Development of long-term stable reference electrode with fluoric resin liquid junction

Abstract

A porous polytetrafluoroethylene (PTFE) junction reference electrode with an air-tight inner solution chamber containing saturated potassium chloride (KCl) was developed for flow analysis. This reference electrode is not influenced by a change in the sample pressure, and is not necessary to supply the KCl inner solution. The pore size of the porous PTFE junction is about 150 μm, although the conventional porous ceramic junction is 0.1 ~ 0.3 μm. The large pore size of the porous PTFE junction promotes the continuous exudation of KCl from the liquid junction and the higher surface tension of PTFE is effective to prevent the overflow of KCl. The porous PTFE was made by putting 74% of PTFE powder and 26% of KCl powder in a mold, pressing with a pressure of 200 kgf cm −2, and sintering at 365 °C. The quantity of KCl exuded from the disposable reference electrode is closely related to the life of the electrode. The relationship between the diffusion rate of the PTFE reference electrode and its characteristics was investigated. The quantity of KCl exuded from this reference electrode was initially of the order of 10 −5 mol h −1 and decreased to the order of 10 −6 mol h −1 after a year. This is approximately one-tenth of that exuded in a conventional reference electrode with a ceramic junction. The junction potential of the developed reference electrode was stable in the pH range 2 ~ 12 with a total ionic strength of more than 10 −3 mol l −1. This reference electrode containing 8 ml of the KCl inner solution was able to be used continuously for one or two years.