Voltammetric behavior and trace determination of Pb2+ at a mercury-free screen-printed silver electrode

Screen-printed silver electrodes (AgSPEs), without chemical modification, has been investigated as disposable sensors for the measurement of trace levels of Pb2+. potential segment analysis indicates that the formation of underpotential and bulk depositions of Pb is not strongly coupled on the AgSPE. The possibility of determining Pb2+ at trace levels using the reversible underpotential deposition peak was examined by square-wave anodic stripping voltammetry without removal of oxygen. Under the optimized analytical conditions, the obtained sensitivity, linearity, and detection limit are 0.355 muA/ppb, 5-80 ppb (r = 0.9992), and 0.46 ppb (S/N = 3), respectively. The electrode is quite stable for repetitive measurements. The interference effect was thoroughly studied with various metals and no significant change in current was found in the determination of 5 ppb Pb2+. The practical applications were demonstrated to measure trace Pb2+ in natural waters. (C) 2002 Elsevier Science B.V. All rights reserved

Precise blood lead analysis using a combined internal standard and standard addition approach with disposable screen-printed electrodes

We report here a highly accurate and efficient method for blood lead analysis (BLA) through the use of a disposable electrode. A new type of mercury-plated preanodized screen-printed carbon electrode, together with a thallium(III) internal standard, simplifies calibration and gives easily quantifiable signals for accurate BLA. A preanodization procedure improves the preconcentration ability of the working electrode through the effect of lead (Pb) cornplexing with an electrogenerated surface functional group, mainly > C=O. Under optimized conditions, the ratio of the anodic stripping peak Currents of Ph and TI (i.e.. i(Pb)/i(TI)) is linear against [Pb] in the window of 1-300 ppb with a correlation coefficient and detection limit (signal-to-noise ratio = 3) of 0.999 and 0.23 ppb, respectively. This approach was used to analyze blood samples (17 = 55) from workers at a local battery factory. The results are consistent with those obtained from graphite furnace atomic absorption spectroscopy and confirm the applicability of the proposed method. (c) 2004 Elsevier Inc. All rights reserved

Electrocatalytic reduction and determination of dissolved oxygen at a preanodized screen-printed carbon electrode modified with palladium nanoparticles

Efficient and stable electrocatalytic activity for the reduction Of 02 at activated screen-printed carbon electrodes modified with palladium nanoparticles (SPE*-Pd) was demonstrated in this study. X-ray photoelectron spectroscopy confirmed the formation of > C=O functional group on electrode surface during the preanodization procedure at 2.0 V (vs. Ag/AgCl). The existence of chloride moieties was also identified possibly from the organic binder of carbon ink used in SPE fabrication. Both > C=O and chloride functional groups were essential for the excellent stability of the SPE*-Pd. Electrochemical impedance spectroscopy verified the enhanced kinetic rate of oxygen reduction reaction at the as-prepared Pd nanoparticles. The SPE*-Pd showed ca. 250 mV positive shift in peak potential together with twice increase in peak current compared to those observed at a SPE-Pt. The calibration plot was linear up to 8 ppm of DO with sensitivity and regression coefficient of 4.49 mu A/ppm and 0.9936, respectively. The variation coefficient of i(pc) for 7 DO determinations with O-2-saturated pH 7.4 PBS was 2.1%. Real sample assays for ground and tap waters gave consistent values to those measured by a commercial dissolved oxygen meter

Flow injection analysis of chloramphenicol by using a disposable wall-jet ring disk carbon electrode

A preanodized screen-printed ring disk carbon electrode was applied to the determination of chloramphenicol (Ph-NO2, CAP) by flow injection analysis (FIA). By setting up the first irreversible reduction reaction of Ph-NO2 to Pb-NHOH at the disk electrode, the following reversible oxidation of hydroxylamine (Ph-NHOH) to the nitroso (Ph-NO) derivative can be monitored/collected at the ring electrode for CAP analysis. The interference from dissolved oxygen and others can thus be avoided by using this approach and precise CAP determination can be easily performed by FIA under aerobic conditions. Preanodization treatment helps to lower the overpotential of the electrochemical reaction of CAP and favors the selective detection in aqueous medium. Under the optimum conditions, ten repetitive determinations at I mu M and 10 mu M CAP resulted in relative standard deviations of less than 4%, indicating good reproducibility of the system. A linear calibration range of 0.1 - 20 mu M with a detection limit of 0.074 mu M (S/N= 3) was obtained. Veterinary pharmaceutics were finally analyzed by this sensor to validate its practical applicability

Improved voltammetric peak separation and sensitivity of uric acid and ascorbic acid at nanoplatelets of graphitic oxide

