Nano Structured Potentiometric Sensors Based on Polyaniline Conducting Polymer for Determination of Cr (VI)

Abstract

In this paper, a potentiometric sensor based on polyaniline conducting polymer for potentiometric determination of Cr (VI) ions is reported. Polyaniline was synthesized electrochemically (cyclic voltammetry method) onto a micro pencil graphite electrode (0.7 mm diameter) in the presence of HCl and diphenylcarbazide (termed as (PGE/PAni/DPC). Some initial experiments were performed in order to find out the optimized conditions for preparation of the introduced Cr (VI) sensor electrode. The plot of E vs. log [Cr (VI)], showed a linear response in the range from 1.0 × 10 −6 to 1.0 × 10 −1 M. High repeatability with the detection limit of 8.0 × 10M was obtained.Key Words : Chromium (VI), Potentiometric sensor, Polyaniline, Diphenylcarbazide IntroductionChromium is an element widely used in industrial activities such as chrome plating and electroplating, metal smelting and metallurgy to manufacture alloys, dye stuff industries, leather tanning and wood treatment.1,2 It exists in the environment as Cr (III) and Cr (VI) oxidation states, which present different chemical properties. Cr (III) is a stable and slightly soluble cation considered an essential microelement, while Cr (VI) is a soluble and mobile anion, known as a highly toxic pollutant, with mutagenic and carcinogenic effects.3,4 While chromium in its Cr (III) form is not considered a toxic element and is a required diet nutrient. In humans, Cr (VI) exposure caused marked irritation of the respiratory tract and ulceration and perforation of the nasal septum in workers in the chromate producing and using industries.Due to the high toxicity of Cr (VI), it is essential to determine Cr (VI) rather than the total chromium concentration using a rapid and simple method that can be applied in industrial and environmental fields.4,5 The chemistry of Cr (VI) is very dependent on the pH of solution. Under acidic conditions (pH=2-4) chromium ion is predominantly exist as HCrO 4 − and Cr 2 O 7 2− and under neutral or alkaline media it exist predominantly as chromate ion (Eqs. 1, 2).Several analytical techniques have been developed to detect chromium, ranging from visible-light spectrophotometry to ion chromatography, atomic absorption spectrometry, GC-MS, electron probe microanalysis, flow injection analysis-ICP, synchrotron X-ray microprobe, isotope dilution mass spectroscopy and etc. Most of them, however, do not distinguish the oxidation state of chromium, and only total concentrations are measured. When the discrimination of the chromium species is necessary, for example in environmental and biochemical studies, chemical sensors can be a good choice. 5-7Potentiometry is an analytical technique very used for monitoring because it presents a number of advantages, such as simplicity, low cost, short measurement time, selectivity, adequate precision and accuracy, as well as ability to determine the analytes in coloured and turbid samples.8 Also, it is possible to determine and differentiate between chemical species of one metal depending on the used compound as the sensing...

Comparison between Modified and Unmodified Carbon Paste Electrodes for Hexavalent Chromium Determination

“…The detection of Cr(VI) by the use of unmodified CPE in presence of DPC was effectuated indirectly. The mechanism of measurements is based on a redox reaction accompanied by complexation between the reduced species of Cr(VI) which is Cr(III) and the oxidized form of DPC which is diphenylcarbazone DPCO . …”