JP2009156670A - Comparison electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a comparison electrode constituted, with the evaporation of moisture from an internal liquid being suppressed. <P>SOLUTION: The comparison electrode is equipped with a support pipe provided with a liquid communication part; the internal liquid charged in the support pipe; the internal electrode immersed in the internal liquid; the liquid communication part for electrically connecting the internal liquid and a sample solution; and the movable plug placed on the liquid surface of the internal liquid to move through the support pipe so as to follow the movement of the liquid surface and constituted of fine particles. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a comparative electrode in which water evaporation from an internal liquid is suppressed.

  Conventionally, the ion concentration is measured by bringing the sensitive membrane of the ion selective electrode into contact with the sample solution and measuring the potential difference according to the ion activity generated at the interface between the sensitive membrane and the sample solution. Therefore, a reference electrode that can present a constant reference potential is required in addition to the ion selective electrode.

  For example, the reference electrode is formed by immersing an electrode made of silver / silver chloride or mercury / mercury chloride in an internal solution made of a KCl solution having a high concentration (3.3 mol / L to saturation). It is configured to come into contact with the sample solution through a liquid junction made of a porous material such as glass.

  The internal liquid and the internal electrode are accommodated in a support tube made of an electrical insulating material and sealed in the support tube by a lid, and the liquid junction is provided in an opening formed in the support tube. Yes.

  In such a comparative electrode, when the temperature of the sample solution is high, the temperature of the comparative electrode also rises during measurement, the air between the lid and the internal liquid expands, and the water in the internal liquid evaporates. When water vapor is generated, pressure is applied to the internal liquid, and the internal liquid may be pushed out from the liquid junction and leaked excessively into the sample solution.

  In addition, when the measurement is finished and the temperature of the reference electrode is lowered, the air between the lid and the internal liquid contracts, and the water vapor is liquefied, so that the inside of the support tube is in a negative pressure state, and from the liquid junction Air or sample solution may enter the support tube. For this reason, as the temperature of the reference electrode fluctuates, the composition of the internal liquid fluctuates to increase the liquid-liquid potential, or bubbles are formed in the liquid junction or internal liquid, and the sample solution and internal liquid, or The electrical connection between the internal liquid and the internal electrode may deteriorate, resulting in a measurement error.

For this reason, a pressure adjustment layer made of a highly adhesive silicone gel is provided on the liquid surface of the internal liquid to adjust the pressure in the support tube of the internal electrode (Patent Document 1).
JP-A-2005-77252

  However, since the silicone gel has a high adhesive force to the inner wall of the support tube, it does not follow even if the liquid level of the internal liquid moves, and moisture evaporates from the internal liquid, causing a gas layer between the silicone gel and the internal liquid. If possible, the gas layer expands or contracts as the temperature changes, so that the internal liquid may flow out excessively from the liquid junction, or air or sample solution may enter the internal liquid. Along with this, the inter-liquid potential may increase or the measurement itself may become impossible.

  In addition, since the silicone gel cannot prevent water evaporation from the internal liquid, the liquid-potential increases or measurement error occurs even when the composition of the internal liquid changes due to water evaporation.

  In particular, these phenomena may cause various problems in the reference electrode in which the internal liquid is a gel-like material, and a liquid layer is formed in the internal liquid due to the penetration of the sample solution, or the internal liquid is dried and cracked. Intrusion of air may cause bubbles in the internal liquid, increasing the liquid-liquid potential or making the measurement itself impossible.

  Therefore, the present invention is intended to provide a comparative electrode in which moisture evaporation from the internal liquid is suppressed.

  That is, the comparative electrode according to the present invention includes a support tube provided with a liquid junction, an internal liquid filled in the support tube, an internal electrode immersed in the internal liquid, and the internal liquid and the sample solution. A liquid junction part for electrical connection; and a movable stopper made of fine particles placed on the liquid level of the internal liquid and movable in the support tube following the movement of the liquid level; It is characterized by providing.

  If this is the case, a movable plug that can move in the support tube following the movement is placed on the liquid surface of the internal liquid, so that the air in the support tube is in contact with the internal liquid. Since the area is reduced, water evaporation from the internal liquid is suppressed, and fluctuations in the composition of the internal liquid can be prevented.

  In addition, since the movable stopper is composed of fine particles, even if moisture evaporates from the internal liquid, water vapor is released into the support tube from the gap between the fine particles, and there is an air layer between the internal liquid and the movable stopper. Never formed. For this reason, as in the case of the conventional comparative electrode, the gas layer formed between the silicone gel and the internal liquid expands and contracts as the temperature changes, so that the internal liquid flows out excessively from the liquid junction, Air or sample solution does not enter the internal liquid through the section.

  Further, in the case where the support pipe is provided with a ventilation part, when the movable stopper moves downward following the liquid level of the internal liquid, air flows into the upper part of the movable stopper from the ventilation part. The pressure of the upper air layer and the pressure of the internal liquid can always be balanced. For this reason, the internal liquid outflow from the liquid junction becomes smooth, and the fluctuation of the liquid junction potential can be reduced.

