JPH021537A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To decrease the drift at the time of use in a flow system and external circulation system by confining the surface area of an oxygen sensitive part consisting of a porphyrin deriv. compd. and the metal complex compd. thereof with which a conductive base body is coated. CONSTITUTION:PBG 1 formed by bundling carbon fibers which have the circular shape of about 6mum diameter in the section of one piece and have 2.0cm length is used as the conductive base body. A lead wire 3 is adhered by a conductive adhesive agent 2 to this base body. The base body is coated circumferentially with an epoxy adhesive agent and a 'Teflon(R) tube 5 having 1mm inside diameter, by which the base body is insulated and only the section of the PBG 1 is acted as an electrode surface. This electrode surface is coated with an electrolytically polymerized film 6 of meso-tetra (0-aminophenyl) cobalt porphyrin as an oxygen sensitive part. The PBG 1 is coated with a silicone tube 9 filled with an aq. 10% polyvinyl alcohol soln. 8 and is fixed and insulated with a thermo plug 10 and an urethane adhesive agent 19.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an oxygen sensor, especially a membrane that has small drift (stability of current density) and can measure oxygen concentration over a wide range in extracorporeal circulation systems, flow systems, etc. This invention relates to a coated solid-state oxygen sensor.

[Prior art] Conventionally, silver/silver chloride was used as a reference electrode and platinum or platinum black was used as a working electrode, which was immersed in an alkaline solution such as potassium hydroxide (NI011), and the outside was covered with a silicone film. A Clark-type oxygen sensor with a similar shape is on the market.
Miniaturization in terms of shape and improvement in durability are required from the viewpoint of continuous monitoring in the circulatory system.

Recently, coated oxygen sensors have been developed in which cellulose membranes and other polymer membranes are directly coated on platinum electrodes.
re type) is on the market as a test sensor. These sensors have problems with durability, and their usage time is extremely short in areas with high Po2 (350 mmHg or higher), such as when an oxygenator is attached.

The present inventors have proposed an oxygen electrode that directly coats a porphyrin derivative compound and its metal complex compound on a conductive substrate, a reference electrode, and an oxygen sensor that addresses the above-mentioned problems.
We have previously filed an application for a Clark-type solid-state oxygen sensor comprising a gel-like polymer electrolyte impregnated with the oxygen electrode and reference electrode, and an oxygen selectively permeable membrane covering the gel-like polymer electrolyte (Patent Application No. 6).
(No. 2-71833) However, the sensor had a problem in that it caused drift in the circulatory system.

[Problems to be Solved by the Invention] An object of the present invention is to solve the problems of the prior art described above, and to provide an oxygen system that has small drift and can be measured over a wide range of oxygen concentrations when used in a flow system or an extracorporeal circulation system. The purpose is to provide a sensor.

[Means and effects for solving the problem] The oxygen sensor of the present invention that solves this problem includes an oxygen-sensing section consisting of a conductive substrate and a porphyrin derivative compound and/or a metal complex compound thereof that coats the conductive substrate. The oxygen sensor is characterized in that the surface area of the oxygen sensing portion is sized to be equal to or less than a predetermined drift value.

Preferably, it is carried out as follows.

1. Drift is 5 x 10-5 A/Cm2 or less.

2. The conductive substrate is conductive carbon.

3. Carbon materials are carbon fibers and carbon rods.

4. The cross-sectional area of the carbon material is 10-'am2 or less.

5. In an oxygen sensor with an electrode configuration in which an oxygen electrode, a reference electrode, and a counter electrode are impregnated with a gel-like polymer electrolyte, and the outside is covered with an oxygen selectively permeable membrane, the area of the sensitive part of the oxygen electrode can be increased to 8.5810 -'cm2.

6. Porphylymph conductors are meso-phenyl derivatives.

7. The metal that forms the porphyrin complex is Fe, Co
, Ni.

8. The metals forming the porphyrin complex are transition metals such as titanium, vanadium, chromium, manganese, copper, ruthenium, rhodium, palladium, iridium, platinum, silver, and gold, or zinc and tin.

