Reduced and total glutathione and cysteine profiles of citrus fruit juices using liquid chromatography

A liquid chromatography assay for the determination of different species of glutathione and cysteine in fruit juices is described. The method is based on derivatization of thiols with 2-chloro-1-methylquinolinium tetrafluoroborate followed by chromatographic separation and UV-absorbance detection and quantitation. The method is linear in wide range of concentrations with a regression coefficient better than 0.99. The detection limits for glutathione and cysteine were 0.1 and 0.05 μmol L−1, respectively. Analytical recovery and the imprecision for both analytes were in the ranges 99.1–101.3% and 2.0–9.0%, respectively. The method was successfully applied to analysis of orange and grapefruit juices for reduced and total glutathione and cysteine.