HPLC method for analysis of free amino acids in fish using o-phthaldialdehyde precolumn derivatization

Precolumn derivatization applying o-phthaldialdehyde (OPA) was used to anal yze free lysine, histidine, and ornithine, precursors of the respective bio genic amines cadaverine, histamine, and putrescine, which are considered in dicators of fish quality and safety. This method uses 75% methanol to elimi nate the use of strong acids as the extraction solution. Each analysis took 35 min, was reproducible, and allowed separation of primary amino acids in fish samples. A binary solvent delivery system coupled with a fluorescence detector and an Ultrasphere ODS column were utilized for HPLC separation. Linearity of the calibration curves was very good (r(2) = 0.99) for the ami no acids of interest. Minimum concentrations of detection were 40 pmol/ml f or histidine and lysine and 70 pmoL/mL for ornithine. Average recoveries we re 72% for lysine, 93% for histidine, and 98% for ornithine. This method us ed solvent gradient elution to study the levels of these analytes in mahi-m ahi, bigeye tuna, and flounder.