Enhanced Electrochemical Response of Diclofenac at a Fullerene⁻Carbon Nanofiber Paste Electrode.

The requirements of the Water Framework Directive to monitor diclofenac (DCF) concentration in surface water impose the need to find advanced fast and simple analysis methods. Direct voltammetric/amperometric methods could represent efficient and practical solutions. Fullerene⁻carbon nanofibers in paraffin oil as a paste electrode (F⁻CNF) was easily obtained by simple mixing and tested for DCF detection using voltammetric and amperometric techniques. The lowest limit of detection of 0.9 nM was achieved by applying square-wave voltammetry operated under step potential (SP) of 2 mV, modulation amplitude (MA) of 10 mV, and frequency of 25 Hz, and the best sensitivity was achieved by four-level multiple pulsed amperometry (MPA) that allowed in situ reactivation of the F⁻CNF electrode. The selection of the method must take into account the environmental quality standard (EQS), imposed through the "watchlist" of the Water Framework Directive as 0.1 µg·L DCF. A good improvement of the electroanalytical parameters for DCF detection on the F⁻CNF electrode was achieved by applying the preconcentration step for 30 min before the detection step, which assured about 30 times better sensitivity, recommending its application for the monitoring of trace levels of DCF. The electrochemical behavior of F⁻CNF as a pseudomicroelectrode array makes it suitable for practical application in the in situ and real-time monitoring of DCF concentrations in water.