Potentiometric detection of 2-mercaptobenzimidazole and 2-mercaptobenzothiazole at cobalt phthalocyanine modified carbon-paste electrode

A potentiometric method has been developed for determination of 2-mercaptob enzimidazole (MBIM) and 2-mercaptobenzothiazole (MBTH) based on cobalt phth alocyanine (CoPc) modified carbon-paste electrode. We show that the CoPc-mo dified electrode acts as a catalyst for the electrooxidation of MBIM and MB TH, lowering the overpotential of the reaction by 250 to 400 mV, compared t o the unmodified electrode. The faster rate of electron transfer results in a near-Nernstian behavior of the modified electrode and makes it a suitabl e potentiometric sensor for potentiometric detection of these sulfhydryl co mpounds. The potential response of the electrode to the sulfhydryl compound s has a linear dynamic range between 1 x 10(-6) and 3.6 x 10(-3) M with a n ear Nernstian slope of 50 to 54 mV/decade of concentration and a detection limit of 5 x 10(-7) M. The electrode retains its full activity for at least a month. The potentiometric response mechanism toward sulfhydryl compounds is discussed and a mechanistic model for the electrode response is given.