Direct determination of reduced glutathione in biological fluids by Ce(IV)-quinine chemiluminescence

A simple, sensitive and selective chemiluminescence (CL) method is proposed for the determination of reduced glutathione (GSH) in biological fluids. This method is based on the fact that the weak CL of GSH oxidized with cerium(IV) can be greatly enhanced by quinine. The optimum conditions for the CL emission were investigated. The calibration curve for GSH was linear over the concentration range of 4.0 × 10⁻⁹-4.0 × 10⁻⁵ M with a detection limit of 5 × 10⁻¹⁰ M (S/N = 3). The R.S.D. was found to be 4.0% by 11 replicate determinations of 1.0 × 10⁻⁷ M GSH. It was also found that GSH and cysteine, the two often-coexisting thiol compounds in biological samples, exhibited a different CL sensitivity in the Ce(IV)-quinine system (the sensitivity of GSH was higher than that of cysteine). This leads to the successful use of the proposed method for the direct and selective determination of GSH in rabbit whole blood and rat brain microdialysate in the presence of cysteine. Moreover, compared to the classical 5,5′-dithiobis(2-nitrobenzoic acid) method, the present one has the advantages of simplicity and high sensitivity.