JPH0781981B2 - Preparation method of oxalate ion selective electrode by silver oxalate film formation - Google Patents

Description

The present invention provides a simple oxalate ion-selective electrode which responds to the concentration of oxalate ion, which is a bio-metabolite, by coating the surface of metallic silver with hardly soluble silver oxalate. It can be used for concentration measurement or as a sensor. Conventionally, instruments such as ion chromatography have been used to measure oxalate ions.
The electrode method, which is a simple method, can be an ion electrode of the type in which silver oxalate is brought into contact with metallic silver, but in this case, it has the following drawbacks and has not been put to practical use. 1) The potential is unstable because the metal cannot be completely covered. 2) Silver oxalate is easily desorbed from metallic silver. 3) It is necessary to put the electrode in the container, and it is not possible to make minute objects. 4) Creation is complicated. 5) Response is slow. 6) The shape is complicated and difficult to handle. The present invention has overcome such drawbacks and succeeded in producing an electrode having a fast response and a stable potential by a simple method,
Small and easy-to-handle electrodes can be made at low cost. Therefore, this electrode is not only for quantitative analysis of the oxalate ion concentration in the solution, but it can be miniaturized and has a high response speed.
By combining it with an oxalate ion sensor or an enzymatic reaction, it can be used as a biosensor involving oxalic acid. From these points, the present invention is an invention that has utility. The method of the present invention will be described below. 1) Dissolve oxalate ester in water. 2) Dissolve the soluble silver salt in water and add to the solution of 1). 3) Degrease metallic silver and soak it in the above solution. 4) As an anode of platinum or the like, a very small current is passed to cause cathodic polarization of metallic silver. By the above treatments, silver oxalate can be adhered to the metal surface in a film form with good adhesion. The principle of this method is briefly described as follows. Oxalic acid ester dissolves in an aqueous solution and gradually hydrolyzes to form oxalic acid. The generated oxalic acid reacts with the dissolved silver ions to form a sparingly soluble silver oxalate. This reaction keeps the solution highly saturated with silver oxalate. In this solution, a minute electric current is applied to cause the metal to undergo cathodic polarization, and silver oxalate is deposited on the metallic silver surface. In this case, the important point is that unless cathodic polarization is performed at an extremely small current density of 0.4 mA / dm ² or less, metallic silver is co-deposited and a good electrode cannot be prepared. By this method, a silver oxalate film was formed on the surface of metallic silver without co-depositing metallic silver, and it became possible to make a fine oxalate ion-selective electrode. This method was not available before. It is a thing. Depending on the type of silver salt, it is necessary to adjust the pH.
Since it differs depending on the temperature of the solution and the kind of the reagent, a typical example will be described below. Example 1 Reaction liquid Oxalic acid dimethyl ester 10 g / dm ³ Silver nitrate 5 g / dm ³ pH adjustment None Temperature 70 ° C. Metal silver wire current density 0.4 mA / dm ^{2 When an} experiment was conducted with the above configuration, an electrode was created in 30 minutes. This electrode can produce a linear relationship between the concentration and the logarithm of the electrode potential for an oxalic acid solution in the concentration range of 10 ^-4 to 10 ^-1 M.
The response time was within 30 seconds. Example 2 Reaction solution Diethyl oxalate 5g / dm ³ Silver nitrate 5g / dm ³ No pH adjustment Temperature 50 ℃ Plate current density of metallic silver 0.4mA / dm ^{2 When the} experiment was conducted with the above-mentioned configuration, the electrode was formed in 60 minutes. The responsiveness to oxalate ion was the same as in Example 1. Example 3 Reaction solution Oxalic acid dimethyl ester 10 g / dm ³ Silver nitrate 5 g / dm ³ pH 2.0 Temperature 70 ° C. Metallic silver wire Current density 0.2 mA / dm ^{2 When an} experiment was conducted with the above configuration, an electrode could be created in 15 minutes. The responsiveness to oxalate ion was similar to that of Example 1, but the adhesiveness was inferior to that of Example 1.

Claims (1)

[Claims] 1. A silver oxalate film is formed on a surface of metal silver by immersing the metal silver in an aqueous solution containing an oxalate ester and a soluble silver salt and applying a minute current to the metal silver to cause cathodic polarization. To make a broken electrode