JPH041564A - Potentiostat for analyzer - Google Patents

Abstract

PURPOSE:To obtain a stable current value right after returning on of a power source by providing a service interruption detecting circuit which emits the signal to open a switch for an operational amplifier before the operation of the operational amplifier stops at the time of a service interruption. CONSTITUTION:The service interruption detecting circuit 8 detects the drop of the power source voltage by about 10% from an ordinary voltage as a service interruption and opens the switch 8 between a counter electrode 3 of a measur ing cell 1 and the operational amplifier 5 when such drop arises. On the other havl the operational amplifier 5 operates normally even if the power source voltage drops by about 65% from the ordinary voltage. The circuit between the counter electrode 3 and the operational amplifier 5 can, therefore, be opened while the operational amplifier 5 operates normally even if the breakage or service interruption of the power source 10 arises. The application of a reverse potential between the counter electrode 3 and working electrode 2 of the measur ing cell 1 is thereby prevented. The electrically stable state of the working electrode is protected in such a manner and the restarting of the measurement in the time as slight as 1 to 2 minutes is possible at the time of resetting after the breaking of the power source.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a potentiostat for an analyzer that performs analysis by an electrochemical method.

[Conventional technology]

One of the methods of analysis using electrochemical means is
For example, a method for measuring phosphoric acid concentration using flow coulometry is known. FIG. 3 is a schematic diagram for explaining the procedure of this method. In Figure 3, sample solution 1 containing phosphoric acid
1 and molybdate solution 12 are taken out from their respective containers by pumps 13 and 14 and mixed, and the resulting sample solution containing the phosphorus-molybdenum complex is transferred to three electrodes (not shown here): a working electrode, a counter electrode, and a reference electrode. The sample is passed through a measuring cell 15 having a

In the measuring cell 15, the potentiostat 1 connected to it
6 keeps the working electrode at a constant potential with respect to the reference electrode in the measuring cell 15, and the phosphorus-molybdenum complex is reduced on the surface of the working electrode while the sample liquid is passing through the measuring cell 15. At this time, the phosphoric acid concentration is measured by utilizing the fact that the current generated by reduction is proportional to the phosphoric acid concentration.

FIG. 4 shows a current-time diagram detected during this measurement. In Figure 4, the current value when measuring a sample liquid that does not contain phosphoric acid is the background, and the value obtained by subtracting the bank ground current value from the reduction current value when measuring a sample liquid containing phosphoric acid is the phosphorus # This is the value of reduction current that increases in proportion to 1 Ifi degree.

FIG. 5 shows an electrical circuit diagram of the main parts of the measuring cell and the Botenshi Town Stat used for the above measurements, and the power source for the whole is not shown. In FIG. 5, a measuring cell 1 has a working electrode 2. It has a 3° counter electrode and a reference electrode 4, and an operational amplifier 5 is connected to the potentiostand side connected to the measurement cell.
．． It has a circuit consisting of a potential setting power source 6 and a current-voltage converter 7 for current reading, and has a working electrode 2 with respect to a reference electrode 4.
The operational amplifier 5 operates so that the potential of The value can be read from the current-voltage converter 7 as a voltage value.

(Problem to be solved by the invention) However, during the above measurement, if the power to the Botenyostat is turned off due to a power outage, etc., even if the power is turned on again, the current value will return to the level before the power outage and it will take a long time to stabilize. This problem is shown in the current-time diagram in Figure 6.As shown in Figure 6, even if the power is turned on again immediately after a power outage, it is not stable. It takes 4 to 8 hours to obtain bank ground.Also,
In the case of an automatic total phosphorus analyzer that incorporates the above measurement principle into the device, abnormal values may occur several times after a power outage because current values higher than normal are processed as phosphorus concentration signals. The present invention has been made in view of the above-mentioned problems, and its purpose is to prevent problems such as 1t1i1! [An object of the present invention is to provide a circuit configuration of a botensistat that can quickly obtain a stable current value when re-energized.

[Means to solve the problem]

above! ! In order to solve this problem, the analyzer potentiostat of the present invention uses a switch provided in the circuit connecting the counter electrode of the measuring cell and the operational amplifier, and a signal to open the switch before the operation of the operational amplifier stops in the event of a power outage. It is equipped with a power outage detection circuit.

[Effect]

The analyzer potentiostat of the present invention, which has a circuit configured as described above, detects a power outage when the power supply voltage of the power outage detection circuit drops slightly below the normal voltage, and opens and closes the connection between the counter electrode of the measuring cell and the operational amplifier. On the other hand, since the operational amplifier 5 operates normally even if the power supply voltage is considerably lower than the normal voltage, in the event of a power outage, the circuit between the counter electrode and the operational amplifier is opened while the operational amplifier is operating normally. be able to.

Therefore, an opposite potential is not applied between the counter electrode and the working electrode of the measurement cell during a power outage, so when the power is turned on again after a power outage during measurement, the power is turned off 1 to 2 minutes after the power is turned on again. The previous output level can be restored.

〔Example〕

The present invention will be explained below based on Examples.

