pH and USP 791

Send us Fan MailThis week on Bench Boost Mike explains why accurate pH measurement is more complex than it appears, highlighting the effects from temperature, ionic strength, calibration technique, probe condition, and sample chemistry. He reviews pH theory of hydrogen ion activity (not just concentration) and the logarithmic meaning of pH changes, then describes how a pH probe functions as an electrochemical cell. He details temperature impacts on solution pH and electrode response (Nernst slope), notes automatic temperature compensation limits, summarizes USP <791> calibration buffers and allowable uncertainty.