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.
Description:
This thesis is submitted to the Department of Chemistry, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Science in Chemistry, August, 2016.
Cataloged from PDF Version of Thesis.
Includes bibliographical references (pages 130-142)