Cereal Chem 64:226-229   |  VIEW ARTICLE

Amino Acid Analysis of Feedstuff Hydrolysates by Precolumn Derivatization with Phenylisothiocyanate and Reversed-Phase High-Performance Liquid Chromatography.

R. G. Elkin and A. M. Wasynczuk. Copyright 1987 by the American Association of Cereal Chemists, Inc. 

Corn, peanut meal, two sorghum varieties, and a corn-soybean meal-based complete mixed feed were either untreated or oxidized with performic acid before hydrolysis with hydrochloric acid. Hydrolysate amino acids were derivatized with phenylisothiocyanate (PITC), and the resulting phenylthiocarbamyl (PTC) derivatives were separated and quantitated by reversed-phase high-performance liquid chromatography (HPLC). Aliquots of each hydrolysate were also analyzed for amino acids using cation-exchange chromatography (CXC) and postcolumn derivatization with ninhydrin. In general, amino acid values determined by reversed-phase HPLC compared favorably with those obtained by CXC. PITC reacts with both primary and secondary amino acids, and the PTC-amino acid derivatives formed are stable enough for automated analysis without on-line derivatization. In addition, noncorrosive buffers were used to elute the PTC-amino acids from the reversed-phase column, and a complete separation of 17 hydrolysate amino acids plus methionine dioxide and cysteic acid was achieved in 25 min (injection-to-injection time). A PITC- based amino acid analytical system composed of modular HPLC equipment provides a viable alternative to amino acid analyzers at approximately one-half of the cost, is generally easy to operate and maintain, and is readily adaptable to the analysis of compounds other than amino acids.