9. The porphyrin compound is selected from porphyrin compounds having a hydroxy aromatic semiconductor device substituted at the meso position and porphyrin compounds having an amino aromatic semiconductor device substituted at the meso position.

10. The metal complex of the porphyrin compound is selected from a metal complex of porphyrin substituted with a hydroxy aromatic solid conductor at the meso position and a metal complex of porphyrin substituted with an amino aromatic semiconductor device at the meso position.

[Example] The present inventor previously used as a coating film an oxidatively polymerized film of a porphyrin compound having a phenyl group having an active group such as OH or NH2 as a substituent, or a complex having this as a ligand. It has been found that by doing so, an oxygen electrode with excellent selectivity and in which membrane components are difficult to elute can be obtained.

First, this oxygen electrode will be explained. This oxygen electrode is
An oxygen sensor comprising an electrically conductive substrate and an electrolytic oxidative polymer film covering the surface of the electrically conductive substrate, wherein the electrolytic oxidative polymer film is made of at least one substance selected from porphyrin compounds and metal complexes thereof. It is characterized by

As the conductive substrate used in this oxygen electrode, conductive carbon is suitable, and examples of the conductive carbon include basal brane pyrolytic graphite (basal brane pyrolytic graphite).
al plane pyrolytic graph-h
(hereinafter referred to as BPG), glassy carbon, and the like.

Suitable porphyrin compounds for use in this oxygen electrode include porphyrin compounds in which a hydroxy aromatic semiconductor device is substituted at the meso position and porphyrin compounds in which an amino aromatic semiconductor device is substituted at the meso position.

Further, as the metal 211 body of the porphyrin compound suitable for use in this oxygen electrode, there are metal complexes of porphyrin in which a hydroxy aromatic semiconductor device is substituted at the meso position, and metal complexes of porphyrin in which an amino aromatic semiconductor device is substituted at the meso position. Can be mentioned.

In addition, as a porphyrin compound with a hydroxy aromatic conductor or an amino aromatic semiconductor device at the meso position,
The following formula (R+)h (R1).

(In the formula, Ar is aromatic, R is a substituent during electrolytic oxidative polymerization, R2 is a substituent that does not react during electrolytic oxidative polymerization, n is 1 to the effective valence of Ar, and m is 0 to the effective atom of Ar. Examples include tetra-, tri-, di-, or mono-(hydroxyphenyl)porphyrin represented by the formula (-1) and tetra-, tri-, di-, or mono(aminophenyl)porphyrin. The substitution positions of hydroxyl group and amino group are ortho position,
The para position is preferred, and hydroxyl groups, amino groups, or other substituents may be further substituted at other positions.

A metal complex of porphyrin in which a hydroxy aromatic derivative or an amine aromatic semiconductor device is substituted at the meso position is expressed by the following formula, with one or less spaces (in the formula, Ar is an aromatic group, R1 is a substituent of electrolytic acid polymerization, R2 is a substituent that does not react with G during electrolytic oxidative polymerization,
M is a complex-forming metal, in principle nB±1 or effective valence of Ar, m is O5s, effective valence of Ar-1
shows. ) Tetra, tri, di-or (mamono(hydroxyphenyl)porphyrin epsilon), tetra, tri,
Di- or mono(aminophenyl)porphyrin complexes are mentioned as preferred.

Metals that form complexes include titanium and vanadium.

Chromium 9 Manganese, Iron, Cobalt, Nickel.

copper, ruthenium, rhodium, palladium, osmium,
Transition metals such as iridium, platinum, silver, and gold, as well as zinc and tin, among others, include cobalt, nickel, iron,
Particularly preferred are copper, manganese, chromium and platinum.

