JPH0435706B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ion concentration meter, and more particularly to an ion concentration meter capable of accurately detecting ion concentration.

[Prior art and its problems] Conventionally, there are various types of ion electrodes, but what they have in common is that the electrode is housed in an external case, and a membrane that comes into contact with an ion-containing solution is placed in the external case. This is provided in the case.

Generally speaking, when it comes to glass electrodes, the internal electrode is housed in a cylindrical external case, a thin glass film is attached to the opening at the tip of this external case, and an internal liquid is poured into the external case. It is filled with and configured.

Further, in the solid membrane electrode, a sensitive membrane is attached to the opening at the tip of a cylindrical outer case, and the internal electrode is housed in the outer case so that the tip comes into contact with the sensitive membrane. In such a solid electrode, the outer case is not filled with an internal liquid. In other types of solid electrodes, the tip of the internal electrode does not come into contact with the sensitive membrane, and the external case is filled with an internal liquid.

In the case of a liquid film type electrode, a porous membrane is attached to the opening at the tip of a cylindrical outer case, an ion exchange liquid is stored in the outer case in contact with the porous membrane, and an ion exchange liquid is stored inside the outer case. It has a structure in which the internal liquid is filled in.

However, all of the various conventional ion electrodes with such a configuration are sensitive to the potential difference that occurs between the internal electrode inside the outer case and the reference electrode immersed in the same solution in which the ion electrode is immersed. Since the basic principle is to measure the ion concentration in the solution, for example, if the input impedance of the measurement system is high and the impedance between the electrode and the solution is also high, noise due to external electromagnetic induction may be generated. easily influenced, and
It also has the disadvantage of significant electrode contamination.

Since the sensitive membrane is attached to a separate external case or support container, the difference in expansion coefficient between the membrane and the case or container causes the membrane to be attached to the case or support container when used under high temperature conditions. and so on. Furthermore, even when used under high pressure conditions, the membrane may come off from the case or the like. Furthermore, in the case of an ion electrode that houses an internal liquid within the case, the internal liquid will leak out if the membrane comes off. In other words, the fact that the sensitive membrane and the external case are separate structures means that in the case of an ion electrode containing an internal liquid,
This shows the difficulty in maintaining a sealed state of the internal fluid.

[Object of the Invention] This invention has been made based on the above circumstances.

In other words, the purpose of this invention is to measure the ion concentration by measuring the amount of current rather than the potential difference.
Can be detected accurately. To provide an ion concentration meter that is small in size, has few causes of failure, and is equipped with an ion electrode having a structure with excellent heat resistance and pressure resistance.

[Means for achieving the above object] This invention for achieving the above object comprises forming a conductive polymer film that can be electrochemically doped on the surface of a conductive material, and applying an ion-containing solution to the conductive material. an ion electrode to be immersed, a reference electrode and a counter electrode to be immersed in the ion-containing solution, a pulse applying means for applying a potential of the ion electrode to the reference electrode in a rectangular pulse shape, and a pulse applied to the ion electrode. The ion concentration meter is characterized by comprising current measuring means for measuring the current flowing between the ion electrode and the counter electrode using a voltage.

As shown in FIG. 2, the ion concentration meter of this invention has an ion electrode 3, a reference electrode 8, and a counter electrode 9 immersed in a solution 7 containing ions. 9 is connected to a means circuitry 10 comprising pulse application means and current measurement, for example a polarograph.

As shown in FIG. 1, the ion electrode 3 is an electrode formed by forming a conductive polymer film 2 that can be electrochemically doped on the surface of a conductive material 1, thereby making it possible to generate an ionic current.

In FIG. 1, 4 is a support member that supports the conductive material 1, and 5 is a lead wire connected to the end of the conductive material 1.

The conductive material 1 is not particularly limited as long as it is a conductive material that is resistant to corrosion and does not cause electrolysis of water, such as silver, platinum, titanium, glassy carbon, graphite, etc. Examples include carbon materials such as Aite. Preferred conductive materials are platinum and the carbon materials mentioned above.

