PROBLEM TO BE SOLVED: To detect the concentration of pernitric acid continuously (intermittently) at an appropriate frequency, and to apply it to monitoring the concentration of pernitric acid during sterilization. A current flowing when pernitric acid is oxidized on an electrode is detected, and the concentration of the pernitric acid is detected based on the magnitude of the detected current. Gold is used as the electrode. The concentration is detected based on the value of the current I when a potential E in the range of 800 to 1400 [mV vs Ag/AgCl] is applied to the electrode. A potentiostat 14 is used to detect the current, and the electrode is the working electrode 11 of the potentiostat. [Selection diagram]【課題】適度な頻度で過硝酸の濃度を連続的（間欠的）に検出することができ、殺菌を行う際の過硝酸の濃度の監視に適用できること。【解決手段】過硝酸が電極上で酸化されるときに流れる電流を検出し、検出した電流の大きさに基づいて当該過硝酸の濃度を検出する。電極として金を用いる。電極に８００～１４００〔ｍＶ ｖｓ Ａｇ／ＡｇＣｌ〕の範囲の電位Ｅを与えたときの電流Ｉの値に基づいて、濃度を検出する。電流の検出のためにポテンショスタット１４を用い、電極を当該ポテンショスタットにおける作用電極１１とする。【選択図】 図１
