Sodium borohydride as a reducing agent for preparing ninhydrin reagent for amino acid analysis

Sodium borohydride, in place of stannous chloride or titanous chloride, is effective in the preparation of the ninhydrin reagent for automated amino acid analysis. The reagent, coupled with dimethyl sulfoxide as a solvent, a very stable ninhydrin solution which did not form precipitates in the flow lines of the analyzer.