Examples of the conductive polymer film 2 include conductive polymers that can be chemically doped, and specifically, polyacetylene, poly(1,6
-heptadiyne), polyaniline, polypyrrole,
Polythienylene, poly(para-phenylene), poly(meta-phenylene), poly(para-phenylene vinylene), polypara-phenylene vinylene),
Examples include poly(para-phenylene sulfide), poly(meta-phenylene sulfide), poly(para-phenylene oxide), and derivatives thereof.

Such a conductive polymer can be manufactured by an electrolytic polymerization method. According to the electrolytic polymerization method,
A polymer film can be formed on the surface of the conductive material 1 at the same time as polymerization, and the step of adhering the once formed polymer film to the surface of the conductive material 1 with an adhesive can be omitted. Further, the thickness of the polymer film can be electrically controlled, and a uniform polymer film of any thickness can be easily formed on the surface of the conductive material 1 of any shape. Furthermore, it is important to note that by appropriately selecting the ionic species in the electrolytic solution, it is possible to create a high A molecular film can be formed. This means that ion selectivity can be easily developed in a polymer membrane by electrolytic polymerization. Therefore, it can be said that conductive polymer films obtained by electrolytic polymerization are more suitable than conductive polymer films obtained by other polymerization methods.

As mentioned above, the conductive polymer membrane in the present invention is preferably a conductive polymer membrane obtained by the electrolytic polymerization method described above, but is not limited thereto, and may be obtained by other manufacturing methods such as catalytic polymerization method. Conductive polymers can also be used.

[Function] The ion concentration meter of the present invention can measure the ion concentration in a solution as follows. That is, the potential of the ion electrode 3 is set to Ψ(t) with respect to the reference electrode 8. At this time, Ψ(t) is made into a rectangular pulse as shown in FIG. 3, for example. When this square pulse is applied to the ion electrode 3, the ions in the solution 7 are doped into the conductive polymer membrane at the ion electrode 3, and a current I( t) flows. This I(t) is
Although the current is large at the moment of the rise of the square pulse, it decreases over time and becomes a nearly constant value. Therefore, since the current I _s during a certain period of time from the rise of the rectangular pulse corresponds to the ion concentration in the solution 7, by obtaining a calibration curve between the current value and the ion concentration in advance, it is possible to The ion concentration can be determined by measuring the current value _Is .

As described above, the ion electrode according to the present invention has the following features: For example, the conductive polymer membrane is doped with ions in a solution by applying a pulsed voltage, and the doping generates an ionic current.
This method utilizes the fact that the value of the ion current is proportional to the ion concentration in the solution. Note that ion current can also be generated by immersing the polymer membrane in an oxidizing agent or reducing agent to dedope the conductive polymer membrane in advance, bringing the conductive polymer membrane into a dedoping state, and then setting the potential at which doping occurs. can be done.

[Example] Next, an example of the present invention will be shown. It goes without saying that the present invention is not limited to this embodiment.

As shown in FIG. 1, a conductive material 1, for example,
A conductive polymer film 2 with a thickness of approximately Form a 0.2 μm polypyrrole film. Note that the electrode potential during this electrolytic polymerization is +0.8 V with respect to Ag/AgCl, and the amount of electricity per unit area is approximately 70 mC/cm ² . This ion electrode, which has a polypyrrole film formed on the platinum surface and a lead wire connected to the end of the platinum, is immersed in a saline solution 7a as shown in FIG. 4.

This solution 7a contains a reference electrode 8 and a counter electrode 9.
Also soak.

The reference electrode 8 is, for example, an Ag/AgCl electrode, and the counter electrode 9 is, for example, a platinum electrode having a surface area ten times that of the ionic electrode according to the invention. The reason why the counter electrode 9 has such a large surface area is to prevent the flow of current at the counter electrode from becoming a rate-determining step.

