Selective measurement of resonance Raman and absorption spectra of different charged species produced in the electrooxidation of N,N′-dimethyl- N,N′-diphenylbenzidine by means of a column electrolytic continuous-flow method

Abstract

A novel multi-functional flow-electrolysis spectrochemical measurement system was developed for electrochemical and spectrophotometric analyses of electrogenerated species in homogeneous solution. Both resonance Raman (RR) spectra and absorption spectra of electrolysed solutions were measured using continuous-flow controlled-potential electrolysis with a carbon-fibre column electrode, in which the quantitative electrolysis could be achieved instantaneously. The RR measurement became very easy with the help of the electrolysis current vs. potential curve at the column electrode and the absorption spectra obtained with the same solution. Decomposition and thermal absorption of the sample species could be avoided in the continuous-flow method. N,N′-Dimethyl- N,N′-diphenylbenzidine (MPB) cation radical (MPB +·) and dication (MPB 2+) were produced selectively by the electrooxidation of MPB in acetonitrile. The RR and absorption spectra of electrolysed solution of MPB were observed under different electrolysis conditions. The dependence of the absorption spectra on the applied potential revealed that MPB +· and MPB 2+ had absorption maxima at 476 and 512 nm, respectively. With excitation by an argon ion laser, the RR spectra of MPB +· and MPB 2+ were observed selectively using an image-intensified multi-channel photodiode-array detector. The present system can be applied to time-resolved RR measurements with a minimum gate time of 25 ms.