In this study, much improved voltammetric peak separation and sensitivity of uric acid and ascorbic acid was observed at a screen-printed carbon electrode modified with nanoplatelets of graphitic oxide (GO). Electrochemical sensing of uric acid and ascorbic acid was further used to explore the role of oxygen functionalities and edge plane sites on electrocatalysis at GO. We successfully apply a microwave-assisted hydrothermal elimination method to remove the oxygen-containing functional groups from the GO surface. The edge plane on GO can be retained and the density of oxygen-containing functional groups can be easily controlled by varying the microwave treatment temperature. Using this platform, such discrimination to peak separation is attributed to the very distinct behavior of uric acid and ascorbic acid to form hydrogen bonds with oxo-surface groups (especially COOH group) at GO. (C) 2010 Elsevier B.V. All rights reserved

Copper-palladium alloy nanoparticle plated electrodes for the electrocatalytic determination of hydrazine

The preparation of copper-palladium alloy nanoparticle plated screen-printed carbon electrodes (SPE/Cu-Pd) and their use for the electrocatalytic determination of hydrazine in pH 7.4 phosphate buffer solution is described. X-ray photoelectron spectroscopic study indicates that the SPE/Cu-Pd prepared by successive electrochemical deposition of Cu and Pd is possessed of strong perturbed electronic interaction with a high Pd/Cu atomic ratio. Flow injection analysis of hydrazine using the SPE/Cu-Pd shows a linear detection range of 2-100 mu M at an applied potential of +0.2 V versus Ag/AgCl with a current sensitivity and relative standard deviation of 0.21 mu A/mu M and 1.86%, respectively. The detection limit (S/N = 3) was 270 nM. Quantitative detection of hydrazine in cigarette tobacco was further demonstrated using the proposed electrode. (c) 2005 Elsevier B.V. All rights reserved

A nonenzymatic glucose sensor using nanoporous platinum electrodes prepared by electrochemical alloying/dealloying in a water-insensitive zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquid

We report here a nonenzymatic sensor by using a nanoporous platinum electrode to detect glucose directly. The electrode was fabricated by electrochemical deposition and dissolution of PtZn alloy in zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl2-EMIC) ionic liquid. Both SEM and electrochemical studies showed the evidences for the nanoporous characteristics of the as-prepared Pt electrodes. Amperometric measurements allow observation of the electrochemical oxidation of glucose at 0.4 V (vs. Ag/AgCl) in pH 7.4 phosphate buffer solution. The sensor also demonstrates significant reproducibility in glucose detection; the higher the roughness factor of the Pt electrode, the lower the detection limit of glucose. The interfering species such as ascorbic acid and p-acetamidophenol can be avoided by using a Pt electrode with a high roughness factor of 151. Overall, the nanoporous Pt electrode is promising for enzymeless detection of glucose at physiological condition

Screen printed carbon electrode modified with poly(L-lactide) stabilized gold nanoparticles for sensitive As(III) detection

Poly(L-lactide) stabilized gold nanoparticles (designated as PLA-Au-NP) with an average particle size of ca. 10 nm were used to modify a disposable screen-printed carbon electrode (SPE) for the detection of As(III) by differential pulse anodic stripping voltammetry. Gold modification was evaluated by cyclic voltammetry, whereas scanning electron microscopy and transmission electron microscopy revealed the size and distribution of gold nanoparticles. The PLA-Au-NP/SPE was applied effectively to detect toxic As(III) in HCl medium. Under the optimal experimental conditions, a linear calibration curve up to 4 ppm with a detection limit (S/N= 3) of 0.09 ppb was obtained. ne sensitivity was good enough to detect As(III) at levels lower than the current EPA standard (10ppb). Most importantly, the PLA-AU(NP)/SPE can be tolerable from the interference of Cu, Cd, Fe, Zn, Mn, and Ni and hence provides a direct and selective detection method for As(III) in natural waters. Practical utility of the PLA-AU(NP)/SPE was demonstrated to detect As(III) in "Blackfoot" disease endemic village groundwater from southwestern coast area of Taiwan (Pei-Men)

Clay as a dispersion agent in anode catalyst layer for PEMFC

We report here a hybrid support that substantially improves the dispersion of nanoparticles with different geometric shapes. Without the addition of any organic dispersant, the plate-like clays effectively disperse spherical carbon black (CB) particles in pulverized powder and 5 wt.% Nation co-solvent suspension. Fine dispersion of CB particles with an average diameter of 40-60 nm was achieved from the SEM morphology analyses. A 20 wt.% Pt catalyst was then prepared with various weight ratios of CB/clay hybrids by using the impregnation method and TEM studies confirmed the fine dispersion of Pt nanoparticles with an average diameter of 4-5 nm. Polarization measurements verified that by applying an appropriate quantity of clay modules in preparing anode catalyst layer can indeed enhance the fuel cell performance. In other words, we employed clay to improve the dispersion of CB and, in turn, to increase catalyst utilization in PEMFC. (c) 2006 Elsevier B.V. All rights reserved