As shown in FIG. 4, the ion electrode 3, the reference electrode 8, and the counter electrode 9 are connected to, for example, a potentiostat 11, and an ammeter 12 is connected between the potentiostat 11 and the ion electrode 3. . This potentiostat 11 is connected to a trigger circuit 13, and the trigger output from the trigger circuit 13 outputs a rectangular pulse voltage of a predetermined time width to the ion electrode 3 and the reference electrode 8 at regular intervals. A potential Ψ(t) is generated between the electrode 3 and the reference electrode 8. The output signal of the potentiostat 11 is also input to the delay circuit 14, and the delayed signal D generated by applying a certain delay is used as a gate signal to the sample and hold circuit 15. In this sample hold circuit 15, a sample signal S is extracted from the current signal I(t) outputted from the ammeter 12 using the delay signal D, and this sample signal S is outputted to the arithmetic circuit 16. The arithmetic circuit 16 stores a known calibration curve between the ion current value generated and flowing through the ion electrode 3 and the ion concentration, and calculates the ion concentration by applying the input sample signal S to this stored calibration curve. It has a configuration. A signal indicating the ion concentration output from the arithmetic circuit 16 is output and displayed as an ion concentration value on an output device 17, for example, a CRT.

The ion concentration meter with the above configuration has the following effects.

By outputting a trigger pulse from the trigger circuit 13 to the potentiostat 11 every 0.5 seconds (T), the potentiostat 11
, to the reference electrode 8, for example, T=0.5sec,
Tp=msec, Vp=1.2V (Vp1=-0.8V, Vp2=+
Outputs a square pulse Ψ(t) of 0.4V).

When a rectangular pulse Ψ(t) is applied between the ion electrode 3 and the reference electrode 8, an ion current I(t) is generated in the ion electrode 3. It is presumed that this ionic current I(t) is generated because, for example, chlorine ions in the solution 7a are doped into the polypyrrole film. In addition, applying a rectangular pulse voltage has a limit on the amount of chlorine ions that can be doped into the polypyrrole film if direct current is applied, and if all the chlorine ions are doped, the ion concentration It is presumed that this is because it is no longer possible to measure .

The ion current I(t) generated in the ion electrode 3 is measured by the ammeter 12, and is delayed by the delay circuit 13 to determine the delay time Td (for example,
The ion current I(t) at 30 msec) is sampled by the sample and hold circuit 15, and the value of this ion current _Is is sent as the sample signal S to the arithmetic circuit 16.
The arithmetic circuit 16 calculates the ion concentration according to a calibration curve as shown in FIG. 5, and the output device 17 outputs the ion concentration as data.

[Effects of the Invention] The ion concentration meter of the present invention is capable of measuring ion concentration by, for example, measuring the ion current generated by applying a pulse voltage, so that the input impedance of the measurement system is low. In addition, since the conductive material is coated with a conductive polymer film, there is less influence of interfacial potential fluctuations due to dirt, and the more accurate ion concentration can be achieved. can be measured.

In addition, since this ion electrode has an integrated structure of an ion-sensitive membrane and a conductive material, it can be made into a microstructure and can achieve improved voltage resistance, and can be used with MIS FETs, etc. Combinations are possible.

In this ion electrode, the ion current generated by application of a pulse voltage is determined by the type and amount of ion species doped or dedoped into the conductive polymer film. Since this ion species is determined by the supporting electrolyte used when forming a conductive polymer membrane by electrolytic polymerization, for example, the ion species to be measured can be freely determined by selecting this supporting electrolyte. can. Moreover, when electrolytic polymerization is employed, a conductive polymer film can be easily formed on a conductive material of any shape.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the configuration of the ion electrode according to the present invention, Figure 2 is an explanatory diagram showing the principle of an ion concentration meter that measures ion concentration using this ion electrode, and Figure 3 is this ion electrode. a time chart showing the voltage applied to and the ionic current generated;
FIG. 4 is a block diagram showing an ion concentration system according to an embodiment of the present invention, and FIG. 5 is a graph showing a calibration curve. 1... Conductive material, 2... Conductive polymer membrane, 3... Ion electrode.

Claims (1)

[Claims] 1. An ion electrode formed by forming a conductive polymer film capable of electrochemical doping on the surface of a conductive material and immersed in an ion-containing solution, and a reference electrode and a counter electrode immersed in the ion-containing solution. a pulse applying means for applying a potential of the ion electrode with respect to the reference electrode in a rectangular pulse shape; and a current measurement device for measuring the current flowing between the ion electrode and the counter electrode using the pulse voltage applied to the ion electrode. An ion concentration meter comprising means.