Electrochemical study of some 2-mercapto-5-R-ammino-1,3,4-thiadiazole derivatives using carbon paste electrodes

The electrochemical study of some 2-mercapto-5-R-ammino-1,3,4-thiadiazole d erivatives was made by cyclic and linear sweep voltammetry using a carbon p aste electrode (CPE, graphite/solid paraffin ratio 2:1) as working electrod e and an Ag/AgCl reference electrode. The current-potential curves were rec orded in anodic polarisation in -0.1 and + 1.3 V range using aqueous soluti ons and different buffers (between pH 1.2 and 10.0), with 20 or 50 mV s(-1) sweep rate. The oxidation peak appears between + 0.65 and + 0.70 V due to disulphides formation. The 5-phenyl derivative has two oxidation peaks, the first at + 0.45 +/- 0.03 V and the second at + 0.65 +/- 0.03 V. The oxidat ion potentials are pH dependent, decreasing from 0.9 +/- 0.1V at pH 1.2 to 0.6 +/- 0.1 V at a pH between 8.0 and 10.0. In some potential ranges depend ing on pK(a) of molecules the oxidation potential and oxidation current are pH independent. Simple, precise and accurate voltammetric methods for the determination of these compounds were developed and validated in 2.5 x 10(- 6)-7.5 x 10(-4) mol l(-1) concentration ranges. The detection limits were 2 .3 mu mol l(-1) for 5-ammino-, 12.3 mu mol l(-1) for 5-acetylammino-, 11.6 mu mol l(-1) for 5-allylammino-, and 1.2 mu mol l(-1) for 5-phenylammino-2- mercapto-1,3,4 thiadiazole derivatives. (C) 1998 Elsevier Science B.V. All rights reserved.