JPH11258197A - Liquid junction member for reference electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid junction member in which a liquid is hard to clog for a long period, in which the potential difference between liquids is small and whose response is fast by a method wherein a plurality of microcapillaries are bundled and they are used as the liquid junction member for a reference electrode. SOLUTION: For example, the liquid junction part of a reference electrode in a pH meter is provided with a liquid junction member 2 in which a plurality of microcapillaries 3 are bundled. The liquid member 2 is formed in such a way that a plurality (several tens to several hundreds) of glass tubes to the same composition as a body for the reference electrode, i.e., of SiO2 -Al2 O3 -PbO-Na2 O-K2 O-based lead glass tubes are inserted into, and passed through, lead glass tubes of the same composition, that the lead glass tubes are stretched and worked at a temperature of 650 to 700 deg.C so as to become the microcapillaries 3 having straight single-hole through holes 7 in about 10 to 100 μm and that the lead glass tubes are diced to a prescribed length. Thereby, the flow velocity in the leak of an internal liquid in the reference electrode becomes fast, the stability of a diffusion potential on the liquid contact interface of a sample is enhanced, and the generation of the potential difference between liquids is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid junction member in a reference electrode for various measuring instruments such as an ion concentration meter for pH and the like, an ORP meter (redox potential meter), polarography and voltammetry.

[0002]

2. Description of the Related Art For example, for measuring pH, a pH meter having a pair of a glass electrode a and a reference electrode b is used as shown in FIG.

In FIG. 5, c is a body for a glass electrode, and d is the pH welded to the glass electrode body c.
Responsive glass, e is a glass electrode inner electrode, f is a glass electrode inner liquid, h is a body for a reference electrode, i is a reference electrode inner electrode, j is a reference electrode inner liquid, and m is a liquid junction member.

In such a pH meter, generally,
The body h for the reference electrode includes, for example, SiO ₂ —Al ₂ O
₃ and lead glass _{-PbO-Na 2 O-K 2} O system, SiO
_{2 -B 2 O 3 -Al 2 O} 3 system and SiO ₂ -B ₂ O ₃ -N
a ₂ O-based borosilicate glass is used, and for the liquid junction member m, a porous ceramic specially prepared so as to match the expansion coefficient with the lead glass or borosilicate glass of the body h for the reference electrode is used. Have been.

In a pH meter in which a glass electrode and a reference electrode are combined and integrated, a lithium-based glass mainly composed of SiO ₂ and Li ₂ O is generally used as the pH-responsive glass. As the body for the glass electrode and the body for the comparison electrode, the above-described lead glass and borosilicate glass are used to match the expansion coefficient with the pH-responsive glass.

[0006]

However, when the porous ceramic is specially prepared so as to match the expansion coefficient of the body h for the reference electrode, the cost of the liquid junction member m is very high. In addition, the ceramic itself has high physical adsorptivity, and the reference electrode inner electrode (AgCl) f
Ag ⁺ and AgCl ₂ ⁻ dissolved from the solution cause AgCl to be deposited and contaminated at the contact interface between the ceramic and the sample liquid, and thus there is a problem that the ceramic porous channel is easily clogged.

When the liquid junction member m is contaminated as described above, not only the leakage of the liquid j in the comparison electrode becomes slow, but also a potential difference between the liquids is generated to cause an error in the measurement of the ion concentration.
Since porous ceramics easily absorb sample liquid,
During the liquid replacement, a potential difference between the liquids was apt to occur, and the potential variation became large depending on the sample history.

In addition, the quality characteristics of the ceramic itself often vary, in which case the leakage amount (flow velocity) of the internal liquid j varies, and it has been very difficult to reduce this.

In addition, for example, in an ORP meter, platinum is used for the electrode, so lead glass whose expansion coefficient matches that of platinum is used for the body, and the liquid junction member is similarly porous. Quality ceramic is used,
The same disadvantages as above occurred.

The present invention has been made in view of such circumstances, and has as its object to provide a liquid junction member which is unlikely to cause liquid clogging over a long period of time, has a small inter-liquid potential difference, and has a high response. And

[0011]

The technical means adopted by the present invention to achieve the above object are as follows. That is, the invention according to claim 1 is characterized in that a plurality of microcapillaries are focused and used as a liquid junction member for a reference electrode.

