Three methods for the determination of the degree of substitution at protein‐amino groups with special reference to substituted gelatins

Abstract Three methods for the determination of the degree of substitution at protein‐amino groups are examined and compared. The procedures are applied to benzenesulphonyl derivatives of gelatin. The formol titration and ninhydrin colorimetric procedures are generally applicable to soluble proteins and their soluble derivatives. The spectrophotometric method is also applicable to these materials when the substituting reagent contains a chromophoric group. In this method the tyrosine content of the protein must be low or not react with the reagent, or the chromophore of the substituent must not absorb light in the tyrosine absorption region. The agreement between the first two procedures is good, and the third method is also in good agreement when the above conditions are met.