JPS58108447A - Measuring electrode for carbon dioxide gas - Google Patents

Abstract

PURPOSE:To provide a measuring electrode which miniaturizes a pH-sensitive member, has a low impedance, is difficult to ride on noise, is excellent in strength, and has a rapid answering speed, by using a pH electrode in which a thin pH-sensitive film is formed as a pH electrode on a semiconductor substrate. CONSTITUTION:If a portion of a gas permeable film 25 at a point of a measuring electrode 21 is immersed in liquid to be measured, gas dissolved in the liquid to be measured permeates the permeable film 25, and moves to an external electrolyte layer 38 side. Carbon dioxide gas moving to the external electrolyte layer 38 reacts with water in an external electrolyte 26 and is brought into a balancing state. An H<+> ion changes pH of the external electrolyte layer 38. It is selectively sensed by a pH-sensitive film 28 of a pH electrode 36, and a difference in phase field potential corresponding to pH is caused at an interface between the pH-sensitive film 28 and the external electrolyte 26. The difference in potential is amplified by an external potential detector, and a carbon dioxide gas concentration is found by operating a computing element.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention VI4 relates to a carbon dioxide gas measuring electrode for measuring carbon dioxide gas dissolved in a test liquid such as TFJK liquid.

BACKGROUND ART One means of testing the metabolic function of a living body is to measure the vertical concentration of acid gas (partial pressure of carbon dioxide) dissolved in blood. To determine this carbon dioxide concentration #1, use φ
What is used is a carbon dioxide measuring electrode. Conventionally, severe ring hax (S to T inhibit NGHALT8) was used as this kind of electrode.
) is known as ``A Symposium''.
On p)I and BloodGas M@as
ur@ment JP 124i ~ 142, J &
A.

Churchill Ltd, 19541. As described in detail in Figure 1, the structure of the severe ring house type carbon dioxide gas pumping electric current &l is shown.

That is, this carbon dioxide measuring electrode 1 is placed at the tip of the outer cylinder 2,
A gas permeable membrane 4 attached with an O ring S, an external electrolyte 5 housed in the outer cylinder 2, a nine pH electrode 6 immersed in the external electrolyte 5 in the outer cylinder 2, and a reference electrode 1. It consists of The gas permeable membrane 4 #i allows the dissolved gas in the test liquid to pass therethrough, but does not allow water or ions to pass therethrough. The external electrolyte used is, for example, a dilute solution of sodium bicarbonate, which reacts with the carbon dioxide gas that has passed through the SFi gas-permeable membrane 4 and changes its pH. t, F inside this outside mastj
i As will be described later, in order to maintain the potential of the reference electrode 1 at a constant concentration when using an Ag/AgCj electrode as the reference electrode 1, a chloride such as NaCj is added at a constant concentration t.
Ru. Reference electrode 1 is a wire-like surface of an iron wire formed by MCI.
It is electrolyzed in a solution to form silver chloride, and its potential does not change even if the pH of the external electrolyte 5 changes.

A well-known pH-sensitive glass membrane 9 is stretched over one end of the GFi inner tube 8, and a phosphoric acid aS solution with a constant pH or the like is placed inside the inner tube 8 to maintain electrical contact with the pH-sensitive glass membrane 9. An internal electrolytic solution 10 consisting of the above-mentioned internal electrolytic solution 10 and an internal electrode 11 consisting of an Ag/AgCj electrode are arranged so as to maintain electrical contact with the internal electrolytic solution 10.

This pH-sensitive glass 9 with a pH of 11&g and the gas permeable membrane 4 are arranged to face each other with a hydrophilic substrate 12 such as cellophane interposed therebetween. The external electrolyte 5 enters the spacer 12 to form an external electrolyte layer JJ.

Therefore, the gas permeability 1j, 4 of this carbon dioxide measuring voltage &l
For example, when immersed in a test liquid such as blood, the gas permeable membrane 4Jd permeates along the test sample and only nine gases permeate into the external electrolyte layer 51m, but the test liquid and ions, etc. Don't let it pass through. The permeated carbon dioxide reacts with water in the external electrolyte layer IJ to reach an equilibrium state as shown in the following equation.

COI +l(,0';i H* COI, H+n
col'' The 9H ions produced by this reaction change the pH of the external electrolyte layer I3, which is selectively sensitized by the pH-sensitive glass membrane 9 and causes the pH-sensitive glass membrane 9 to interact with the external electrolyte WjL layer I3. A nine-phase field potential difference occurs at the interface depending on the pH.This potential difference is applied to the internal 1
1[@lr, and a potential difference is generated between this internal electrode 11 and the reference turtle &7 according to its pH. Therefore, this potential difference is measured by an external potential detection device, and the carbon dioxide concentration is indirectly known from the result.