The above-mentioned microcapillary has a straight single-hole-shaped through-hole, and has a higher flow rate when the internal liquid leaks to the sample liquid side than the porous ceramic.
The stability of the diffusion potential at the liquid contact interface of the sample is improved, and the occurrence of a potential difference between liquids is reduced.

Further, since the through holes of the micro capillaries are straight, liquid clogging is unlikely to occur, and since the liquid junction member is formed by consolidating a plurality of micro capillaries, some micro capillaries are clogged. Does not slow down the leakage of the internal liquid.

In particular, if the microcapillary is made of lead glass or borosilicate glass so as to match with the lead glass or borosilicate glass generally used as a body for an electrode, the expansion is achieved. The liquid junction member can be provided at a lower cost than in the case of preparing a porous ceramic so that the coefficients are matched.

Preferably, the inner surface of the microcapillary is subjected to a water-repellent treatment as described in claim 3, and when the water-repellent treatment is performed in such a manner, the flow velocity of the internal liquid at the time of leakage is higher. Faster and less clogged.

It is also preferable that the resistance of the internal liquid to leak to the sample liquid side is adjusted by adjusting the length of the microcapillary. By adjusting the length of the liquid junction member in this way, the leak time of the internal liquid can be adjusted.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a liquid junction portion of a comparative electrode 1 in a pH meter as an example of a reference electrode, and includes a liquid junction member 2 in which a plurality of microcapillaries 3 are focused.

As shown in FIG. 2, the liquid junction member 2 is made of a glass tube having the same composition as the body 4 for the reference electrode, that is, SiO ₂ —Al ₂ O ₃ —PbO—Na ₂ O. −
K ₂ O system of a plurality of lead glass tube 5 (several tens to several hundreds)
Is passed through a lead glass tube 6 of the same composition, so that the lead glass tube 6 becomes a microcapillary 3 having a straight single-hole through hole 7 of about 10 to 100 μm.
It is formed by stretching (re-drawing) at a temperature of about 700 ° C. and dicing it to a predetermined length.

According to the liquid junction member 2 having the above-described structure, as shown in FIG. 3, the microcapillary 3 has the straight single-hole through-hole 7, so that the comparative electrode is compared with the conventional porous ceramic. The flow velocity at the time of leakage of the internal liquid 8 is increased, the stability of the diffusion potential at the interface with the liquid in contact with the sample is improved, and the occurrence of a potential difference between liquids is reduced.

Further, since the through hole 7 of the micro-capillary is straight, contamination due to liquid clogging is unlikely to occur, and since the liquid junction member 2 is formed by concentrating a plurality of micro-capillaries 3, the one Even if liquid is clogged in the microcapillary 3 in the portion, the leakage of the internal liquid does not become slow.

Preferably, as shown in FIG. 3, the liquid junction member 2 constructed as described above is coated on its inner wall surface with a water repellent agent 9 such as silicon or a fluorine compound.
This makes the quality of the inner wall surface of the through-hole 7 in contact with the internal liquid (see FIG. 1) 8 uniform, so that the leakage velocity of the internal liquid 8 is stable without variation. And the reliability is improved, liquid clogging is less likely to occur, and stable performance characteristics can be maintained for a long period of time.

Since the length of the microcapillary 3 is proportional to the resistance when the internal liquid 8 leaks to the sample liquid side, the length of the microcapillary 3 can be adjusted by adjusting the length of the microcapillary 3. Outgoing time can be adjusted.

In the above embodiment, the microcapillary 3 is made of lead glass. However, as the body 5 for the reference electrode, an SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ system or SiO ₂ —
In the case of using B ₂ O ₃ -Na ₂ O-based borosilicate glass, fine capillary 3 in accordance with the this it is also to the steel borosilicate glass.

Incidentally, Table 1 shows the results of comparing the liquid junction potential difference between the liquid junction member 2 according to the present invention which has been subjected to the water repellent treatment and the conventional liquid junction member made of porous ceramic.

