Ai. Haj-yehia et al., Determination of lipoic acid and dihydrolipoic acid in human plasma and urine by high-performance liquid chromatography with fluorimetric detection, J CHROMAT A, 870(1-2), 2000, pp. 381-388
A highly sensitive method for the determination of ol-lipoic acid (LA) and
dihydrolipoic acid (DHLA) in human plasma and urine has been developed, Sam
ples were acidified and extracted with organic solvent, and the free sulfhy
dryls of DHLA protected as the dicarboxyethylate by treatment with ethylchl
oroformate. The free carboxylic function of LA and the SH-protected DHLA we
re converted into their amide derivatives with the strong fluorophore 2-(4-
aminophenyl)-6-methylbenzothiazole in the presence of a coupling agent and
a base catalyst. The resulting fluorescent amides of both LA and DHLA were
separated on a reversed-phase column (Ultrasphere C-8) using simple isocrat
ic elution with acetonitrile-water (80:20) and detected fluorimetrically (e
xcitation 343, emission 423 nm), The method is highly sensitive, reproducib
le, and is easily applied for the simultaneous determination of LA and DHLA
in biological samples. (C) 2000 Elsevier Science B.V. All rights reserved.