JP2000346807A - Reference electrode for electrochemiluminescence detector - Google Patents

Abstract

(57) [Summary] [Issue] An ion selective electrode that generates a stable potential for a long time,
An inexpensive reference electrode used as a reference potential reference for a potential measurement type chemical sensor such as an enzyme electrode and a detector for an immunoanalyzer utilizing electrochemiluminescence. A porous ceramic having a water absorption of 6 to 14% is fixed to a liquid junction, a housing is made of a plastic material having no light transmission, an internal electrode is a silver / silver chloride electrode, and the internal liquid is supersaturated. Reference electrode for an electrochemiluminescence detector composed of potassium chloride solution and silver chloride powder. Reference potentials for chemical sensors such as ion selection electrodes and enzyme electrodes, and detectors for immunoanalyzers using electrochemiluminescence, which can be used for at least twice as long as conventional comparison electrodes without cost increase. A suitable reference electrode can be provided at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a potential measurement type chemical sensor for quantitatively analyzing various components contained in body fluids such as blood and urine, which is mainly used in the field of medical clinical examinations. The present invention relates to a detector for an immunoanalyzer using electrochemiluminescence and a comparison electrode used as a reference potential for voltammetry measurement by a three-electrode method performed in a basic field of electrochemistry.

[0002]

2. Description of the Related Art In a chemical sensor for quantitatively analyzing various chemical components such as ions contained in a solution, in order to perform more accurate measurement, a reference electrode which always generates a constant potential in principle is used as a pair. is necessary. In addition to the detector for an immunoanalyzer using electrochemiluminescence, in voltammetry measurement using a three-electrode method, it is most important that the potential of the working electrode is set similarly, and this potential is a reference. A reference electrode is required. From such demands, various comparative electrodes have been proposed as shown in the electrochemical measurement method (above) (published by Gihodo) p89 to p101.

[0003]

Here, in addition to a potential measurement type chemical sensor and a detector for an immunoanalyzer using electrochemiluminescence, it is ideal as a reference electrode for reference potential reference in voltammetry measurement by a three-electrode system. Considering what is important, it is important to have the following properties. That is: 1) The electrode reaction on the internal electrode surface is reversible and Nernst response with a certain chemical species in the internal liquid.

2) The potential is stable with respect to time during storage and during use.

3) The potential immediately returns to the initial potential even when a minute current flows.

4) When the internal electrode is a silver / silver chloride electrode, the solid layer must be stable without being dissolved in the internal liquid for a longer time.

However, of these items, the problem to be solved by the present invention mainly relates to the items 2) to 4), namely, the short-term and long-term stability of the reference electrode.

[0008] In the analyzer for clinical tests to which the present invention is mainly used, not only is it required to measure more reliably for each measurement item, but also to respond to unexpected measurements such as urgent sample measurement requests. It is desirable to reduce the downtime of the apparatus due to parts replacement or the like as much as possible so as not to reduce the operation rate.

For this reason, in the case of a chemical sensor or a detector using electrochemiluminescence conventionally used in clinical biochemistry and immunoanalyzers for clinical use, not only the main body but also the reference electrode has a long life and is inexpensive. There has been a demand for the development of unnecessary components such as maintenance.

[0010]

Means for Solving the Problems To solve such problems, the present invention uses the following means. That is, 1) embedding a porous ceramic into the liquid junction provided at the tip of the comparative electrode housing in order to connect the flow path with the target chemical sensor or detector and secure electrical conduction with the internal liquid. And the water absorption, which is an index indicating the porosity of the ceramic, is 6 to 14%.

2) The reference electrode housing is made of a material having a light-shielding property or a plastic mixed with a dye such as black for the purpose of securing the light-shielding property.

3) A porous ceramic is buried in the liquid junction at the tip of the comparative electrode housing, and an O-ring made of rubber is buried around the same. A structure for mounting a liquid leakage prevention component so as to cover the end face of the front end of the embedded comparative electrode housing.

4) The internal electrode is a silver / silver chloride electrode, and the internal liquid is composed of a saturated potassium chloride solution and silver chloride powder.

Here, the operation of each of the above means will be described.

