Peracetic acid concentration meter

A membrane covered type peracetic acid concentration meter that measures concentration of peracetic acid in a sample solution, the peracetic acid concentration meter comprising:

• a membrane that allows peracetic acid to permeate;
• an internal solution that dissolves peracetic acid having permeated the membrane;
• a working electrode and a counter electrode that are immersed in the internal solution, such that an oxidation-reduction reaction of the permeated peracetic acid continuously occurs at surfaces of the working electrode to maintain a constant electric current through the electrodes for a predetermined time duration, thereby allowing the concentration meter to accurately measure the concentration of peracetic acid in the sample solution;
• and
• a protective material provided on a surface of the membrane on a sample solution side except in a region proximate the working electrode, the protective material being impermeable to liquid, wherein
• a buffer solution having a buffering effect on hydrogen ion concentration is the internal solution, and
• the working electrode is in contact with the membrane via an intermediate membrane having wettability with respect to the internal solution.