In order to deposit an electrolytically polymerized film of a porphyrin compound or a metal complex thereof having a hydroxy aromatic derivative or an amino aromatic semiconductor device substituted at the meso position on the surface of a conductive carbon substrate,
Electrolytic oxidative polymerization may be carried out by immersing the conductive carbon substrate in an electrolytic solution containing at least one of the above-mentioned porphyrin compounds or metal complexes thereof, such as a supporting electrolyte. Examples of the solvent used in the electrolyte include acetonitrile, methanol, dimethylformamide, dimethyl sulfoxide, propylene carbonate, etc., and examples of the supporting electrolyte include perchlorate, sulfuric acid, phosphoric acid, boric acid, potassium tetrafluorophosphate, 4R, ammonium salts are preferred. The electrolytic oxidation polymer film has a thickness of 100λ to 1
It is preferable to set it to 00 μm. Especially 0.01~50μm
Good.

The electrolytically oxidized polymer film thus deposited is dense and difficult to dissolve into the test liquid, so it can usually be used without further depositing a film thereon.

However, when measuring in body fluids (blood, urine, etc.), a regenerated cellulose membrane, acetyl cellulose, polystyrene, polyhydroxyethyl methacrylate, etc. is added on top of the membrane to prevent protein adhesion and reducing substance permeation. It is particularly preferable to use it by adhering it. The film thickness is preferably 0°5 to 50 μm.

This electrolytically oxidized polymer film is oxidized when it comes into contact with oxygen, so if a constant potential is applied using this oxygen sensor as a working electrode, a current based on the reduction reaction of oxygen on the electrolytically oxidized polymer film can be observed. be done. Therefore, if the correlation between the oxygen concentration in the standard solution and the observed current value is determined in advance, the oxygen concentration can be determined from the observed current value in the test solution.

The potential applied to the working electrode varies depending on the type of volufuirne compound or its complex used for the coating film and the film forming method.

Since this oxygen electrode has the above-mentioned configuration, it has the following advantages.

(1) Since it is a solid-state membrane-coated electrode that does not use an internal liquid, there is no need for complicated operations such as contamination of the internal liquid and its replacement, as with conventional internal liquid chamber type electrodes (Clark type electrodes).
Moreover, it can be made smaller.

(2) Since the electrode base material is conductive carbon, it is cheaper than conventional electrodes using noble metals. Therefore, it is suitable for disposable use.

(3) The electrode substrate (conductive carbon) is directly coated with a polymer film of oxygen-reducing reactive species (porphyrin) produced by electrolytic polymerization, so it is different from the conventional polymer membrane that supports oxygen-reducing reactive species. It has the following features compared to coated electrodes.

(2) The concentration of oxygen-reducing reactive species in the film can be increased and a dense film can be formed, so a thin film can be used and the response time to oxygen can be shortened.

■ Excellent selectivity for oxygen due to low uptake of interfering substances.

(2) Since the membrane itself has solvent resistance, the metal complex does not elute into the test liquid, so there is generally no need to additionally apply other elution-preventing membranes, and the structure is simple.

■ It can be stored in a dry state and can be used immediately after storage, allowing immediate measurement of oxygen concentration.

<Example 1> In this example, the above-mentioned oxygen electrode in which a porphyrin derivative compound and its metal complex compound were directly coated on a conductive substrate, a reference electrode, and an ion conductive material impregnated with the oxygen electrode and the reference electrode were prepared. An oxygen sensor including an electrolyte as a body and an oxygen selectively permeable membrane covering the electrolyte will be described.

The oxygen selectively permeable membrane used in this example is made of a hydrophobic polymer membrane such as silicone, polypropylene, polyethylene, or Teflon.

The electrolyte as the ionic conductor used in this example is preferably one made of a gel-like polymer, including phosphate Ni
An aqueous polyvinyl alcohol solution containing street liquor and sodium chloride is particularly suitable.

Further, a suitable conductive substrate used in this example includes a conductive substrate. Preferred porphyrin derivatives used in this example include meso-phenyl conductors, and preferred porphyrin S11 derivatives include Fe, Co,
Examples include Ni.

