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Abstract:  Although there is information concerning the accuracy and reliability of pH meters, there has been little or no information reported showing comparisons among pH values obtained from meters, indicator papers and sticks. In this study, the authors determined the pH value at room temperature of 32 commercially available pharmaceutical and household aqueous products using a Corning Model 220 pH meter; an inexpensive, hand-held pH meter; several narrow-pH-range, nonbleeding indicator pH-Fix sticks; Duotest Narrow pH Range Indicator Paper Strips and Universal Indicator Paper, pH 1 to 11. Results are presented. The authors conclude that the inexpensive, hand-held pH wand performed surprisingly well, compared to the more expensive Corning meter. There was also general agreement among the three color-based indicators and the two pH meters. However, the indicator strips were less accurate at pH 5 than either above or below this pH value. The most accurate color-based indicator of pH in this study appeared to be the Machery-Nagel narrow pH range, nonbleeding, pH-Fix indicator stick series.

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