Linearized multiple standard additions for the potentiometric determination of weak acids

Abstract

The feasibility of potentiometric determination of weak monoprotic acids by the multiple standard addition method is examined. A standard solution of pure weak acid is added to the solution containing an unknown amount of the same weak acid, alone or mixed with its conjugate base. The experimental data are processed by Gran-type plots, for which rigorous and approximate equations are obtained. It is shown that weak acids can be determined by multiple standard additions with a precision comparable with that of the usual kinds of potentiometric addition-methods. The validity range of the approximate equations is established. Linear equations similar to those of Hofstee, Scatchard, Lineweaver and Burk, and Scott are also obtained, by which aciditity constants can be determined together with equivalence volumes. The effects of systematic and random measurement errors are examined.