Abstract
An Improved analytical method based on precolumn derivatization with 9-fluorenylmethyl chloroformate (9-FMC) and reverse- phase liquid chromatography was developed for quantitative analysis of methionine, cysteine, and lysine In feeds. Samples of corn, whey powder, soybean meal, meat meal, and fish meal were selected for an accurate determination of these 3 amino acids. A portion of each finely ground sample was weighed and subjected to oxidation with performic acid for 16 h before hydrolysis with 6N HCI for 24 h. An aliquot of each hydrolysate was evaporated, dissolved, and diluted with 0.2M pH 7.85 borate buffer. An aliquot of each final solution was derlvatlzed with 9-FMC and analyzed by reverse- phase liquid chromatography using a fluorescence detector with a 254 nm excitation filter and a 313 nm emission filter. The 2 sulfur amino acids and lysine were perfectly separated from all other amino acids with a simple binary gradient. Cysteine (analyzed as cysteic acid), methionine (as methionine sulfone), and lysine were quantltated using internal standard calibration. Hydrolysates were also analyzed by conventional Ion-exchange chromatography (IEC). Amino acid values as obtained by the proposed LC method were close to IEC data. Considering IEC results as reference values, the differences In recovery of amino acids In feedstuffs determined by both methods were not more than 7.5%. Precision of the LC method was evaluated within a single hydrolysate and between different hydrolysates of a single sample. Coefficients of variation (CV) were not more than 4.1 and 5.9%, respectively.