(Preparation of oxygen electrode) The oxygen electrode shown in FIG. 1(b) was prepared by the following method. This will be explained below with reference to FIG. 1(b).

One cross section has a circular shape with a diameter of 6 μm, and the cross-sectional area is 2.82
A conductive substrate 1 was made of a carbon fiber having a length of 2.0 cm (6×10 −9 cm 2 ) and a length of 2.0 cm, and a lead wire 3 was adhered thereto using a conductive adhesive 2 (manufactured by Cylon B Atsugi Research Institute Co., Ltd.). Apply epoxy adhesive 4 around it.
It was then covered with a Teflon tube 5 having an inner diameter of 1 mm for insulation, so that only the cross section of the carbon fiber 1 served as the electrode surface. The surface of this electrode was coated with meso-tetra(O-aminophenyl)cobalt porphyrin electropolymerized 11i6 as an oxygen-sensitive part under the electrolytic conditions shown below.

Electrolyte composition: Meso-tetra(0-aminophenyl)cobalt porphyrin...1 mmol/u Sodium perchlorate...0.1 mou/fLi volume! i. Niacetonitrile electrolysis conditions: In the above electrolyte, the carbon fiber electrode was used as the working electrode, A
g / A g Using the CIt electrode as the reference electrode and the platinum winding as the counter electrode, +1.8V (vs.
, Ag/AgC) for 60 minutes.

(Preparation of reference electrode) A silver wire 7 on which AgCjiL was deposited by electrolysis was wound around the Teflon tube 5 of the carbon fiber electrode to serve as a reference electrode and a counter electrode in the oxygen sensor.

(Production of Oxygen Sensor) A schematic diagram of the configuration of the oxygen sensor is shown in FIG. 1(a). Carbon fiber electrodes and Ag/AgCn electrodes were mixed with a 10% polyvinyl alcohol aqueous solution 8 (50 mmon) as an electrolyte.
/J2 pH 7,38 phosphate buffer, 0.154 mo
silicone tube 9 (inner diameter 2 mm, pressure 015 mm, surface pressure O/J) filled with
1 mm), and the surrounding area was covered with thermo plug 10
．． Fixed and insulated with urethane adhesive 19, and oxygen sunner 20
completed.

Incidentally, conductive carbon is suitable as the conductive substrate, and examples thereof include basal plain pyrrolitic graphite, glassy carbon, etc. Among these, those having a graphite structure are particularly preferred.

<Experimental Example 1> FIG. 2 shows an example of a circuit for measuring oxygen partial pressure using the oxygen electrode and reference electrode produced in the example. Here, 21 is an electrolytic cell, 22 is a test liquid, 20 is an electrode, 24 is a gas injection tube, 25 is a 0.6V DC power supply, and 16 is a DC ammeter.

Using this measurement circuit, the number of carbon fibers (?l
! The current density was measured while changing the polar area. A 50mM phosphate buffer containing 0.154M NaC1 was used as the test solution, and this solution was mixed with a gas injection tube at a known mixing ratio (e.g., 02 concentration 18% at 37°C, approximately 40%
(equivalent to mmHg), and the value of the current flowing at that time was measured with a DC ammeter. The warping results are shown in Table 1. here,
Area ratio 1 is 500 carbon fibers, 2 is too.

Trees, 4 is 2000 trees, 6 is 3000 trees, 1o is 5000 trees
Book, 20 indicates that it is a toooo tree.

In this example, the cross-sectional area of the carbon fiber is changed, but this is to change the surface area of the oxygen sensitive part that comes into contact with the test liquid, and in the oxygen sensor configured in this example, the carbon fiber is The cross-sectional area of and the surface area of the oxygen-sensitive portion approximately correspond to each other. This is because the film thickness of the porphyrin compound is as thin as 100 μm to 100 μm.

It is clear that even if the configuration of the oxygen sensor changes, the surface area of the oxygen sensing portion corresponds to the stability of the drift current density.

