KCl比較電極タイプのガラス複合電極を用いて低導電率試料のpHを正確に安定して測定することは，難しいといわれている。その理由は，比較電極からの高濃度KClの流出による比較電極内部液と被験溶液との間の液間電位差の変動と，KClによる試料のpH変化である。この本質的な問題解決のために，イオン液体を液絡材料に用いた新しい比較電極が提案された。イオン液体型比較電極タイプのpH電極（PUREIL電極）を用いると，試料の汚染が無く，純水やボイラー水などの10 mS m－1以下の低導電率試料のpHを正確に安定して測定できる。本稿では，イオン液体型pH電極を用いて10 mS m－1の希薄硫酸のpH測定例を紹介する。
It is difficult to measure accurately and quickly pH of low conductivity solutions by use of pH glass combination electrodes based on a KCl salt bridge (KClSB). The reasons are the variation of the liquid junction potential (LJP) between a KClSB and a sample solution, and the change of pH in the sample solution due to the leakage of the concentrated KCl from the liquid junction. In order to solve the intrinsic problems, a new reference electrode, where an ionic liquid was used as the material of liquid junction, has proposed. The pH glass combination electrode equipped with an ionic liquid salt bridge (PUREIL electrode) enables us to measure accurately and quickly pH of less than 10 mS m-1 sample solutions such as pure water and boiler water. In this paper, we show the pH measurement of 10 mS m-1 sulfuric acid solution by use of PUREIL electrode.