A novel approach to the sensing of weak bases

A weak base present in an unbuffered solution containing α-tocopherol (α-T) was found to give rise to a new peak (termed as the oxidation prepeak) on the voltammogram of α-T at a potential less positive than that for the oxidation peak of α-T. The half-peak potential of the oxidation prepeak for a weak base shifted to a positive value along with an increase in pKb of the base. On voltammograms of flunitrazepam, nitrazepam, bromazepam, chlordiazepoxide, and medazepam each in an acetonitrile solution containing 3 mM α-T and 50 mM LiClO4, the prepeak heights were proportional to their concentration. Based on these findings, a novel approach to the sensing of such weak bases by means of linear sweep voltammetry and controlled potential electrolysis using a flow-type electrochemical cell is proposed. Moreover, an electrochemical detection method for high-performance liquid chromatography (HPLC) was developed for determining benzodiazepines.