Margin below 1 From Table 1, the cross-sectional area of carbon fiber is 1.413xl
Within the range of O-'am2 to 2.828x10-3am2, from 3.30X10-5A/cm2 to 5.1 x 10
A current density of -5 A/cm' was obtained.

Next, in an external circulation circuit system using an oxygenator shown in FIG. 3, the relationship between flow rate and current density was measured while adjusting the oxygen density to a constant 140 mmHg and 37° C.±0.05° C. Here, 17o is an oxygenator, 171 is a constant temperature bath, 172 is a heat exchanger, 173 is a roller pump, 174 is a reservoir, 175
17 is a flow-through cell in which the enzyme sensor 20 is set;
6 is polarographic (ponARoaRAp+
uC) ammeter, 177 is an enzyme concentration measuring device, 178 is an arithmetic processing unit, polarographic ammeter 176
The enzyme concentration measuring device 177 is connected to an optical fiber 179.

As shown in Figure 4, the experimental results show that although the current density increases somewhat as the flow rate changes, when comparing the flow rates of 250 m111 min and 1200 mn/min, the difference is 0.
This is a minute current change of I x 10-5 A/cm'. The relationship between the electrode area and current density under the condition of a constant flow rate of tooomi/min is shown in Table 1 with a cross-sectional area of 1.413 x 1
When 0-'am2 is set to 1, it can be obtained as shown in Table 2 below.

Table 2 The result is '2i! It has become clear that the current density hardly changes when the polar area, that is, the surface area of the oxygen sensitive part is about six times larger.

Experimental Example 2 Using the oxygen partial pressure concentration measuring circuit shown in Figure 2, the stability (drift) of the current density of this oxygen sensor was measured for 30 minutes while stirring at a stirring speed of 300 rpm using a stirring bar. Figure 5 shows the results of continuous measurements over the period of time.

As a result, the electrode area, that is, the surface area of the oxygen sensitive part is 5.
When it is less than 65xlO-'am2, there is almost no drift. However, a drift is observed when the value is 8.478x10''am2 or more.

It was confirmed that this tendency tends to increase as the electrode area increases. Therefore, the electrode area, that is, the surface area of the oxygen sensitive part is s, asxio"" cm2 ~ 8.47
Between 8X 10-'am2 (equivalent to 2000 to 3000 carbon fibers with a diameter of 6 μm in one tree),
It has become clear that drift occurs.

<Experimental Example 3> The area of the electrode sensitive part of the carbon fiber electrode of this example, that is, the surface area of the oxygen sensitive part, was 1.413XIO-'cm.
The relationship between oxygen partial pressure concentration and current density when changing from 2 to 1.413 , 85 mmHg, and 128 mmHg), and the current density was measured. Table 3 shows the results.

If the relationship between oxygen gas partial pressure concentration and current density is plotted, the result will be as shown in FIG. The relationship between Po2 and density shows a good linear relationship. In particular, the electrode sensitive part (electrode area) is 2.826
At xlO-'am2, the current density increases by about 3 to 5 times compared to 1.43X10-'cm2, and the electric density increases from the order of 10-5 to 10-4.

As explained above, the surface area of the carbon fiber electrode (
That is, the surface area of the oxygen sensitive part) is 5°65xlO-'
It has become clear that drift occurs between cm2 and 8.478xlO-'am', and an oxygen sensor that has small drift and can accurately measure oxygen concentrations over a wide range of oxygen concentrations in a flow system or extracorporeal circulation system has been provided. Now you can.

Although this embodiment has described an oxygen sensor integrated with a reference electrode, the effects of this embodiment depend on the configuration of the oxygen electrode, and are not limited to this embodiment. Furthermore, it is clear that drift is also regulated by the surface area of the oxygen sensitive part in the other oxygen electrodes made of conductive substrates and porphyrin compounds described at the beginning of the Examples section.
The maximum value may be determined based on the technical idea of the present invention.

