Enantioselective high-performance liquid chromatography assay of (+)R- and (-)S-alpha-lipoic acid in human plasma.

A specific plasma level assay for the enantiomers of alpha-lipoic acid is described. It makes use of liquid-liquid extraction, chemical reduction to the dithiol enantiomers, and their precolumn chiral derivatisation with o-phthalaldehyde in the presence of D-phenylalanine. The two diastereomeric derivatives are separated by reversed-phase HPLC with fluorescence detection.

High-performance liquid chromatographic assay for the determination of the decapeptide cetrorelix, a novel luteinizing hormone-releasing hormone antagonist, in human plasma.

This is the first paper which describes a HPLC method for the determination of the decapeptide cetrorelix, a potent luteinizing hormone-releasing hormone (LH-RH) antagonist, in human plasma by liquid-liquid extraction, concentration by back-extraction with diluted acid into a smaller volume, and fluorescence detection, using the decapeptide D-21740 as internal standard. The excitation (227 nm) and emission wavelengths (340 nm) for cetrorelix and the internal standard are identical. The extraction yield for both peptides is ca.