Ninhydrin-sodium molybdate chromogenic analytical probe for the assay of amino acids and proteins

A sensitive method has been proposed for the quantification of amino acids and proteins using ninhydrin and sodium molybdate as chromogenic substrates in citrate buffer of pH5.6. A weak molybdate-hydrindantin complex plays the role in the formation of Ruhemann's purple. The linear response for the amino acid, amino acid mixture and Bovine serum albumin is between 0.999 and 66.80μM, 1.52 and 38μM and 5 and 100μg/L, respectively. The molar absorptivity of the individual amino acid by the proposed reaction extends from 0.58×10⁴ to 2.86×10⁴M^-1cm^-1. The linearity equations for the proposed ninhydrin-molybdate for amino acid mixture is Abs=0.021×Conc (μM)-0.002. The applicability of the proposed method has been justified in food and biological samples in conjunction with Kjeldahl method.