Experimental and statistical analysis on a nanostructured sensor for determination of p-hydroxybenzoic acid in cosmetics.

In this research, differential pulse voltammetry (DPV) coupled with experimental design, was used for determination of p-hydroxybenzoic acid (PHB) in cosmetics. Optimization of effecting parameters was carried out based on rotatable central composite design (RCCD) and response surface methodology (RSM) at the surface of a nanostructured electrode for achieving the best sensitivity. Sol-gel process was used for synthesize of nickel titanate (NiTiO3) nanoceramics. The structural and morphological characterization of the nanoparticles was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Then the NiTiO3 nanopowders were used for surface modification of a carbon paste modified electrode (CPE). Surface characterization of the electrode was accomplished using SEM, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Under the optimized conditions, the voltammograms exhibited two linear dynamic ranges of 0.7-80.0 µM and 80.0-1000.0 µM for PHB with the detection limit of 62.0 nM (S/N = 3). Finally the NiTiO3 nanoceramics modified carbon paste electrode (NiTiO3/CPE) could be employed for the determination of PHB in real samples with satisfactory results.

A carbon paste electrode modified with a nickel titanate nanoceramic for simultaneous voltammetric determination of ortho- and para-hydroxybenzoic acids.

An electrochemical sensor is described for the simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB). The sensor consists of a carbon paste electrode modified with nickel titanate nanoceramics (NiTiO3/CPE). The NiTiO3 nanoceramics and the nanostructured modified CPE were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Differential pulse voltammetry indicates that the response to OHB (best measured at 0.90 V vs. Ag/AgCl) and PHB (measured at 0.80 V vs. Ag/AgCl) is significantly improved at the modified CPE compared to a bare CPE. The limits of detection (at S/N = 3) are 0.38 and 0.10 µM for OHB and PHB, respectively. The method was applied to the determination of the two isomers in peeling skin lotion and during the Kolbe-Schmitt reaction. Graphical abstract Nickel titanate nanoceramics (NiTiO3) were synthesized by a sol-gel method. Then, a carbon paste electrode modified with NiTiO3 (NiTiO3/CPE) was constructed. The modified electrode was applied to the interference-free and simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB).