Cysteine (Cys) and glutathione (GSH) have been identified as key players in redox-based defense and signaling under stress in plants. Here, we describe a new high-performance liquid chromatography assay for the determination of four different forms of Cys and GSH, based on reduction of disulfide bonds with tris(2-carboxyethyl)phosphine followed by derivatization with 2-chloro-1-methylquinolinium tetrafluoroborate and UV detection. The presented method allows facile determination of total, reduced, free and protein bound aminothiols in cucumber leaves. Via this simple yet efficient method very good precision as well as accuracy were obtained. Linearity in detector response was observed over the range of 5–100 μmol L⁻¹ for GSH and 1–20 μmol L⁻¹ for Cys. The LOQs for GSH and Cys were 5 μmol L⁻¹ and 1 μmol L⁻¹ homogenate of cucumber leaf, respectively.

An accurate, simple and sensitive method for simultaneous determination of total homocysteine (Hcy) and total cysteine (Cys) in human plasma has been developed and validated. Hcy and Cys play a major role in metabolism and cellular homeostasis. An elevated level of plasma Hcy is considered an important risk factor or marker for several diseases, in particular cardiovascular disease, while Cys is involved in a variety of important cellular functions such as protein synthesis, detoxification and metabolism. The proposed analytical procedure consists of reduction of title thiol dimers and unsymmetrical disulfides with tris(2-carboxyethyl)phosphine, and derivatization with 2-chloro-1-methylquinolinium tetrafluoroborate (CMQT) followed by pH-mediated stacking capillary electrophoresis separation and ultraviolet-absorbance detection of Hcy-CMQT and Cys-CMQT derivatives at 355 nm. Effective baseline electrophoretic separation was achieved using a standard fused-silica capillary (effective length 91.5 cm, 75 μm id) and 0.1 mol L⁻¹, lithium acetate buffer adjusted to pH 4.75. The limit of quantification (signal to noise ratio of 9) for derivatized Hcy and Cys in plasma was 2 μmol L⁻¹. The calibration curves obtained for Hcy and Cys in plasma showed linearity in the range 2–20 μmol L⁻¹, with R² = 0.9986 and 20–300 μmol L⁻¹, with R² = 0.9998, respectively. The relative standard deviation of the points of the calibration curve was lower than 7%. The method can be used for a routine monitoring of total Hcy and total Cys levels in plasma of human subjects.