JPH03267395A - Production of oxalate ion selective electrode by formation of silver oxalate coating film - Google Patents

Abstract

PURPOSE:To coat the surface of silver with slightly soluble silver oxalate and to obtain a superior material as an electrode or sensor for measuring the concn. of oxalate ions by immersing the silver in an aq. soln. contg. an oxalate and a soluble silver salt, supplying small electric current and causing cathodic polarization. CONSTITUTION:An oxalate such as dimethyl oxalate and a water soluble silver salt such as silver nitrate are dissolved in water to prepare an aq. soln. Degreased and cleaned silver is immersed in the soln., small electric current is supplied with Pt, etc., as the anode and the silver is subjected to cathodic polarization to stick a coating film of very slightly soluble silver oxalate to the surface of the silver with satisfactory adhesion. When the quantity of electric current supplied is made as small as <=0.4mA/dm<2>, the silver oxalate coating film can be formed without depositing metallic silver and a material effective as an electrode or sensor for measuring the concn. of oxalate ions is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION By coating the surface of metallic silver with sparingly soluble silver oxalate, the present invention provides a microscopic ion-selective electrode that responds to the concentration of oxalate ions, which are biological metabolic products. It can be made into stool and used to measure concentration or as a sensor.

Traditionally, equipment such as ion chromatography has been used to measure oxalate ions, and the electrode method is a simple method, although it is possible to use an ion electrode in which silver oxalate is brought into contact with metallic silver. ,in this case.

It has the following disadvantages and has not been put into 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 a container, which prevents the formation of minute objects.

4) It is complicated to create.

5) Response is slow.

6) Complicated shape and difficult to handle.

The present invention overcomes these drawbacks and provides fast response.

We succeeded in creating an electrode that exhibits a stable potential using a simple method, making it possible to create small, easy-to-handle electrodes at a low cost. Therefore, this electrode can be used not only for quantitative analysis of oxalate ion concentration in a solution, but also for miniaturization.

In addition, since the response speed is fast, it can be used as an oxalate ion sensor or a biosensor involving oxalate by combining it with an enzyme reaction.

From these points, the present invention is a useful invention.

Seven methods of the present invention will be explained below.

1) Dissolve oxalate ester in water.

2) Dissolve a soluble silver salt in water and add it to the solution in (■).

3) Degrease metallic silver and immerse it in the above solution.

4) Using platinum or the like as an anode, a very small current is passed to cathodically polarize metal silver.

By the above-described treatment, silver oxalate can be adhered to the metal surface in the form of a film with good adhesion.

The principle of this method can be briefly described as follows.

Oxalate esters dissolve in aqueous solutions and are gradually hydrolyzed to produce oxalic acid. The produced oxalic acid reacts with dissolved silver ions to produce sparingly soluble silver oxalate. This reaction maintains the solution at a high saturation of silver oxalate.

Silver oxalate is deposited on the surface of metallic silver by passing a minute current in this solution and cathodically polarizing the metal.

In this case, 9 the important point is that unless the cathode is polarized at an extremely small current density of 0.4 mA/dm2 or less, metallic silver will eutectoid and a good electrode cannot be produced.

With this method, metallic silver is not eutectoid.

A silver oxalate film is formed on the surface of metallic silver, making it possible to create a minute oxalate ion-selective electrode, and this method of creation is unprecedented.

Depending on the type of silver salt, pH adjustment may be required.

The time required to create the electrode also depends on the current density and temperature of the solution.

Since it differs depending on the type of reagent, it will be explained below by showing typical examples.

Example 1 Reaction solution Dimethyl oxalate Silver nitrate Temperature without pH adjustment Metal current density 0° 10 g/d m13 5 g/dm3 70°C Silver edge 4 m A/d m2 When experimented with the above configuration, the reaction time was 30 minutes. An electrode was fabricated, and this electrode showed a linear relationship between the S degree and the logarithm of the electrode potential, and the response time was within 30 seconds for oxalic acid solutions in the concentration range of 10-4 to 10-'M.

Example 2 Reaction solution Diethyl oxalate Silver nitrate pH Temperature metal current density without pH adjustment 00 5 g/drr + 3 5 g/d m3 50°C Silver plate 4 mA/dm" Reaction solution Dimethyl oxalate Silver nitrate pH Temperature metal current density Log/dm 3 5g/dmi 2, 0 70℃ Silver edge 0, 2mA/dm2 When we conducted an experiment with the above configuration, the electrode could be created in 15 minutes, and the response to oxalate ions was the same as in Example 1. However, compared to the case of Example 1, the V adhesion is inferior.

When an experiment was conducted using the above configuration, an electrode could be prepared in 60 minutes, and the response to oxalate ions was the same as in Example 1.

Example

Claims (1)

[Claims] Metallic silver is immersed in an aqueous solution containing an oxalate ester and a soluble silver salt, and a minute current is passed through the metal silver to cathodically polarize it, thereby creating an electrode in which a film of silver oxalate is generated on the surface of the metal silver. Method