The quantitative estimation of amino nitrogen by determination of bound copper with the flame photometer.

The measurement of combined copper has been used in a number of procedures for the quantitative determination of amino acids and peptides. Pope and Stevens (1) as well as Schroeder, Kay, and Mills (2) determined the combined copper iodometrically. Martin and Mittelmann (3) analyzed for copper with the polarograph. Woiwod (4) used the spectrophotometer to measure the color produced by the reaction of copper with diethyl dithiocarbamate. Spies and Chambers (5) described a simple spectrophotometric technique in which the blue color obtained when an excess of alanine is added to the combined copper is utilized. In this laboratory, the iodometric determination was found troublesome, the Woiwod procedure lengthy, and the Spies-Chambers method not reproducible when used on plant tissue that yielded colored or turbid hydrolysates. The present paper describes a simple and rapid method for estimating amino nitrogen in protein hydrolysates in which the combined copper is measured with the flame photometer. The results obtained by the flame photometric method are compared with those obtained by a modification of the Woiwod method (4).