JPH04346066A - Ion electrode measuring device - Google Patents

Abstract

PURPOSE:To obtain an ion electrode measuring device without any leak current to an indicated electrode body regardless of insulation resistance of a sealed portion. CONSTITUTION:An ion electrode measuring device is provided with an indicated electrode 1, a comparison electrode 2, and a first amplifier 3 of a high input impedance which outputs a voltage which is logarithmically proportional to a differential voltage between the indicated electrode and the comparison electrode. A second amplifier 4 with a single gain and a high input impedance is placed between an electrode body 7 of the indicated electrode and an internal pole 6 of the indicated electrode. Since a potential of the internal pole 6 equals that of the electrode body 7 due to operation of the second amplifier 4, no leak current flows from the internal pole 6 to the electrode body 7.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electrolyte analyzer for measuring ion concentration in body fluids.

0002

2. Description of the Related Art As a conventional ion electrode measuring device, there is a device as shown in FIG. 3, for example. This device is comprised of an indicator electrode 21, a comparison electrode 22, and an amplifier 23 that outputs a voltage proportional to the potential difference between these two electrodes. The indicator electrode 21 includes an ion selective sensitive membrane 24 and an internal electrode 2.
5 and an electrode body 26, the ion selective sensitive membrane 2
4 is immersed in the test liquid 27, and the inner electrode 25 is immersed in the electrode internal liquid 28.
is in contact with. Furthermore, the inner pole 25 of the indicator electrode 21 and the electrode body 26 are adhesively sealed with an insulator at the outlet 29 of the indicator electrode. On the other hand, a conductive thin hole 30 is provided in the lower part of the comparison electrode 22, and an internal electrode 31
is in contact with the electrode internal liquid 32. Note that when measuring Na ions in body fluids with this device, a glass membrane is often used as the ion-sensitive membrane 24, and when measuring K ions, a membrane electrode containing valinomycin in PVC is often used. Often used.

Next, the operation of each part of this device will be explained.
Since an ion-sensitive membrane 24 corresponding to the ion to be measured is provided between the electrode internal liquid 28 and the test liquid 27, the indicator electrode 21
A potential logarithmically proportional to the concentration difference between the electrode internal liquid 28 and the test liquid 27 is generated at the internal electrode 25 . On the other hand, the comparison electrode 22
No potential is generated at the internal electrode 31 of. And inner pole 3
The potentials of 1 and the internal electrode 25 are respectively applied to two input terminals of an amplifier 23, and the differential voltage between both input terminals is amplified by the amplifier 23, so that the ion concentration of the test liquid can be measured as the output of the amplifier 23. It turns out.

FIG. 4 shows an equivalent circuit of this device. In FIG. 4, Ei is the electrode generated potential of the internal electrode 25. In FIG. Also, Ri is the internal resistance of the electrode,
RX is an insulation resistance value including the insulation seal 29 between the internal electrode 25 and the body 26. As is clear from this circuit diagram, the input voltage actually applied to the input terminal 23-1 of the amplifier 23 is the electrode generated voltage Ei minus the voltage drop E0 at Ri. Here, let us find the voltage drop E0 caused by the leakage current IL to the electrode body. From Figure 4, the leakage current IL is IL = E
Since i/(Ri +RX), the voltage drop (electrode loss voltage) E0 occurring across the resistance Ri is E0 = Ri
×Ei/(Ri +RX). As mentioned above, this value must be reduced, but since the internal resistance of the ion-sensitive membrane 24 is large, the internal resistance R of the electrode
i also takes a large value (several 100 MΩ to 1000 MΩ). Therefore, in order to reduce the electrode loss voltage E0, RX must be made sufficiently larger than Ri, and as a result, between the internal electrode wire and the electrode body, a highly insulating material (insulating material with an insulation value of 1000 times or more the electrode internal resistance) must be used. (resistance value is desirable) is required.

[0005]

[Problem to be solved by the invention] In the case of the conventional device, (
Although it is necessary to completely seal between the internal electrode wire and the electrode body using a highly insulating material), if insulation failure occurs due to poor adhesion, leakage current increases and electrode loss voltage E0
becomes large, and the input voltage to the amplifier becomes insufficient. In order to prevent this adhesion failure, etc.,
Advanced manufacturing technology was required to insulate and bond the lead-out portions of the internal electrodes. In addition, due to changes in insulation resistance in the first place,
Another problem is that the input voltage to the amplifier changes.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an ion electrode measuring device that does not cause leakage current to the indicator electrode body regardless of the insulation resistance value of the seal portion.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an indicator electrode, a comparison electrode, and a first amplifier that outputs a voltage logarithmically proportional to the voltage difference between the indicator electrode and the comparison electrode. In this ion electrode measuring device, a second amplifier with a single gain and high input impedance is provided between the electrode body of the indicator electrode and the internal pole of the indicator electrode.

[0008]

[Operation] A potential proportional to the concentration of ions to be measured is generated at the internal pole of the indicator electrode, and this potential is connected to the input terminal of the first amplifier. Further, the potential of the comparison electrode is applied to the other input terminal of the first amplifier. Since this first amplifier outputs a voltage that is logarithmically proportional to the potential difference between the indicator electrode and the comparison electrode, it ends up outputting a voltage that is logarithmically proportional to the ion concentration. On the other hand, the second amplifier amplifies the voltage of the indicator electrode with a gain of 1 and feeds the voltage back to the electrode body. Therefore, the electrode body and the lead wire of the indicator electrode are always at the same potential, so no leakage current flows into the electrode body regardless of the insulation resistance value of the seal portion. Further, since the first and second amplifiers have high input impedance, the current at the input terminal of each amplifier can be ignored, and therefore the potential generated at the indicator electrode hardly drops due to the internal resistance of the electrode.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit block diagram showing an embodiment of the present invention. This device includes an indicator electrode 1, a comparison electrode 2,
It consists of a high input impedance amplifier 3 that outputs a voltage logarithmically proportional to the potential difference between the two electrodes, and a high impedance single gain amplifier 4 that feeds back the output of the indicator electrode to the body of the indicator electrode.

