Determination of pharmaceutical thiols by liquid chromatography with electrochemical detection: Use of an electrode with a conductive carbon cement matrix, chemically modified with cobalt phthalocyanine

An electrode made with a conductive carbon cement (CCC) matrix and modified with cobalt phthalocyanine was utilized for the detection of some thiols of pharmaceutical interest: captopril, thiopronine, penicillamine. The performance of the electrode and the influence of pH were examined by hydrodynamic voltammograms and compared with those of unmodified CCC and glassy carbon electrodes. Calibration curves were performed in aqueous solutions at acidic pH in the range 5x10(-6) to 1x10(-4)M. Stability experiments showed that electrode response in flowing solutions decreased about 1% for hour. Satisfactory liquid chromatographic (LC) separation by reverse phase was obtained for the three compounds. Limits of detection reached with LC were in the range of pmoles. The modified electrode showed quite satisfactory performance: good sensitivity, good stability and detection of low concentration of the examined thiols.