Analysis of N-acetylcysteine, D-penicillamine and L-cysteine in human plasma by capillary electrophoresis with LIF detection

N-acetylcysteine is a biologically active compound used as a mucolytic agent, as a nephroprotective agent and to treat poisonings, mainly those due to acetaminophen. In poisoning cases, its action is thought to be the increase of cysteine available to form glutathione, one of the most important endogenous detoxifiers in the human body. N-acetylcysteine is also commonly found in nutritional supplements studied for body-builders. However, it can cause severe side effects, such as potential damage to heart and lungs and an "anaphilactoid" reaction including rash, asthma and hypotension. D-penicillamine is another thiolic compound widely used in the treatment of poisonings, due to its chelating properties, and as an immunosuppressant in the therapy of rheumatoid arthritis. It is a dimethyl analogue of cysteine and can cause severe side effects such as aplastic anaemia, toxic myopathy and autoimmune responses . For this reason, it is important to have at disposal reliable analytical methods to monitor the plasma levels of N-acethylcysteine, D-penicillamine and L-cysteine. The proposed method is based on capillary electrophoresis coupled to laser-induced fluorescence detection (CE-LIF). Analyte separation was obtained by using a fused silica capillary and a background electrolyte composed of basic carbonate buffer, applying a 20 kV voltage. Direct hydrodynamic injection of samples was carried out after an original microwave-assisted derivatisation step with iodoacetamidoaminofluorescein (IAF). The method sensitivity allows the determination of N-acetyl-cysteine, D-penicillamine and L-cysteine levels down to 10 ng/mL. Preliminary results are promising and method validation is currently in progress for subsequent application to human plasma samples.