Ninhydrin reagent according to Stahl

Ninhydrin reagent is mostly used for the detection of amino acids. It basically gives a characteristic purple color on reaction with a-amino acids and other amino compounds, provided the pH of the reaction is 5.0 or higher. At an acid pH of 0.3, the reaction of ninhydrin with ornithinine and proline results in a red color product. Ninhydrin reagent can stay stable at room temperature in the absence of nitrogen atmosphere for upto 1 month in the ethylene glycol-sodium acetate solvent system.

1 g ninhydrin dissolved in 475 mL 1-butanol and 25 mL acetic acid

Ninhydrin reagent may be used for the quantitative determination of total protein content in tissue hydrolysates.