In the means 1), the liquid junction is made of porous ceramic, and the water absorption, which is an index indicating the porosity of the ceramic, is 6 to 14%. Glass, platinum, cellophane, and the like can be considered as a material for forming the liquid junction. Compared to these, porous ceramic has an advantage that it is inexpensive and easy to handle. In addition, the water absorption is 6-14%
The reason for this is that the liquid inside the electrode flows out slightly from the end face of the liquid junction to ensure electrical continuity between the flow path between the internal electrode and the target detector, etc., and the physical and chemical This is to maintain a stable environment for a long period of time and secure a stable potential. Here, when the water absorption is 6% or less, the porous ceramic becomes excessively dense, and the resistance between the inside and outside of the comparative electrode sandwiching the liquid junction increases to 100 kΩ or more. As a result, a special and expensive electric circuit is required to take out a stable electrode potential without being affected by electric noise or the like generated from the main body of the analyzer. Further, the liquid junction is easily clogged by crystallized potassium chloride or the like, and it is difficult to stably secure electric conduction to be maintained between the flow path of the target detector or the like and the liquid inside the electrode for a long time. . When the water absorption is set to 14% or more, an excessive amount of the liquid inside the electrode, which should be discharged from the end face of the liquid junction part, flows out excessively, destabilizing the physical and chemical environment around the liquid junction part and making the electrode more stable. The internal fluid is rapidly lost, resulting in an unusable state before the specified reference electrode life is met.

In the means 2), the comparative electrode housing is made of a material having a light shielding property or a plastic mixed with a dye such as black for the purpose of securing the light shielding property. Generally, a silver / silver chloride electrode serving as an internal electrode is deteriorated by ultraviolet rays and cannot maintain a constant potential. In order to prevent this phenomenon as much as possible, it is necessary to make the comparative electrode housing made of a light-shielding material so that ultraviolet rays do not directly hit the silver / silver chloride electrode.

Means 3) employs a structure in which a rubber O-ring is buried around a liquid junction made of porous ceramic buried at the tip of the reference electrode housing. This makes it possible to easily secure airtightness that should be maintained between the reference electrode and the flow path of the target detector when using the reference electrode, thereby improving the stability of the physical and chemical environment around the liquid junction. Can be maintained for a long time. Also, a structure is adopted in which a component for preventing liquid leakage is mounted so as to cover the end face of the front end of the comparative electrode housing in which the porous ceramic and the O-ring are embedded when the comparative electrode is stored. This prevents the potassium chloride solution in the electrode internal liquid from flowing out and crystallizing from the tip of the liquid junction to render the comparative electrode inoperable, and also to prevent the internal liquid from flowing out of the comparative electrode or the evaporation of water as much as possible. Thus, a stable comparison electrode with less potential fluctuation due to a change in the internal liquid concentration can be provided at low cost.

In the means 4), the internal electrode is a silver / silver chloride electrode, and the internal liquid of the electrode is composed of a supersaturated potassium chloride solution and silver chloride powder. The silver / silver chloride electrode is inexpensive and its generated potential is relatively stable as long as it is not exposed to ultraviolet light. However, if the internal liquid concentration around the electrode changes, its potential is logarithmically proportional to the concentration according to the Nernst equation. Change. Therefore, in order to maintain a stable potential for a long period of time, the concentration of the internal liquid must be kept constant. Here, when the reference electrode is used on a clinical biochemistry or immunoanalyzer, as the number of measurements increases, the concentration of potassium chloride in the electrode internal solution flows out due to the concentration gradient with the solution to be measured, and the concentration decreases. Phenomenon was seen. Measure 4)
In the above, a supersaturated potassium chloride solution was sealed in advance as the electrode internal solution. The potential cannot be secured. Therefore, silver chloride powder was added in advance, and the dissolution of silver chloride in the electrode internal solution was minimized based on the principle of solubility equilibrium.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a cross-sectional structure of a comparative electrode developed for use as a detector of an analyzer for measuring minute components in blood using an immunoreaction and electrochemiluminescence. The comparison electrode in FIG. 1 is screwed into and fixed to the flow path of the target electrochemiluminescence detector by means of a screw cut around the liquid junction. The comparative electrode housing 1 is made of black ABS resin to prevent transmission of ultraviolet rays, and an alumina porous ceramic 3 having a water absorption of about 10% is fixed to a liquid junction 2 at the tip of the housing 1. On the other hand, the internal electrode 5 is 1 mm in diameter and 15 mm in length.
The electrode internal liquid 4 is composed of 2. silver / silver chloride electrode.
0.02 g of supersaturated potassium chloride solution
Silver chloride powder is added. One end of the internal electrode 4 is connected via a connector to an electric circuit including a potentiostat and the like. This electric circuit is similarly connected with a working electrode made of platinum, which is installed on the target detector body, and its counter electrode.
Electrodes constitute an electrochemical light emitting circuit.