[0025]

[Table 1]

In this case, the reference electrode inner electrode (see FIG. 1) 1
Ag / AgCl was used as 0, and 3.3 as the internal liquid 8.
mol / l KCl solution, and B-7, B
-4 and B-9 each have a pH of 9.18 at 25 ° C,
The buffer standard solutions at about 4.01 pH and 6.86 pH are shown.

From Table 1, it can be seen that, in the case of the present invention, pH 1 to pH 1
In the range of 3, the deviation of the inter-liquid potential difference is stable within 2 mV, and in particular, the fluctuation of the inter-liquid potential difference between NaOH and HCl is 1/3 or less of the conventional one.

As shown in FIG. 4, the response of the comparison electrode 1 provided with the liquid junction member 2 according to the present invention to B4 → B9 → NaOH → B2 → HCl → B7.
It has been confirmed that when the liquid to be measured is replaced in the order of, the liquid junction potential is stabilized within 30 seconds even when the acid and alkali are replaced. In this case, Ag / AgC was used as the inner electrode of the comparison electrode.
and 3.33 mol / l KCl solution as the internal solution.

In the embodiment described above, the liquid junction member 2 in which the through-hole 7 has been subjected to the water-repellent treatment has been described. As a result, a remarkably high leakage flow velocity was obtained, and it is needless to say that the stability of the diffusion potential at the liquid contact interface with the sample was good, and the occurrence of a potential difference between the liquids was small.

The liquid junction member 2 according to the present invention is not limited to the above-described comparative electrode 1, but may be a composite electrode type pH meter in which a glass electrode and a comparative electrode are integrated, or a non-pH type pH meter such as Na ⁺
Needless to say, the present invention can be applied to a reference electrode for various measuring instruments such as a concentration meter for various ions, an ORP meter (redox potential meter), polarography, and voltammetry.

[0031]

As described above, the invention according to the first aspect is characterized in that a bundle of a plurality of fine capillaries is used as a liquid junction member for a reference electrode. In the liquid junction member of the above, since the through hole of the microcapillary is straight, liquid clogging is unlikely to occur, and the liquid junction member is formed by focusing a plurality of microcapillaries. Even if the microcapillary becomes clogged, the leakage of the internal liquid does not become slow.

In addition, the microcapillary has a straight single-hole through-hole, and the flow velocity of the internal liquid leaking to the sample liquid side is higher than that of the porous ceramic. The diffusion potential at the interface is good, the potential difference between liquids is small, and high reliability can be maintained for a long time.

In particular, when the microcapillary is made of lead glass or borosilicate glass so as to match with the lead glass or borosilicate glass generally used as a body for an electrode, expansion is achieved. The liquid junction member can be provided at a lower cost than in the case of preparing a porous ceramic so that the coefficients are matched.

Preferably, the inner surface of the microcapillary is subjected to a water-repellent treatment as described in claim 3, and when the water-repellent treatment is performed as described above, the flow velocity of the internal liquid at the time of leakage is higher. Faster and less clogged.

It is also preferable that the resistance of the internal liquid when the internal liquid leaks to the sample liquid is adjusted by adjusting the length of the microcapillary. By adjusting the length of the liquid junction member in this way, the leak time of the internal liquid can be adjusted.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid junction portion of a comparative electrode.

FIG. 2 is an explanatory view of forming a liquid junction member by re-drawing processing in which a part is taken out and enlarged and illustrated.

FIG. 3 is a cross-sectional view of a liquid junction member.

FIG. 4 is a graph showing a response example of a liquid junction potential.

FIG. 5 is an explanatory diagram of a conventional pH meter provided with a liquid junction member made of porous ceramic.

[Explanation of symbols]

 3: microcapillary, 8: internal liquid.

Claims (4)

[Claims] 1. A liquid junction member for an internal liquid and a sample liquid used for a reference electrode, wherein the liquid junction member for a reference electrode is formed by focusing a plurality of microcapillaries. 2. The liquid junction member for a reference electrode according to claim 1, wherein the microcapillary is made of lead glass or borosilicate glass. 3. The liquid junction member for a reference electrode according to claim 1, wherein a water-repellent treatment is performed on an inner surface of the microcapillary. 4. The reference electrode according to claim 1, wherein the resistance when the internal liquid leaks to the sample liquid side is adjusted by adjusting the length of the microcapillary. Liquid junction member.