S-Nitrosothiols (RSNO) are composed of a NO group bound to the sulfhydryl group of a peptide or protein. RSNO are very important biological molecules, since they have many effects on human health. RSNO are easily naturally decomposed by metal ions, light, and heat, with different kinetics. They can furthermore undergo transnitrosation (NO moieties exchange), which is a crucial point in physiological conditions since the concentration ratios between the different nitrosothiols is a key factor in many physiopathological processes. There is therefore a great need for their quantitation. Many S-nitrosothiol detection and quantitation methods need their previous decomposition, leading thus to some limitations. We propose a direct quantitation method employing the coupling of capillary electrophoresis with a homemade capacitively coupled contactless conductivity ((CD)-D-4) detector in order to separate and quantify S-nitrosoglutathione and its decomposition products. After optimization of the method, we have studied the kinetics of decomposition using light and heat. Our results show that the decomposition by light is first order (k(obs) = (3.40 +/- 0.15) x 10(-3) s(-1)) while that using heat (at 80 degrees C) is zeroth order (k(obs,80 degrees C) = (4.34 +/- 0.14) x 10(-6) mol L-1 s(-1)). Transnitrosation reaction between S-nitrosoglutathione and cysteine was also studied, showing the possibility of separation and detection of all the products of this reaction in less than 2.5 min.3616 19821988Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)French Committee for the Evaluation of Academic and Scientific Cooperation with Brazil (COFECUB) [802-14]LabEx MICHEM for international mobility