Micro volume voltammetric determination of 4-nitrophenol in dimethyl sulfoxide at a glassy carbon electrode

Abstract: This study presents a miniaturized instrumentation for the determination of a model electrochemically reducible compound, 4-nitrophenol, in micro volumes of dimethyl sulfoxide at the glassy carbon electrode. Several working configurations of a three-electrode system and different constructions of reference electrodes are described. Moreover, the problem of the removal of oxygen (which is rather difficult in micro volumes) complicating the determination by differential pulse voltammetry, especially in a cathodic potential range was successfully solved. It has been found that the interference of oxygen can be partly eliminated by square wave voltammetry which is less sensitive to the presence of oxygen in the sample. Special apparatus capable of removing dissolved oxygen from 20 mm³ of solution was also constructed and tested. It was verified that 4-nitrophenol can be determined in micro volumes of dimethyl sulfoxide by square wave voltammetry in the presence of dissolved oxygen (limit of quantification LOQ = 6.0 µmol dm⁻³) and by differential pulse voltammetry after the removal of dissolved oxygen (LOQ = 2.4 µmol dm⁻³). Both those methods are comparable with the determination in a macro volume (5.0 cm³), which has LOQ = 1.3 µmol dm⁻³. Graphical abstract: [Figure not available: see fulltext.].