brief explanation of drawings]

Figure 1 schematically shows the relationship between the application and stopping of direct current to the detection electrode and the generation of polarization in the present invention. The upper row shows the current, the middle row shows the polarization generation potential, and the lower row shows the polarization. Measuring potential? show. FIG. 1 is a conceptual diagram of a circuit of a polarization potential detection device suitable for carrying out the present invention. (11 DC constant current device (21 switch (3)) Detection electrode (4; Excitation coil (5 (controller) (6) Detection unit Patent applicant Mitsubishi Chemical Industries, Ltd. agent Patent attorney Hase - 1 other person

Claims (6)

[Claims] (1) A minute direct current is passed between the electrodes immersed in the test liquid to generate a polarization potential between the electrodes, then the minute direct current is stopped, and then the polarization potential between the electrodes is generated. A polarization potential detection method characterized by determining the state of a test liquid by measuring the potential. (2) The polarization potential detection method according to claim 1, characterized in that the polarization potential is integrated for a certain period of time every time the current supply is stopped, and the state of the test liquid is determined based on this integrated value. (3) Polarization according to claim 1, characterized in that the polarization potential is measured after a certain period of time after the energization is stopped each time the energization is stopped, and the state of the test liquid is determined based on this measured value. Potential detection method. (4) The polarization potential detection method according to claim 2, characterized in that the polarization potential is integrated within 200 milliseconds from the time when the current supply is stopped to 1000 milliseconds. (5) The polarization potential detection method according to claim 3, characterized in that the polarization potential is measured within 1000 milliseconds after energization is stopped. (6) The determination of the state of the test liquid is a determination of whether the test liquid has reached the end point of titration. polarization potential detection method.