<Example 2> The oxygen sensor of this example is a minute oxygen sensor in which a carbon material including a carbon fiber material has a rod-shaped cross section of 10 cm2 or less, and is further directly coated with an oxygen gas responsive reduction membrane.

In this example, the area of the sensitive part is 1xlO""cm' or less (equivalent to between 3 and 4 pieces when the diameter of one carbon fiber tree is 6 μm), preferably 2.83X10-'Cm2 (equivalent to one piece of carbon fiber). be.

(Method for Manufacturing Carbon Fiber Electrodes) A glass tube with an outer diameter of 3 mm and a length of 5 cm was stretched using a micro-pole manufacturing device to manufacture two capillaries 71 having the shape shown in FIG. 7(a). Carbon fiber 72 (Besphite, manufactured by Toho Shiyon Co., Ltd.) is inserted into one capillary portion (stretched portion) of the capillary 71, and electron wax 73 (Sodenshi Co., Ltd.) is inserted as an insulating adhesive into the gap between the capillary and the capillary. (manufactured by Kogyo Co., Ltd.) for insulation. Mercury 74 was injected as a conductive adhesive from the other end, a lead wire 75 was inserted to establish continuity, and the end was sealed and fixed with an insulating adhesive 76 to prevent the mercury 74 from leaking.

Furthermore, the tip of the capillary tube was polished (0.5 μm abrasive paper PRI
-24: Manufactured by 3M Company) to complete carbon fiber' [i70]. A schematic diagram of the carbon fiber electrode 70 is shown in FIG. 7(b).

(Preparation of Micro Oxygen Sensor) The surface of the carbon fiber 72 of the carbon fiber electrode 70 was coated with meso-tetra(0-aminophenyl)cobalt porphyrin (Co-TAPP) by the method shown below.
It was coated with an electropolymerized membrane 77 of (abbreviated as ).

The electropolymerized film 77 covers the carbon fiber 'rfj, the pole 7
Using a three-electrode cell with 0 as the working electrode, a commercially available A g /A g CIl electrode as the reference electrode, and a platinum winding as the counter electrode, +1. sv (vs, Ag/AgCf
The deposition was completed by electrolyzing for 60 seconds at the constant potential of 1).

Electrolyte composition 1 mM Co-TAPPo, 1
M NaCJZO4 Solvent Acetonitrile The current change in constant potential electrolysis at this time is shown in Figure 8, and the time to converge to a constant current is approximately 60 seconds.For comparison, two carbon fibers (cross-sectional area 5.652X10-'cm2)
In the case of 0 seconds and 5 lines (cross-sectional area: 1.413 x 10-6 cm2), the current value becomes constant in 20 seconds, a thin film is formed in this order, and the film control time becomes shorter.

A schematic diagram of the oxygen sensor manufactured in this way is shown in Figure 7 (C
).

Experimental Example 4> Using an electrode cell using the fine carbon fiber electrode shown in FIG. 7(b) of Example 2 as a working electrode, a saturated sodium chloride calomel electrode as a reference electrode, and a platinum mesh as a counter electrode, the following electrolyte was used. 20mM Fa(CN)a′-0, 1M NaCfLO4 in Fe(CN)6”- and Fe(CN) on the oxygen electrode surface.
A cyclic portagram of the redox reaction of a'- was measured.

The results are shown in FIG. 9(a). At the same time, the cross-sectional area of carbon fiber is 1.413xlO-'cm2 (bundle of 5),
Figure 9 (b
) and (C).

As a result, the oxygen reduction current value becomes almost constant in Figure 9(a), but the cross-sectional area of the carbon fiber is 1.413x.
lO””am2 (more than 5 bundles of carbon fiber),
It was confirmed that the oxygen reduction current value changed as the potential value changed.

Therefore, if a constant current value is to be obtained, the area of the carbon electrode is approximately 10-'cm2 or less, preferably 2.83 x 10-'am' (equivalent to one carbon fiber).

