The Ninhydrin Reaction Revisited: Optimisation and Application for Quantification of Free Amino Acids

The ninhydrin reaction is commonly used for the detection of amino acids. However, in the literature, different conditions with respect to the buffer system, its pH and concentration, type of organic solvent, incubation time, and temperature, as well as the concentrations of the reagents, are described. To identify the most suitable conditions, colour development with reagents of varying compositions and different reaction temperatures and times were investigated using asparagine as a model amino acid. Asparagine was selected since it is one of the most abundant free amino acids in many types of samples. The optimal reaction mixture consisted of 0.8 mol L