Here, the sample to which the luminescent label such as a ruthenium complex which is guided in a predetermined sequence on the working electrode in the detector and is temporarily retained by a magnetic force or the like is preliminarily bound is used. When a constant voltage is applied by using, the sample emits light of a constant wavelength proportional to its concentration. The amount of this light is detected using a photomultiplier tube or the like, and is compared with a calibration curve prepared using a sample whose concentration is known in advance, thereby calculating the concentration of the sample whose concentration is unknown.

FIG. 2 is a sectional view showing a state in which a threaded cap 6 is mounted as a component for preventing internal liquid evaporation so as to cover the liquid junction 2 at the tip of the comparative electrode housing 1 during storage of the comparative electrode. In the figure, the liquid junction 2 at the tip of the comparative electrode housing 1 has a rubber O
The ring 3 is embedded so that the threaded cap 6 is slightly in contact with the end face of the inner surface of the threaded cap 6 when the threaded cap 6 is screwed and fixed to the reference electrode housing 1 by a screw cut around the liquid junction 2. Has become. This makes the reference electrode inoperable due to outflow or crystallization of the potassium chloride solution in the electrode internal liquid from the liquid junction tip, or changes in the internal liquid concentration due to evaporation of water in the internal liquid and the resulting potential. Fluctuations can be minimized and storage at room temperature for at least one year is possible.

FIG. 3 shows the results of a comparative test of the electromotive force stability during use performed using the conventional comparative electrode and the comparative electrode according to the present invention. In the figure, the horizontal axis indicates the number of measurements applied to the electrochemical luminescence detector using the comparative electrode, and the vertical axis indicates the electromotive force of the comparative electrode at that time. The graph 8 shows the results of the service life test of the conventional comparative electrode, and the graph 9 shows the results of the service life test of the improved comparative electrode according to the present invention.

In this test, the comparative electrode used was changed only in the internal liquid composition of the electrode, and the other components were the same. That is, the comparative electrode housing 1 was made of plastic made of black ABS resin, and the porous ceramic 3 made of alumina having a water absorption of about 10% was fixed to the liquid junction 2 at the tip of the housing 1. For the electrode internal solution 4, the conventional comparative electrode used only 2.0 ml of a saturated potassium chloride solution, while the improved comparative electrode according to the present invention added 2.0 ml of a supersaturated potassium chloride solution to 2.0 ml of a supersaturated potassium chloride solution. Silver chloride powder was added. The internal electrode 5 is silver /
A silver chloride electrode was used. As is clear from the figure, in the comparative electrode according to the present invention, the electromotive force of the internal electrode 5 after 50,000 measurements hardly changed, whereas when the conventional comparative electrode was used, the load was The electromotive force gradually rises after the start, and the specification that the change in the electromotive force of the internal electrode 5 after 50,000 measurements must be less than ± 10 mV with respect to the initial value is 20,000.
It can be seen that the specification is not satisfied at +10 mV or more after the first measurement. From the above, it is determined that the comparative electrode according to the present invention can be used stably for at least twice as long as the conventional comparative electrode.

FIG. 4 shows the results of a comparison experiment of the comparative electrode life (in use and in storage) when the water absorption of the porous alumina ceramic 3 fixed to the liquid junction 2 is changed. The term "life" as used herein means that the change in the electromotive force of the internal electrode after the 50,000 measurements shown above is ± 10 mV from the initial value.
It must be less than or equal to (at the time of use) Even if it starts using after storing at room temperature for one year, it must operate normally and the change of the electromotive force of the internal electrode must be ± 10 mV or less from the initial (at the time of storage) Based on the specifications, the number of measurements when the specifications were no longer satisfied (when used) or the number of months when the specifications were not satisfied (during storage) was determined.

