Quantitation of free amino acids in plasma and muscle samples in healthy subjects and uremic patients by high-performance liquid chromatography and fluorescence detection.

An automatic on-line high-performance liquid chromatographic (HPLC) method is developed to quantitate free amino acids in the biological samples. The method is based on pre-column derivatization of amino acids with orthophthalaldehyde (OPA) in presence of 2-mercaptoethanol (2-ME). The derivatized amino acids were separated on a 5 micron C18 column using a multi-step gradient with two solvents and the detection was made at Eex = 340 nm and Eem = 450 nm. The results were highly reproducible with a relative standard deviation (RSD) between 0.5-2% for all amino acids. Each chromatographic run was completed within 40 min to separate 24 amino acids. The optimized method was applied to evaluate the levels of free amino acids in plasma and muscle samples of eight healthy subjects and 13 uremic patients under fasting conditions.