  The fine particles preferably have a particle size of 0.05 to 3 mm.

  The voids of the fine particles may be filled with a hydrophilic polymer, oil, or grease.

  The present invention is particularly effective when the internal liquid is a gel-like body.

  An ion selective electrode provided with the comparative electrode according to the present invention is also one aspect of the present invention.

  Thus, according to the present invention, fluctuations in the composition of the internal liquid due to moisture evaporation are suppressed, and the internal liquid flows out excessively from the liquid junction, or air or sample solution enters the internal liquid via the liquid junction. Therefore, it is possible to obtain a comparative electrode that is excellent in measurement accuracy and stable over a long period of time.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the electrode 10 according to the present embodiment is a composite electrode type in which a comparison electrode unit 1 and a pH electrode unit 2 are integrated, and a support tube 3 having an interior partitioned into two. Is provided.

  The support tube 3 has a tapered bottomed cylindrical shape as a whole, a tip portion is formed in a sharp shape, and an open portion is formed in a base end portion. Since the support tube 3 is formed with a sharp tip, not only is the electrode 10 immersed in a liquid sample solution to measure its pH, but the electrode 10 is pierced into a solid measurement object, It is also possible to measure the pH. Such a support tube 3 is formed of a material having sufficient electrical insulation as well as elasticity such as synthetic resin so that it is not easily damaged even when it is stabbed into a solid measurement object.

  One side of the support tube 3 is a reference electrode support tube 3a, and the other side is a pH electrode support tube 3b.

  As shown in FIG. 1, the comparative electrode unit 1 includes a comparative electrode support tube 3a, an internal liquid 7 filled in the comparative electrode support tube 3a, and an internal part made of, for example, silver / silver chloride immersed in the internal liquid 7. Electrode 6, movable stopper 8 placed on the surface of internal liquid 7, liquid junction 4 provided in the vicinity of proton sensitive portion 11 of comparison electrode support tube 3a, and proximal end of comparison electrode support tube 3a The ventilation part 5 provided in the part.

  As the internal liquid 7, for example, an AgCl supersaturated 3.3M KCl aqueous solution was gelled by a hydrophilic polymer such as carboxymethyl cellulose (hereinafter referred to as CMC), agar, gelatin, glue, alginic acid, an acrylic water-absorbing polymer, or the like. A gel-like body is used. Since these hydrophilic polymers also have a water retention effect, the internal liquid 7 configured in this way is not easily dried. Furthermore, a moisture evaporation inhibitor such as glycerin or ethylene glycol may be added to the internal liquid 7 so that the internal liquid 7 can be retained more effectively.

  The movable plug 8 is composed of fine particles 81, and can move in the comparison electrode support tube 3a while following the movement of the liquid level of the internal liquid 7 well. Examples of the fine particles 81 include those made of inorganic compounds such as ceramic, alumina, and zirconia, and synthetic resins such as polystyrene, polyethylene, and polypropylene.

  The particle size of the fine particles 81 is preferably about 0.05 to 3 mm, more preferably about 0.1 to 2 mm. If the particle size is less than 0.05 mm, it is too small to form a suitable space for water vapor to be released between the fine particles 81, and there is a risk that water vapor may accumulate between the movable plug 8 and the internal liquid 7. In addition, the ventilation part 5 may be clogged. When the particle diameter exceeds 3 mm, the particle size is too large, the contact area between the liquid surface of the internal liquid 7 and the fine particles 81 is small, and moisture evaporation from the internal liquid 7 may not be effectively prevented.

  Further, since the fine particles 81 are placed on the liquid surface of the internal liquid 7, it is necessary that the specific gravity is smaller than that of the internal liquid 7. The shape of the fine particles 81 is not particularly limited, and examples thereof include a sphere, a columnar body, and a disk-shaped body.

  The voids between the fine particles 81 may be filled with a hydrophilic polymer such as an acrylic water-absorbing polymer such as CMC, agar, gelatin, glue, alginic acid, acrylamide and the like. When these hydrophilic polymers are filled in the voids of the fine particles 81, drying of the internal liquid 7 is suppressed due to the water retention effect of the hydrophilic polymer, and the hydrophilic polymer functions as a lubricant. Can follow the movement of the liquid surface of the internal liquid 7 and move more smoothly in the reference electrode support tube 3a. Further, oil or grease may be filled in the voids of the fine particles 81 instead of the hydrophilic polymer.

  The liquid junction part 4 is formed by filling an opening formed in the vicinity of the proton sensitive part 11 of the reference electrode support tube 3a with a rod-like porous body made of polyethylene or the like to which hydrophilicity is imparted. If the porous body is made of polyethylene having been subjected to hydrophilic treatment, the internal liquid 7 can easily enter the porous body and come into contact with the sample solution. Connection can be made reliably.

  The ventilation portion 5 is formed by filling a porous body made of polyethylene or the like into an opening formed at the base end portion of the comparison electrode support tube 3a, and is located above the movable plug 8 via the porous body. The air layer 9 and the outside air can be circulated. When the porous body is made of polyethylene having a hydrophobic property, it is possible to prevent the sample solution from entering the comparison electrode support tube 3a through the vent portion 5 when the electrode 10 is immersed in the sample solution. . The porous body may be subjected to water repellent treatment so that the porous body has stronger hydrophobicity.

