THE INFLUENCE OF NEUTRAL SALTS ON THE pH OF PHOSPHATE BUFFER MIXTURES

The results embodied in this report were obtained as preliminary data for a systematic study of the magnitude of errors produced by the presence of various substances in the use of phenol red for calorimetric determinations of hydrogen ion concentration in biological fluids. Neutral salts, present in all body fluids, are known to have an influence on dye color. There are available many tables of salt errors of indicators. In most cases these are given for one buffer mixture and one indicator concentration. The question arises as to the constancy of the salt error with change in indicator concentration, with change in the buffer concentration, and with change in the pH. Before this can be definitely answered it is necessary to study the effect of neutral salts on the true hydrogen ion concentration (as measured by the hydrogen electrode) for the entire range of the buffer and at various dilutions. S#rensen and Palitzsch (1) drew attention to the fact that the addition of neutral salt to buffer solutions altered the electrometric pH and pointed out that the entire change as observed by a calorimetric reading could not be called a salt error of the indicator. It is a well recognized fact that the addition of small amounts of neutral salt to dilute buffer solutions increases the hydrogen ion concentration as determined by the potential of the hydrogen electrode. At the present time all other electrometric and also calorimetric, titrimetric, and gasometric methods for the determination of H+ are standardized directly or indirectly by a hydrogen electrode system. In order to note the effects produced by a