Determination of Sulfite in Water and Dried Fruit Samples by Dispersive Liquid-Liquid Microextraction Combined with UV-Vis Fiber Optic Linear Array Spectrophotometry

A simple and rapid dispersive liquid-liquid microextraction (DLLME) method was applied to preconcentrate sulfite ions from aqueous samples as a prior step to its determination by fiber optic-linear array detection spectrophotometry. The procedure is based on the color reaction of sulfite with o-phthaldialdehyde (OPA) in the presence of ammonia to form isoindole and extraction of the formed isoindole derivative using the DLLME technique. The conditions for the microextraction performance were investigated and optimized. The calibration graph was linear in the range of 2-100 mu g L(-1)with a detection limit of 0.2 mu g L-1. The relative standard deviation for five replicate measurements of 10 and 50 mu g L(-1)of sulfite were 2.8 and 2.0 %, respectively. Under the optimized conditions, the enrichment factor of similar to 133 was obtained from a sample volume of 10 mL. The proposed method was successfully applied to the sulfite determination in drinking water and in food samples

Determination of Acetaminophen in the Presence of Ascorbic Acid Using a Glassy Carbon Electrode Modified with Poly(Caffeic acid)

A stable electroactive thin film of poly(caffeic acid) was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The electrochemical behaviors of acetaminophen on poly(caffeic acid) modified glassy carbon electrodes (poly(CA)-GCEs) were investigated by cyclic voltammetry and square-wave voltammetry (SWV). The results obtained that the poly(CA)-modified electrode was exhibited excellent electrochemical activity on the oxidation of acetaminophen. The calibration curve for APAP was shown two linear segments: the first linear segment increases from 0.2 to 1.0 and second linear segment increases up to 10 mu M. Using the first range of this calibration plot, a detection limit of 0.026 mu M is obtained for acetaminophen using square wave voltammetry. The poly(CA) electrode is selective not only for the detection of acetaminophen in the presence of ascorbic acid, dopamine, p-aminophenol and uric acid but also selective for the simultaneous determination of these four species present in a mixture. Finally, the proposed method was successfully applied to analysis of acetaminophen in pharmaceutical tablets

Nafion-Graphene Composite Film Modified Glassy Carbon Electrode for Voltammetric Determination of p-Aminophenol

A Nafion-graphene (Nafion-GR) nanocomposite film modified glassy carbon electrode was fabricated by a simple drop -casting method, and used in the electrochemical detection of p-aminophenol (4-AP). Owing to the large surface area, good conductivity of GR and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of 4-AP. The electrochemical behaviors of 4-AP on Nafion/GR film modified glassy carbon electrodes were investigated by cyclic voltammetry and differential pulse voltammetry. A calibration curve is constructed in the same matrix, urine, as the unknown samples to be analyzed. The Nafion-GR film modified electrode was linearly dependent on the 4-AP concentration and the linear analytical curve was obtained in the ranges of 0.5-200-M with differential pulse voltammetry (DPV) and the detection limit was 0.051-M. The Nafion-graphene nanocomposite modified electrode exhibited good reusability than pure graphene modified GCE. This procedure can be used for the determi- nation of p-aminophenol in the presence of its degradation products and paracetamol. Finally, the proposed method was successfully used to determine p-aminophenol in local tap water samples in urine samples and pharmaceutical preparations

Electrochemical Sensing of Acetaminophen on Electrochemically Reduced Graphene Oxide-Nafion Composite Film Modified Electrode

An electrochemical sensor based on graphene-Nafion nanocomposite film for voltammetric determination of acetaminophen (APAP) was presented. A Nafion graphene oxide-modified glassy carbon electrode was fabricated by a simple drop-casting method and then graphene oxide was reduced at the glassy carbon electrode surface by electrochemical method. The resulting electrode [electrochemically reduced graphene oxide (ER-GO)/Nafion glassy carbon electrode (GCE)] was used to determine acetaminophen. The electrochemical behaviors of acetaminophen on Nafion/ER-GO modified glassy carbon electrodes (GCEs) were investigated by cyclic voltammetry and square-wave voltammetry. The results obtained that the Nafion/ER-GO/GC modified electrode was exhibited excellent electrochemical activity on the oxidation of APAP. The calibration curve for APAP was shown two linear segments: the first linear segment increases from 0.4 to 1.0 and second linear segment increases up to 10 mu M. The detection limit was determined as 0,025 mu M (2.5x10(-8) mol L-1) using SWV. Finally, the proposed method was successfully used to determine APAP in pharmaceutical preparations and urine samples

Square-wave stripping voltammetric determination of caffeic acid on electrochemically reduced graphene oxide-Nafion composite film

An electrochemical sensor composed of Nafion-graphene nanocomposite film for the voltammetric determination of caffeic acid (CA) was studied. A Nafion graphene oxide-modified glassy carbon electrode was fabricated by a simple drop-casting method and then graphene oxide was electrochemically reduced over the glassy carbon electrode. The electrochemical analysis method was based on the adsorption of caffeic acid on Nafion/ER-GO/GCE and then the oxidation of CA during the stripping step. The resulting electrode showed an excellent electrocatalytical response to the oxidation of caffeic acid (CA). The electrochemistry of caffeic acid on Nafion/ER-GO modified glassy carbon electrodes (GCEs) were studied by cyclic voltammetry and square-wave adsorption stripping voltammetry (SW-AdSV). At optimized test conditions, the calibration curve for CA showed two linear segments: the first linear segment increased from 0.1 to 1.5 and second linear segment increased up to 10 mu M. The detection limit was determined as 9.1 x 10(-8) mol L-1 using SW-AdSV. Finally, the proposed method was successfully used to determine CA in white wine samples. (C) 2013 Elsevier B.V. All rights reserved