THE ISOELECTRIC POINT OF A STANDARD GELATIN PREPARATION1

Abstract

Two samples of a standard gelatin were studied, both prepared according to published specifications and washed free from diffusible electrolytes. The isoelectric point of this material, determined in 4 ways, was close to pH 4.85. (1) The pH values of solutions of gelatin in water approached the limit 4.86 [plus or minus] 0.01 as the concentration of gelatin was increased. (2) The pH values of acetate buffers were unchanged by the addition of gelatin only at pH 4.85 [plus or minus]0.01. This gives the isoionic point of S0rensen, which is the isoelectric point with respect only to hydrogen and hydroxyl ions. (3) Gels of this gelatin made up in dilute HC1 or NaOH, or in dilute acetate buffers, exhibited maximum turbidity at pH 4.85 [plus or minus] 0.03. (4) Very dilute suspensions of collodion particles in 0.1 per cent gelatin solutions made up in acetate buffers showed zero velocity in cataphoresis experiments only at pH 4.80 [plus or minus] 0.01. No evidence was found for the assumption that gelatin has 2 isoelectric points at widely separated pH values.