However, since such a conventional carbon dioxide measuring electrode l uses a pH-sensitive glass membrane 9 as the pH electrode 6 for detecting changes in pH of external electrolysis @i, the appearance of the carbon dioxide measuring electrode l is unavoidable. When the size becomes large and a large amount of sample liquid such as blood is required for measurement, there is a disadvantage of φ. This is the pkl l of pH electrode 6 & reaction glass membrane 9
Although it can be improved to some extent by making it smaller,
If the pH-sensitive glass membrane 9 in step 7 is made smaller, the resistance will be significantly higher, which will easily induce noise and make accurate measurements impossible.
This causes a serious inconvenience. In addition, by making the pH-sensitive glass very thin, its resistance can be lowered, but since the material is glass, its mechanical strength decreases, making it unusable.Furthermore, as mentioned above, the internal Since the internal electrolyte 10 is stored in the
It is possible to reduce the size beyond a certain level, and as a result,
The carbon dioxide gas adjusting electrode l containing the pH electrode 6 had to be large in size.

The present invention has been made in view of the above-mentioned circumstances, and aims to achieve miniaturization, low impedance and low noise resistance, and excellent mechanical strength. The object of the present invention is to provide a highly responsive acid gas measuring electrode.

That is, the present invention provides a leg acid gas measuring electrode comprising a gas permeable membrane, an electrolytic solution, a PHt electrode, and a reference electrode.
The present invention is characterized in that at least one of an aluminum oxide film and a tantalum pentachloride film is formed, and this film serves as an ion-sensitive film that is selectively sensitive to changes in pH.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. 2 and gao.

FIG. 112 shows a vertical acid gas measurement electrode 21 according to this refreshing example, which is equipped with an outer cylinder 22 and an inner cylinder 23 disposed coaxially inside the outer cylinder 22. The gas permeable membrane 2Ii attached to the #i open OS under the tube 2z with the ii O-ring 24 is spread out. Gas permeable membrane; t
aFi is made of a gas-permeable and hydrophobic synthetic resin film such as Teflon resin or silicone resin),
It selectively allows only the gas dissolved in the test liquid to pass through, but does not allow water or ions to pass through.

Inside the outer cylinder 21, an external electrolyte 11iZ6 whose pH changes by reacting with carbon dioxide gas that has passed through the gas permeable membrane 26 is accommodated. This external electrolyte 26 is made of a dilute solution of sodium bicarbonate, etc., and acts as a trap to maintain a certain pH value even when gas does not pass through. Further, the external electrolyte 26 contains a chloride such as NaCj at a constant concentration in order to keep the potential of a reference electrode, which will be described later, constant.

As will be described later, a pH sensitive film 28 is formed on a silicon substrate zr at the lower end opening of the inner cylinder 23, and a pH sensitive member z9 is pasted or fused thereon. 26. Said pH sensitive member 29: As shown in the figure 183, on a conductor substrate, for example, a silicon substrate 21, a conductor, silicon oxide (81s Na
) A film consisting of at least one of commercial aluminum (AjtOs) and tantalum pentoxide (TaOs) is deposited by vacuum evaporation, sputtering, or CVD (
Ch@m1cal Vapor Depositio
The pH-sensitive film 28 is formed by forming the film by a method such as n).

Furthermore, the back surface of the silicon substrate 21 is connected to the core wire 3S of the lead wire 3z via a conductive resin (adhesive) JJ. In addition, when soldering the core wire 32 of the lead wire 3z, since it cannot be soldered directly to the silicon substrate zrK, as shown in FIG. The electrode FtII 34 is evaporated, and the Cr-Cu electrode 1@35 is further soldered thereon by evaporation. The inner tube 713, the pH sensitive member 29, and the core wire 33 of the lead wire 32 form a pHt 436, and the phlegm that occurs in the pH sensitive layer 28 of the ant pH sensitive member 29 can be detected.

Further, in the outer cylinder 2z, an aqueous spacer 31 made of cellophane or the like is interposed between the gas permeable membrane 25 and the pH sensitive member 2# as necessary. Then, a part of the external electrolyte z6 penetrates into the hydrophilic space tsr, thereby forming an external electrolyte layer J8 between the gas permeable membrane 25 and the pH-sensitive Nxs. -ru.

Furthermore, a FipH1 pole 36 and a pole side 6 reference electrode J9 are provided in the outer cylinder z2 with one end thereof immersed in the external electrolyte 26. This reference electrode 39 is formed in the shape of a wire and has a silver rim, and the electrode 39 is made of silver chloride by electrolysis in an HCj solution. The potential at this reference electrode 39 is determined by the potential of NaCj in the external electrolyte 26 as described above.
Chlorides such as are constant l! Rounding included in I degrees is constant.