  As shown in FIG. 1, the pH electrode unit 2 includes a pH electrode support tube 3b and a proton sensitive unit 11 provided at the lower end of the pH electrode support tube 3b.

  The proton sensitive part 11 is composed of an ISFET (Ion Sensitive Field Effect Transistor) exposed from an opening formed at the tip of the pH electrode support tube 3b. The ISFET is formed on the substrate 111, and the substrate 111 is accommodated in the pH electrode support tube 3b so that the ISFET is exposed from the opening formed at the tip of the pH electrode support tube 3b.

  As shown in FIG. 2, the electrode 10 according to the present embodiment is configured to be detachably attached to the probe main body 13 using a screwing member 12, and the probe 20 including the probe main body 13 and the electrode 10. Is configured to be detachable from the ion concentration meter main body 30 by a signal cable 14. The probe 20 is connected to the ion concentration meter main body 30 to constitute the ion concentration meter 100, and is used for pH measurement.

  When using such a composite electrode type electrode 10 to measure the pH of the sample solution, the electrode 10 is attached to the probe body 13 and the operator immerses the tip of the electrode 10 in the sample solution. Since the 4 and the proton sensitive part 11 are in contact with the sample solution at positions close to each other, the pH can be measured.

  According to the electrode 10 according to the present embodiment configured as described above, the liquid surface of the internal liquid 7 of the comparison electrode unit 1 is always covered with the movable stopper 8, so that the internal liquid 7 and the comparison electrode support tube 3a The contact area with air is reduced, and even when the sample solution is at a high temperature of about 60 ° C., the evaporation of moisture from the internal liquid 7 is suppressed. For this reason, since the fluctuation | variation of the composition of the internal liquid 7 is suppressed, a measurement error can be prevented.

  Further, since the movable stopper 8 is composed of the fine particles 81, even if moisture is evaporated from the internal liquid 7, the water vapor is released into the reference electrode support tube 3 a from the gap between the fine particles 81. There is no air layer between the movable stopper 8. For this reason, as in the conventional comparative electrode, the gas layer formed between the silicone gel and the internal liquid 7 expands and contracts with the temperature change, so that the internal liquid 7 flows out from the liquid junction 4 excessively. No air or sample solution enters the internal liquid 7 via the liquid junction 4.

  Furthermore, since the movable plug 8 can easily move in the reference electrode support tube 3a following the movement of the liquid level of the internal liquid 7, the movable plug 8 follows the liquid level of the internal liquid 7 and moves downward. When it moves, air flows into the upper part of the movable plug 8 from the vent 5, and the pressure of the upper air layer 9 of the movable plug 8 and the pressure of the internal liquid 7 can always be kept in balance. For this reason, the outflow of the internal liquid 7 from the liquid junction part 4 becomes smooth, and the liquid junction potential can be reduced.

  The present invention is not limited to the above embodiment.

  When the electrode 10 according to the present invention is of a composite electrode type in which a comparison electrode part and a working electrode part are integrated, the working electrode part is not limited to the pH electrode part 2, but other ion-selective electrodes. Part.

  However, the electrode 10 according to the present invention is not limited to a composite electrode type in which the comparison electrode unit 1 and the ion selective electrode unit such as the pH electrode unit 2 are integrated, and may be a single comparison electrode. Good.

  Further, the internal liquid 7 of the electrode 10 according to the present invention is not limited to a gel-like body, and may be a liquid. For example, when the internal liquid 7 is a KCl solution, the movable stopper 8 is placed on the liquid surface to suppress moisture evaporation from the internal liquid 7, thereby preventing the deposited KCl from clogging the liquid junction 4. Can do.

  In addition, it is needless to say that some or all of the above-described embodiments and modified embodiments may be appropriately combined, and various modifications can be made without departing from the scope of the invention.

Sectional drawing which shows the structure of the electrode which concerns on one Embodiment of this invention (AA sectional view taken on the line of FIG. 2). The figure which shows the whole structure of the pH meter in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Support pipe 4 ... Liquid junction part 6 ... Internal electrode 7 ... Internal liquid 8 ... Movable stopper 81 ... Fine particle 10 ... Electrode

Claims (5)

A support tube provided with a liquid junction;
An internal liquid filled in the support tube;
An internal electrode immersed in the internal liquid;
A liquid junction for electrical connection between the internal solution and the sample solution;
And a movable stopper made of fine particles, which is mounted on the liquid level of the internal liquid and is movable in the support tube following the movement of the liquid level.   The comparative electrode according to claim 1, wherein the fine particles have a particle size of 0.05 to 3 mm.   The comparative electrode according to claim 1 or 2, wherein a space between the fine particles is filled with a hydrophilic polymer, oil, or grease.   The comparative electrode according to claim 1, 2, or 3, wherein the internal liquid is a gel-like body.   An ion selective electrode comprising the comparative electrode according to claim 1, 2, 3 or 4.