Change of pH Values of Standard Buffer Solutions Preserved for a Long Time by Nagahiko KISHIMOTO, Hiroshi MATSUSHITA and Hiroji HIRONAKA Standard buffer solutions such as oxalate solution, phthalate solution, phosphate solution and carbonate Solution preserved in a bottle of polyethylene for five years were measured the change of their pH values. Generally, buffer solutions grew moldy and at the same time, increased its pH value. Phthalate solution was most stable and its pH change was within ±0.01.