A secondary pH of phthalate buffer was prepared by differential potentiometry method using a Baucke cell which is separated by sintered glass disk in the middle of cell – so called two-half cells. The method has been validated at 298 K with the purpose to evaluate its suitability for meeting the application requirement. The method validation parameters include accuracy (bias), precision (repeatability), and estimation of measurement uncertainty. It was found that both accuracy and precision of the method were good, which is indicated by their very low standard deviation (SD). The measurement uncertainty value of the method was estimated. Application of the validated analytical method for the measurement of phthalate buffer in an international comparative test (APMP.QM-K91) showed that the result was close to the APMP.QM-K91’s Key Comparison Reference Value.
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