Experimental Example 5> Using the oxygen sensor created in Example 2, the area of the electrode sensitive part was set to 2.826X10''cm2 to 2.826X10
-'cm' current density (A-7cm)
The relationship between the oxygen partial pressure (mmHg) and the oxygen partial pressure (mmHg) is shown in Table 4 and Figure 10, which plots this relationship. 1
The measurement was performed in place of 28 mmHg. This current density and 902
When the residual current is determined from the relationship of the partial voltages, the results are as shown in the residual current column of Table 4.

1 or less margin 1 As a result, the area of the electrode sensitive part is 8.478X10-'c
m' (5 bundles) or less, the residual current is 1.48
4xlO-5A/cm" ~ 1.770x10""A
/Cm''.

Experimental Example 6> Similar to Experimental Example 5, using the oxygen sensor of Example 2, the temperature was raised to 37°C with an electrolyte solution (phosphate buffer solution pH 7.4).
Drift (variation in current density) on the electrode due to the influence of flow was investigated under conditions of a constant oxygen concentration of 140 mmHg adjusted to ±0.05°C. By changing the stirring speed of the stirrer that stirs the test solution, the flow rate was set to 250 ml and 111 minutes and 1200 ml! The first result is the result when the time is changed to /min.
Shown in Figure 1.

Electrode area is 2.826X10-'cm22.826xl
O-'am28.478x10-6cm2, 2.826
As X10-'am' becomes larger, the drift tends to become larger. Therefore, the electrode area is 2.8
26X10””cm2 (1 carbon fiber) ~2.
826X10-6cm2 (10 carbon fibers)
Among them, preferably 2.826xlO-'cm2 (one carbon fiber) is considered to be good for wood purposes since it has a small drift.

In this way, the oxygen sensor of this example shows (i) the electrochemical behavior of Fe (CN) 63-"- of the carbon electrode (
Redox reaction response) is the area of the electrode sensitive part 1010-6
a, preferably 2.83 x 10-'cm', the redox waves are symmetrical and the current value on the electrode surface is almost constant.

(if) As a result of using a membrane-coated oxygen electrode in which an oxygen gas responsive reduction membrane was directly coated on this carbon electrode base,
Drift is hardly visible.

(iii) The residual current value calculated from the oxygen partial pressure versus current density increases as the carbon pole base area becomes smaller, but the residual current I
It is constant on the order of 10-' (A/cm2).

(iv) Carbon 1! Membrane coating electrolytic conditions when coating an oxygen gas responsive reduction membrane on top, for example, electrolytic reaction time control is limited to extremely short control within 10 seconds when the area of the electrode sensitive part is 10'''cm2 or more. However, 10-8 cm
If it is 2 or less, electrolytic membrane coating control can be performed for a long time (1 minute or more) of 60 seconds or more.

[Effects of the Invention] According to the present invention, it is possible to provide an oxygen sensor that has small drift and can measure a wide range of oxygen concentrations when used in a flow system or an extracorporeal circulation system.

Further, it is possible to provide a minute oxygen sensor with a uniform surface, easy to control film coating, and less drift.

More specifically, (i) the electrochemical behavior (redox reaction response) of Fe (CN) 63-74- of the carbon electrode is determined when the area of the electrode sensitive area is 10"" am2 or less, preferably 2.83 x 10-
'cm2, the redox waves are symmetrical and the current value on the electrode surface is almost constant.

(ii) As a result of using a membrane-coated oxygen electrode in which an oxygen gas-responsive reduction membrane was directly coated on this carbon electrode base,
Drift is hardly visible.

(iii) The residual current value calculated from the oxygen partial pressure versus current density increases as the base area of the carbon utility pole becomes smaller, but if the cross-sectional area is less than Xl0-5 cm2, the residual current value is 1 x
It is on the order of 10-' (A/cm2).

(iv) Membrane coating electrolysis conditions when coating an oxygen gas responsive reduction membrane on a carbon electrode, for example, electrolytic reaction time control is extremely short, within 10 seconds when the area of the electrode sensitive part is 1010-6a or more. is limited to the control of 10-”am2
If it is below, it is possible to control the electrolytic membrane coating for a long time of 60 seconds or more (1 minute or more).

