[Routine colorimetric method for the quantitative microanalysis of free alpha-amino nitrogen in protein hydrolysates]

The determination of alpha-amino nitrogen (alpha-AN) is performed via the formation of amino acid copper complexes and subsequent colorimetric estimation of the dissolved copper as copper diethyldithiocarbamate. The continuous colour reaction by means of an auto-analyzer increases the reliability of the measured values (variation coefficient = 1.7%) compared to the laborious manual method. The stability of the amino acid copper complexes and of copper diethyldithiocarbamate was verified and possible interferences with the colour reaction were discussed. Ammonia does not interfere with the determination of alpha-AN in protein hydrolysates, whereas traces of detergent residues bias the measured values.