A SIMPLE AND ACCURATE METHOD FOR THE DETERMINATION OF CHLORIDE IN BIOLOGICAL FLUIDS

Abstract

Several modifications of the classical Volhard method (1) for the determination of chloride have been proposed but none is entirely free from the drawbacks of the original procedure. One of the principal causes of error is that the end-point fades and is uncertain when the silver chloride precipitate is not removed before titration. This is due to the fact that AgCl is more soluble than AgSCN and therefore reacts with thiocyanate: AgCl + SCN’ = AgSCN + Cl’. In order to avoid this reaction and to make an accurate determination possible, AgCl has to be filtered off. This, however, introduces a new error, as, according to Kolthoff (2), a definite loss in silver ions occurs through adsorption on the precipitate. The possibility of retarding the reaction with the precipitate so that the end-point lasts long enough to afford an accurate result was studied by a number of authors, some of them being quoted by Peters and Van Slyke (3). While a satisfactory modification of Volhard’s method without removal of the silver chloride has not yet been published, efforts to replace his procedure by methods based on different principles have led to promising results. A number of those newer methods have been investigated and, while many of them give reliable results, only a few are at the same time simple enough to compete with the traditional Volhard procedure and its modifications. Consequently it has been concluded that the mercurimetric determination of chloride offers an especially favorable method for a rapid, simple, and accurate determination.