Portal de Periódicos da CAPES

The reaction of ninhydrin with keratin proteins

1973; Elsevier BV; Volume: 54; Issue: 2 Linguagem: Inglês

10.1016/0003-2697(73)90361-8

1096-0309

Mendel Friedman, L. David Williams,

Bee Products Chemical Analysis

A simple method for quantitative analysis of chitosan based on the ninhydrin reaction is described. Only the 2-amino-2-deoxy-β-d-glucopyranose (GlcN) units of chitosans were found to form coloured products with ninhydrin. This reaction of chitosans with ninhydrin was sensitive and reproducible. Linear calibration curves were obtained in the concentration range of 10–120 mg/l, depending on the chemical composition of the chitosans. The amount of colour produced per GlcN unit decreased with decreasing fraction of acetylated units (FA). This imperfect stoichiometry was studied in more detail by comparing a series of β-(1→4)-linked GlcN oligomers. Dimer, trimer and tetramer produced 82, 67 and 61% of the colour relative to that of the monomer, respectively. The yield of almost fully deacetylated chitosan (FA=0.01) with different molecular weights reached a constant value at 40% when the degree of polymerization increased to more than 10. Differences in reaction rates were also observed. While monomer, dimer and chitosan with FA=0.6 reacted rapidly, other chitosans did not fully complete the reaction within 30 min. Due to this behaviour, the reaction of chitosans with ninhydrin might be used for quantitative analysis only when a reliable calibration against a reference of a similar FA is available.