When measuring the carbon dioxide concentration in a sample liquid such as blood using the carbon dioxide measuring turtle & 2J constructed in this way, the gas permeable membrane 250 at the tip of the carbon dioxide gas measuring turtle 2J as described above is used.
The part is immersed in the test liquid. Then, the residue dissolved in the test liquid passes through the gas permeable membrane z6 and moves to the IAs electrolyte layer 38 side. Note that the test liquid, ions, etc. do not pass through the gas permeable membrane 25.

Further, the gas that permeates is not limited to only carbon dioxide gas, but other gases dissolved in the test liquid, such as O and gas, permeate, but gases other than carbon dioxide gas do not participate in the following reaction.

The carbon dioxide gas transferred to the external electrolyte layer 38 reacts with the water in the external electrolyte 26 to reach an equilibrium state as shown in the following equation, as described above.

COI + n, 0 nmcoa; n + l (CO
Then, the H ions produced in this reaction are sensitive to , and Fi is generated at the interface between the pH-sensitive material z8 and the external electrolyte 26.
A phase field potential difference occurs depending on pHK. This potential difference is applied to the lead @aX through the silicon substrate 2r and the conductive resin 31.
It is transmitted to the core wire 33, and this core wire 3J and the reference voltage @, :I9
Depending on the pH value in the external electrolyte layer 38, a 19-potential difference appears between the two. And the pH change of 7 tl Henderson-Hasselpal lk (HEND
ER-8ON-HASSELJIAL, CM) O
From the formula, log P C (h K is known to be proportional. Therefore, it is possible to calculate the carbon dioxide concentration by amplifying the above potential difference using an external potential detection device) and calculating it with a calculator. can.

By the way, as described above, the pH sensitive film 28 of the pH electrode 36 is formed on the silicon substrate sr by vacuum evaporation, sputtering, CVD, etc., and these films can be formed extremely thin and uniformly. It7t,
The reason for limiting the pH-sensitive film thickness is that if the thickness of the pH-sensitive film 18 is less than 5ooX, the thickness becomes uneven and defects such as pinholes are likely to occur, resulting in a rapid increase in yield 9. At the same time, durability also suffers.

Furthermore, if the pH-sensitive film 28 is made thicker than 500 OA, the impedance of the pH-sensitive film z8 will increase the noise, and the response speed will become slow.

Silicon substrates; TR, FI are commonly used in the semiconductor industry, and are characterized by being inexpensive and allowing for a mirror finish with very little unevenness on the surface due to etching. Furthermore, silicon ice plate 27
serves as a substrate for the pH-sensitive film 28 and increases its mechanical strength, and also serves to transmit the phase field potential difference generated in the pH-sensitive film 28 to the core @3111C of the lead wire 32. Therefore, in this case, the silicon substrate z yFip!
I! Any lead flea of a certain %fhtin type may be used,
Moreover, it may be single crystal or polycrystalline. pH sensitive membrane 2#
As mentioned above, the silicon substrate 21 must be formed very thin and uniformly, but since the silicon substrate 21 can be easily mirror-finished, it has a good pHJ without pinholes.
11 layer film 21 can be formed on the silicon substrate 17.Furthermore, since the silicon substrate 21 can have any thickness, its mechanical toughness can be increased.

As explained above, according to the present invention, the pH of the external electrolyte
Since a thin pIi sensitive film formed on a semiconductor substrate is used as a PHIK electrode for detecting changes in pH, the pH sensitive member portion can be made smaller, and its impedance is low and noise is less likely to occur. Furthermore, it is possible to provide a carbon dioxide measuring electrode with excellent mechanical stiffness and a fast response speed.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional liN & gas 1llj constant electrode.
FIG. 2 is a cross-sectional view of one embodiment of the present invention, FIG. 183 is a cross-sectional view of a pH-sensitive member in the same embodiment, and FIG. 4 is a cross-sectional view of a pH-sensitive member as another embodiment. 21... Carbon dioxide gas measuring electrode, 26... Gas permeable membrane,
26...External electrolyte, zy...Silicon substrate, 28
...pH sensitive membrane, 36...pHt pole, 39...reference electrode O Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 211 jI3 Figure 41

Claims (1)

[Claims] Gas-permeable glands that are dissolved in the sample liquid and selectively permeate only nine gases, and this gas-permeable membrane? The electrolytic solution whose PR changes by reacting with the gas that permeates through it, and the φH of the electrolytic solution
A pH1 electrode that responds to changes in the electrolyte, and a reference electrode that is partially inserted into the electrolyte, and the pH1 electrode is formed of a silicon nitride film, an aluminum oxide film, an aluminum oxide film, and a rum pentoxide film on a semiconductor substrate. At least one tantalum film acid gas #j constant electrode.