The indicator electrode 1 consists of an ion-selective sensitive membrane 5, an internal electrode 6, and an electrode body 7. The ion-selective sensitive membrane 5 is immersed in a test liquid 8, and the internal electrode 6 is immersed in an electrode internal liquid 9.
is in contact with. Further, the internal pole 6 of the indicator electrode 1 is connected to the input terminal of the high input impedance amplifier 3 and also to the input terminal of the high impedance single gain amplifier 4. The output of this high impedance unity gain amplifier 4 is connected to the electrode body 7 via a conductive ring 10.
has been returned to. The inner pole 6 of the indicator electrode 1 and the electrode body 7 are adhesively sealed with an insulator at the outlet 11 of the indicator electrode. On the other hand, the comparison electrode 2 is provided with a conductive hole 12, and the internal electrode 13 is in contact with the electrode internal liquid 14.

FIG. 2 shows an equivalent circuit of the device shown in FIG. In FIG. 2, Ei is the electrode generated potential of the internal electrode 6. Moreover, Ri is the internal resistance of the electrode, and R1
is the resistance value between the conductive ring 10 and the seal portion 11, and R2 is the resistance value between the conductive ring 10 and the test liquid 8. The operation of this device will be explained below with reference to FIG. The electrode generated voltage Ei is applied to the amplifier 4 via the electrode internal resistance Ri.
and is applied to the input terminal of amplifier 3. Therefore, the amplifier 3 amplifies the value obtained by subtracting the voltage drop across the electrode internal resistance Ri from the electrode generated voltage Ei. On the other hand, the same voltage is applied to amplifier 4, but the voltage gain of amplifier 4 is 1. Therefore, the potential at the connection point between R1 and R2 in FIG. , R regardless of the values of e1 and R1
1, no leakage current flows. Also, amplifier 3
Since the input impedances of both amplifiers 4 and 4 are sufficiently larger than Ri, a voltage substantially the same as the electrode generated voltage Ei is amplified by the amplifier 3, and the concentration of the test liquid 8 is measured.

[0012] Although the general explanation has been given above, let us find the value of leakage current in more detail. Earlier, it was explained that the potential e1 of the seal portion 11 of the indicator electrode is equal to the potential e2 of the conductive ring 10, but more precisely, e1 and e2
A difference corresponding to the offset voltage of the amplifier 4 occurs. When considering the offset voltage value of amplifiers currently on the market, there are offset voltage values of 250 μV. In addition, the resistance value R1 between the conductive ring 10 and the seal portion 11 is set to 10
It is easy to set it to about 00MΩ. Therefore, when finding the leakage current IL using these two conditions, we find that IL
= 2.5×10-4/109 =2.5×10-1
It becomes 3A. Also, assuming that this much leakage current flows, potential loss at the ion electrode (Ri due to leakage current)
When calculating E0 (voltage drop at
As Ω, E0 = IL × Ri = 2.5 × 10-1
3 x 109 = 2.5 x 10-4V.

For reference, leakage current and potential loss are determined for the conventional devices shown in FIGS. 3 and 4. For example, Ri is 1000MΩ, Rx is 1000MΩ, and Ei is 1000MΩ.
is 0.1V, the leakage current IL is IL = Ei
/(Ri +Rx)=0.1/(2×109)=5
×10-11, and potential loss E0 at the ion electrode
is E0 = IL × Ri = 5 × 10-11 × 10
9=5×10−2V. Comparing these values with the values for the respective devices according to the invention reveals an improvement of two orders of magnitude. Furthermore, in the case of the conventional device, the potential loss E0 at the ion electrode depends on the electrode generated potential Ei and the external insulation resistance value Rx, but in the device according to the present invention, it depends only on the offset voltage of the amplifier, and other factors It also has the characteristic that it does not depend on

[0014]

As described above, in the ion concentration measuring device according to the present invention, the potential loss E0 at the ion electrode does not change even if the insulation resistance of the internal electrode lead-out portion changes. Therefore, even if the insulation resistance decreases during high humidity periods such as the rainy season, it will not be affected by this. Also,
Since the potential loss E0 at the ion electrode depends only on the offset voltage of the amplifier, advanced manufacturing technology is not required for insulating bonding of the lead-out portion of the internal pole.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing one embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the circuit of FIG. 1;

FIG. 3 is a circuit block diagram showing a conventional device.

FIG. 4 is an equivalent circuit diagram of the circuit of FIG. 3;

[Explanation of symbols]

1 Indicator electrode 2 Reference electrode 3 High input impedance amplifier 4
Unitary gain high input impedance amplifier 5
Ion selective sensitive membrane 6, 13 Internal electrode 7 Electrode body 8 Test liquid 9, 14 Electrode internal liquid 10 Conductive ring 11 Insulating seal portion 12 Small hole

Claims (1)

[Claims] 1. An ion electrode measurement device comprising an indicator electrode, a comparison electrode, and a first amplifier that outputs a voltage logarithmically proportional to a voltage difference between the indicator electrode and the comparison electrode, wherein the electrode body of the indicator electrode and An ion electrode measuring device characterized in that a second amplifier with a single gain and high input impedance is provided between an internal pole of an indicator electrode.