In the figure, reference numeral 11 denotes a service life test result,
Numeral 10 indicates the test result of the shelf life. In the comparative electrode used here, the comparative electrode housing 1 is a plastic made of black ABS resin, and a liquid junction 2 provided at the tip of the housing 1 is made of an alumina porous ceramic 3 having a water absorption of about 10%. It is fixed. The electrode internal solution 4 is obtained by adding 0.02 g of silver chloride powder to 2.0 ml of a saturated potassium chloride solution. In this case, as can be seen from the figure, the service life is almost constant (around 75,000 times) when the water absorption of the porous ceramics 3 made of alumina is 14% or less. When a porous ceramic having a too low water absorption rate is used for the liquid junction 2, the resistance between the inside and outside of the comparison electrode sandwiching the liquid junction 2 becomes as high as 100 kΩ or more, and the electric noise and the like generated from the main body of the analyzer become large. It is liable to be affected, and a special electric circuit is required to extract a stable electromotive force from the reference electrode, resulting in an expensive device. In addition, when the water absorption rate is 6% or less, a liquid junction is generated during storage of the reference electrode. Since it is easy to be clogged and it is difficult to secure electrical continuity, as a result, only a storage life of about 6 months can be ensured. When used for the detector of an epidemiological analyzer, the water absorption of the porous ceramic should be 6-14.
% Is desirable.

Further, in the comparative electrode, the potassium chloride solution in the internal liquid of the electrode at the time of storage flows out from the tip of the liquid junction 2 and crystallizes to render the comparative electrode inoperable, or the electrode due to evaporation of water in the internal liquid 4. In order to prevent the change of the internal liquid concentration as much as possible, a screw cap 6 is provided so as to cover the tip of the liquid junction 2. When the reference electrode is stored, when the threaded cap 6 is tightened, the tip of the liquid junction 2 is sealed by interaction with the rubber O-ring 7 embedded around the liquid junction 2 at the tip of the reference electrode housing 1. At least, a stable electromotive force was obtained within the specifications even after storage at room temperature for one year or more.

[0028]

Industrial Applicability A chemical sensor such as an ion selection electrode and an enzyme electrode which can be used stably for at least twice as long as a conventional comparative electrode without increasing the cost, and a detector for an immunoanalyzer utilizing electrochemiluminescence. Thus, it is possible to easily provide a reference electrode suitable for reference potential reference.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the internal structure of a comparative electrode according to the present invention.

FIG. 2 is a cross-sectional view showing a state where components for preventing liquid leakage during storage of a comparative electrode according to the present invention are mounted.

FIG. 3 is a graph showing the results of a service life test performed using a comparative electrode according to the present invention and a conventional comparative electrode.

FIG. 4 is a graph showing use and storage life test results when the water absorption of a porous ceramic is changed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reference electrode housing, 2 ... Liquid junction part, 3 ... Porous ceramic, 4 ... Electrode internal liquid, 5 ... Internal electrode, 6 ... Liquid leakage prevention parts (screw cap), 7 ... O-ring, 8 ... Graph showing the service life test result when using the comparative electrode of the conventional product, 9 ... Graph showing the service life test result when using the comparative electrode according to the present invention, 10 ... Various porous ceramics having different water absorption rates Is a graph showing the results of a storage life test when using various ceramics having different water absorption rates.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 27/42 311 G01N 33/483 F 33/483 C 33/543 575 33/543 575 27/30 313A / / A61B 5/145 A61B 5/14 310

Claims (4)

[Claims] In a comparative electrode used as a reference potential reference for an immunoassay detector using electrochemiluminescence, a comparative electrode housing is formed of plastic, and an electrode internal liquid filled therein is used. Mainly composed of potassium chloride solution, has a silver / silver chloride electrode for generating a reference potential in a form immersed in the electrode internal liquid, and connects the flow paths of the target detectors etc. to ensure electrical conduction Wherein the liquid junction provided at the tip of the comparative electrode housing is formed by embedding a porous ceramic, and the ceramic has a water absorption of 6 to 14%, which is an index indicating the porosity. Reference electrode for chemiluminescence detector. 2. The comparison electrode according to claim 1, wherein the plastic forming the comparison electrode housing has a light-shielding property or is mixed with a dye capable of securing the light-shielding property. Reference electrode for electrochemiluminescence detector. 3. A comparative electrode according to claim 1, wherein an O-ring made of rubber is embedded around a liquid junction made of porous ceramic embedded at the tip of said comparative electrode housing. A comparative electrode for an electrochemiluminescence detector, wherein a component for preventing liquid leakage is mounted so as to cover an end face of a front end of the comparative electrode housing in which the porous ceramic and the O-ring are embedded. 4. A comparison electrode for an electrochemiluminescence detector according to claim 1, wherein the liquid inside the electrode of the comparison electrode is composed of a supersaturated potassium chloride solution and silver chloride powder.