A Novel Sensor for Simultaneous Detection of Dihydroxybenzene Isomers

Abstract

A novel, facile and low-cost electrochemical technique for the detection of dihydroxybenzene isomers (DHBIs), catechol (CC), hydroquinone (HQ) and resorcinol (RS), in aqueous system was developed. An attempt was made for the analyses of HQ, CC and RS in the same aqueous system by UV-Vis spectroscopy. UV-Vis spectrum of CC, HQ and RS exhibited absorbance maxima in PBS supported aqueous solution at 275.4, 288.6 and 273.2 nm respectively. But in the possible binary and ternary mixture of CC, HQ and RS, UV-Vis spectra showed single absorption peak instead of two and three separate peaks respectively. So, simultaneous detection of DHBIs was impossible by UV-Vis spectroscopy. Three electrodes electrochemical system was employed which was controlled by computer supported auto potentiostat. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were adopted as detection techniques. 2B pencil collected from the local stationary shop was used for fabricating working electrode termed as pencil graphite electrode (PGE) in the experiment. PGE electrode was characterized by Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDX). From the SEM it was seen that surface morphology of PGE was not smooth as conventional glassy carbon electrode (GCE) instead contained huge grooves as well. It indicates that the graphite rod of the pencil was not pure crystalline. From EDX it was seen that PGE surface are impure as propped up by SEM. Results showed that it is composed of 79.39% carbon, 10.03% Si, 3.06% O2, 3.49% Al, 2.68% Fe and trace amount of Mg and Ca. So a lot of defects and few foreign materials were present in the surface of PGE confirmed by both SEM and EDX. PGE was first modified electrochemically by ionic liquid (IL), [1-Hexylpyridinium hexafluorophosphate (HIL) or 1-Butyl-3-Methylimidazolium hexafluorophosphate (BIL)] and then used in detection analyte by CV and DPV. Modified electrodes were termed as HIL-PGE and BIL-PGE in total working process. Modified electrodes showed excellent electroanalytical activity effect on the redox reaction of DHBIs. Total analyses and detection processes were performed in phosphate buffer solution (PBS) at pH 7.0 which was used as supporting electrolyte. The influences of scan rate and concentration on the redox behavior of HQ, CC and RS in both HIL-PGE and BIL-PGE were discussed. The anodic peak current versus the concentration of HQ, CC and RS showed a linear relationship. The variation of peak current was also plotted with Square root of scan rate. The electrochemical processes were diffusion controlled. Variation of peak potential separation was plotted with scan rate. The anodic peak potential shift was positive, which was due to IR drop. HIL-PGE showed splendid selectivity and strong anti-interference for detection of HQ, CC and RS simultaneously in aqueous media with excellent results. The limit of detection (LOD) was calculated by signal-to-noise ratio (S/N = 3). In simultaneous detection, the LOD for HQ, CC and RS at HIL-PGE were 6.38 μML-1, 4.56 μML-1 and 19.6 μML-1 respectively and those were 9.09 μML-1, 8.15 μML-1 and 26.78 μML-1 respectively at BIL-PGE. The sensitivity for HQ, CC and RS is 448.49 μA/mM/cm2, 627.35 μA/mM/cm2 and 146.10 μA/mM/cm2 respectively at HIL-PGE and 525.21 μA/mM/cm2, 585.68 μA/mM/cm2 and 178.0 μA/mM/cm2 respectively at BILPGE in simultaneous detection.