[Brief explanation of the drawing]

Figure 1 (a) is a schematic diagram of the oxygen sensor manufactured in this example, Figure 1 (b) is an enlarged cross-sectional view showing the oxygen electrode of this example, and Figure 2 is a schematic diagram of the oxygen sensor manufactured in this example. Figure 3 is a diagram showing the oxygen sensor measurement circuit; Figure 3 is a diagram of the oxygen measurement system for the circulatory system of an artificial lung device; Figure 4 is a diagram showing current density versus flow rate; Figure 5 is a diagram showing current density versus elapsed time. Figure 6 is a diagram showing the current density versus oxygen partial pressure, Figure 7 (a) is a diagram showing the glass capillary of this example, and Figure 7 (b) is a diagram showing the structure of the carbon fiber electrode of this example. , FIG. 7(C) is a diagram showing the structure of the oxygen sensor of this example, FIG. 8 is a diagram showing current changes in constant potential electrolysis during the production of an electrolytically polymerized membrane, and FIGS. 9(a) to (C) Figure 10 shows the cyclic portamogram of the redox reaction of the micro carbon fiber electrode of this example. Figure 10 shows the current density and the oxygen FIG. 11 is a diagram plotting the relationship with partial pressure. FIG. 11 is a diagram showing the drift on the electrode due to the influence of flow in the oxygen sensor of this example. In the figure, 1... BPG, 2... Conductive adhesive, 3...
・Lead wire, 4'...Epoxy adhesive 4.5...
Teflon tube, 6... Meso-tetra(O-aminophenyl) cobalt porphyrin electrolytic polymer membrane, 7...
Silver wire, 8... Polyvinyl alcohol aqueous solution, 9...
Silicone tube, 10...Thermo plug, 19.
・・Urethane adhesive, 20・・Oxygen sensor, 70・
... Carbon fiber electrode, 71 ... Glass capillary, 72 ... Carbon fiber, 73 ... Insulating adhesive, 74 ... Conductive adhesive, 75 ... Lead wire,
76... Insulating adhesive, 77... Electropolymerized membrane. ■ 0) IO Intercostal ('7T) Figure 5 PO2 (mmHg)

Claims (1)

[Scope of Claims] (1) An oxygen sensor comprising an electrically conductive substrate and an oxygen sensitive portion made of a porphyrin derivative compound and/or a metal complex compound thereof covering the electrically conductive substrate, the surface area of the oxygen sensitive portion being An oxygen sensor characterized in that the size of the sensor is such that the drift is equal to or less than a predetermined value. (2) The oxygen sensor according to claim 1, characterized in that the drift is 5×10^-^5 A/cm^2 or less. (3) The surface area of the oxygen sensitive part is at most 8.5 x 10
The oxygen sensor according to claim 1, characterized in that the diameter is ^-^4 cm^2. (4) The oxygen sensor according to claim 1, wherein the conductive substrate is made of conductive carbon. (5) The oxygen sensor according to claim 4, wherein the cross-sectional area of the carbon material is 10^-^6 cm^2 or less. (6) The oxygen sensor according to claim 1, wherein the porphyrin derivative is a meso-phenyl derivative. (7) The metals forming the porphyrin complex are Fe, C
7. The oxygen sensor according to claim 6, wherein the oxygen sensor is made of Ni. (8) The oxygen sensor according to claim 1, wherein the porphyrin compound is selected from a porphyrin compound substituted with a hydroxy aromatic semiconductor at the meso position and a porphyrin compound substituted with an amino aromatic semiconductor device at the meso position. (9) The metal complex of the porphyrin compound is selected from a metal complex of a porphyrin having a hydroxy aromatic semiconductor device at the meso position and a metal complex of a porphyrin having an amino aromatic semiconductor device at the meso position. 1
Oxygen sensor as described in section.