Amino acid analysis of feedstuff hydrolysates by cation exchange high performance liquid chromatography

Corn, peanut meal, and soybean meal samples were either untreated or oxidized with performic acid before hydrolysis; the amino acids were determined by cation exchange high performance liquid chromatography (LC) and conventional cation exchange LC using an amino acid analyzer (AAA). Reproducibility of each procedure was assessed by repeated injections of the same calibration standard solution over a period of several days. LC data were more precise with regard to coefficients of variation for amino acid retention times, but were more variable with regard to peak areas. Although some significant differences between methods were noted, feedstuff amino acid values obtained by LC and AAA compared very well. The only consistent differences observed within each feedstuff were that Phe and Tyr values were significantly lower when analyzed by LC compared with AAA. Results of this study suggest that modular LC instrumentation can be used to accurately and reproducibly analyze amino acids in feedstuff hydrolysates. Advantages of using ninhydrin derivatization for feedstuff analysis, as opposed to using o-phthalaldehyde or dansyl chloride, are discussed.