Development of unmodified and CTAB-modified carbon paste electrodes (CPE) for direct electrochemical analysis of nitrites in aquarium water and rat blood

The present paper deals with the development of a new and original hexadecyltrimethylammonium bromide (CTAB)-modified carbon paste electrode (CPE) dedicated for the direct analysis of nitrites in aquaculture and rat blood. The surface morphologies and contact angles of unmodified and modified CPEs were performed using Scanning Electron Microscopy (SEM), Optical Microscopy (OM) and sessile drop techniques, respectively. Cyclic Voltammetry (CV) was used to study the electrochemical behaviour of nitrites, whilst Differential Pulse Voltammetry (DPV) and Linear Sweep Voltammetry (LSV) techniques were used to investigate their quantitative analysis. DPV operating parameters were optimized and the optimum values were pulse height 0.4 V, scan increment 0.015 V, pulse width 0.01 s and step time 0.5 s. The repeatability and reproducibility of the CPE were studied, and the effect of some interfering ions was evaluated to highlight the selectivity of the electrode. The modified CTAB/CPE showed a good stability and proved to be more sensitive, leading to a Limit of Detection (LOD) of 0.034 mg L-1 and a Limit of Quantification (LQ) of 0.152 mg L-1. The elaborated sensors were applied with success for nitrites analysis in aquaria with CPE and in rat blood with CTAB/CPE, preparing human blood measurements in near future work.