GRAN LINEARIZATION OF POTENTIOMETRIC WINKLER TITRATION

A method for Gran linearization of a potentiometric Winkler titration curve is presented and compared with photometric detection and second-derivative evaluation of the potentiometric titration curve. Potentiometric and photometric data for the same titration were recorded simultaneously using a two-channel A/D converter. The equivalence value of the Gran linearization was found to agree very well with the two other methods (coefficient of variance 0.03%). For the Gran linearization only few titration points have to be collected and, in contrast to the two other methods, titration points after the equivalence volume are not needed at all. This makes the Gran method easier and faster than the other two. The Gran function values in the beginning of the titration can also be used as the basis of a reliable method of predicting the equivalence volume and adapting the volume increments during the rest of the titration accordingly. With this method it was possible to perform a series of titrations in 1 min 50 s each.