First, the results of experiments conducted by the present inventors to investigate the cause of the problem will be described. First, in the circuit of FIG. 5, 1. The diagram in Figure 7 shows the results of connecting an electrometer and measuring the normal potential between both electrodes and the potential when the power is turned off. As shown in Figure 7, the counter electrode 3 is usually more positive. However, when the power is turned off, the counter electrode 3 instantly becomes a negative potential. In this case, as mentioned above, it took a very long time for the current value to stabilize even after the power was turned on again. The diagram in Figure 8 shows the state of the potential between the counter electrode 3 and the working electrode 2 when the power to the Botensisstat is turned off after removing the .In this case, the potential of the counter electrode 3 is The potential did not become negative, and when the power supply 6 was subsequently turned on and the counter electrode 3 on the measurement cell was connected to the potentiostand side, the current value at this time quickly returned to the stable state before the power was turned off.

Based on these results, the present inventors found that the reason why it takes a long time for the measured current to stabilize when the power is restored after a power outage is that if a potential opposite to that at the time of measurement is applied to the measurement cell soil, it will not work until then. The electrically stable state involving the electric double layer formed on the surface of the electrode 2 is destroyed, and it takes a long time for the electric double layer to be charged again and a stable state to be formed. The conclusion was obtained.

Based on the above recognition, the present inventors improved the circuit shown in Figure 5 as shown in Figure 1 in order to prevent the reverse potential from being applied to the measuring cell soil when the power to the Botenshi Sota Stat is turned off or during a power outage. be. FIG. 1 is a circuit configuration diagram regarding the potentiostat of the present invention, and the same parts as in FIG. 5 are indicated by the same symbols, but the difference between FIG. 1 and FIG. A switch 8 installed between the operational amplifier 5 and a power failure detection circuit 9 operating the switch 8 are provided. 10 represents a power source.

The power failure detection circuit 9 detects a power failure when the power supply voltage drops by about 10% from the normal voltage, and opens the switch 8 between the counter electrode 3 on the measurement cell and the operational amplifier 5. It operates normally even if the voltage is about 65% lower than the normal voltage. Therefore, even if the power supply IO is disconnected or a power outage occurs, the circuit between the counter electrode 3 and the operational amplifier 5 can be opened while the operational amplifier 5 is operating normally, and as explained in the above experimental results, Opposite potentials are no longer applied between the counter electrode 3 and the working electrode 2 on the measuring cell.

In order to perform this operation more reliably, a charging circuit using a capacitor is built into the power supply of the operational amplifier 5, and when a power outage occurs, the operational amplifier 5
It is also possible to extend the operating time.

Figure 2 shows that during phosphoric acid concentration measurement using the potentiostat having the circuit configuration according to the present invention shown in Figure 1, when the power is turned off and then immediately turned on again, it returns to the level and maintains a stable state. It is shown that.

〔Effect of the invention〕

In analytical methods that use electrochemical reactions to perform measurements, if the power to the potentiostat is turned off during measurement, it takes a long time of 4 to 8 hours until correct measurements can be made again. However, in the present invention, as described in the embodiment, when the power is cut off due to a power outage, the signal from the power outage detection circuit is detected while the operational amplifier is operating normally. The switch installed between the counter electrode of the measurement cell and the operational amplifier is opened, which prevents the measurement cell from being exposed to a potential opposite to that during normal measurement, and protects the electrical stability of the working electrode. ,
Measurements can now be resumed in just 1 to 2 minutes after the power is turned off, and measurement errors caused by automatic analyzers can also be eliminated.

[Brief explanation of the drawing]

Figure 1 is a circuit configuration diagram of the potentiostat of the present invention, Figure 2 is a current-time diagram when the power is turned on again during measurement using the potentiostat of the present invention, and Figure 3 is a diagram of the conventional analysis method. Schematic diagram to explain the measurement procedure,
Fig. 4 is a current-time diagram for the method shown in Fig. 3, Fig. 5 is an electrical circuit diagram of the main part of the potentiostat of the measuring cell used in conventional measurements, and Fig. 6 is a diagram of the conventional potentiometer stand for power failure recovery. The current-time diagram when the power is turned on, Figure 7 is a diagram showing the potential between the counter electrode and the working electrode, and Figure 8 is the diagram showing the potential between the counter electrode and the working electrode when the potentiostat is disconnected and the power is turned off. Diagram showing potential. soil, 15: measurement cell, 2: working electrode, 3: counter electrode, 4: reference electrode, 5: operational amplifier, 6: potential setting power supply, 7: current-voltage converter for current reading, 8: switch, 9 : Power outage detection circuit, 10: Source, 11; Phosphoric acid-containing sample solution, Engineering 2:
Molybdate liquid, 13.11 pump, 16: potentiostat. Agent Patent Attorney Iwao Yamaguchi -2-5i”k No. 31! 1 Akira Dentang “Meinao 51” Part ↓ Hours [bar ff1 (h and) 2nd layer Ef!1 layer (hr) Figure 4 ＠Genki Visit Fig. 7 V Immediately after ligament rupture 5L Top Danman Fig. 8

Claims (1)

[Claims] 1) A potentiostat for an analyzer that performs analysis using an electrochemical method, which is a switch installed in a circuit that connects the counter electrode of a measurement cell and an operational amplifier, and the switch is installed before the operation of the operational amplifier stops in the event of a power outage. A potentiostat for an analyzer, characterized by being equipped with a power failure detection circuit that outputs a signal to open the analyzer.