SIMULTANEOUS DETERMINATION OF P-HYDROXYBENZOIC ACID, 2-PHENOXYETHANOL, METHYL-P-HYDROXYBENZOATE, ETHYL-P-HYDROXYBENZOATE, PROPYL-P-HYDROXYBENZOATE, ISO-BUTYL-P-HYDROXYBENZOATE, AND N-BUTYL-P-HYDROXYBENZOATE IN SENSELLE LUBRICANT FORMULATION BY HPLC

Application of the poly (POSS-octavinyl-co-N-methylacetamide-co-divinylbenzene) solid extraction column in analyzing preservatives

In this study, a special poly solid-phase extraction (in-tube SPE) column consisting of poly (POSS-octavinyl-co-N-methylacetamide-co-divinylbenzene) [poly (POSS-OS-co-DVB-co-NMA)] was prepared based on the chemical structure of the preservatives, and was used as medium for extraction analysis in combination with UPLC. The composition of polymer SPE was optimized and characterized; good scanning electron microscopy (SEM) properties and satisfactory porosity were obtained with 30% monomer (POSS-OS:DVB:NMA = 2 wt%:13 wt%:15 wt%) and 70 wt% porogenic solvent (PEG20000:DMSO:ACN = 10 wt%:50 wt%:10 wt%). The experimental parameters of the in-tube SPE-UPLC analysis were optimized systematically. Then, the in-tube SPE-UPLC method was applied for analyzing the beverage sample, and correlation coefficients (R²) > 0.99 were obtained for the linear relationship within limits of 0.1~5.0 μg mL^-1. Excellent extraction efficiency, good precision, and satisfactory limit of detection sensitivity between 0.03 and 0.10 μg mL^-1 were obtained. The recovery ranged from 71.5 to 88.0%, with RSD ≤ 6.1%. Furthermore, the proposed method has the features of simple sample pretreatment, high throughput, rapid analysis, cost-effectiveness, and satisfactory sensitivity. Hence, the developed in-tube SPE-UPLC method based on the poly (POSS-OS-co-DVB-co-NMA) SPE column can be potentially used for simple and sensitive detection of preservatives.

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).