Fast ultrasound-assisted treatment of urine samples for chronopotentiometric stripping determination of mercury at gold film electrodes

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HCl and H2O2 for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators. (c) 2006 Elsevier B.V. All rights reserved.

Electrochemical Oxidation of Hydroxylamine on Gold in Aqueous Acidic Electrolytes: An in Situ SERS Investigation

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Arrays of gold microelectrodes made from split integrated circuit chips

A simple and inexpensive way to fabricate arrays of gold microelectrodes is proposed. Integrated circuit chips are sawed through their middle, normal to the longest axis, leading to destruction of the silicon circuit and rupture of the gold wires that interconnect it with the external terminals. Polishing the resulting rough surface converts the tips of the wires embedded in the chip halves into arrays of gold microdisks of about 25 mu m diameter. The number of active microelectrodes (MEs), of an array depends on the number of pins in the chip, n, being typically (n/2)-4. These MEs can be used individually or externally interconnected in any combination. X-ray images of the chips and micrographs of the resulting surface of the polished arrays have revealed variable distances between neighbor MEs, which are, however, larger than 10 times the radius of the disks. This feature of the MEs prevents diffusional cross-talk between electrodes. The use of these microdisk electrodes for analytical purposes exhibits sigmoidal voltammograms, and chronoamperometric experiments confirm the nonlinear i vs. t(1/2) plots, typical for processes where radial diffusion prevails. Satisfactory uniformity was observed for the response of each electrode of an array, indicating similarity of geometry and disk areas. The potentialities of these MEs were demonstrated by the determination of cadmium at ppb levels using square wave voltammetry with preconcentration. Due to the relative ease with which these MEs can be manufactured and their good performance in (chemical) analysis, wide applications in electrochemistry and electroanalysis is envisioned.

Flow-through cell based on an array of gold microelectrodes obtained from modified integrated circuit chips

The construction of a flow-through cell incorporating an array of gold microelectrodes is described and its application to flow injection analysis with amperometric detection is presented, Simple modification of almost any conventional integrated circuit chip, used as an inexpensive source of pre-assembled gold micro-wires, leads to the rapid and successful preparation of arrays of 8-48 elements, the polymeric encapsulation material from the top face of the chip is removed by abrasion until the gold micro-mires (used to interconnect the silicon circuit to the external contact pins of the chip) are disrupted and their transversal (elliptical) sections become exposed. Once polished, the flat and smooth top surface of the gold microelectrode-array chip (MEAC) is provided with a spacer and fitted under pressure against an acrylic block with the reference and auxiliary electrodes, to form the electrochemical (thin-layer) flow cell, while the contact pins are plugged into a standard IC socket, This design ensures autonomous electric contact with each electrode and allows fast dismantling for polishing or substitution, the performance of flow cells with MEACs was investigated utilizing the technique of reverse pulse amperometry without oxygen removal, A method was established for the determination of the copper concentration in sugar cane spirit, regulated by law for beverages, Samples from industrial producers and small-scale (alembic) brewers were compared, With a 24 MEAC, a detection limit of 30 mu g I-l of copper (4.7 x 10(-7) mol l(-1) of Cu-II for 100 mu l injections) was calculated, Routine operation was established at a frequency of 60-90 determinations per hour, Intercomparison with atomic absorption spectrometric determinations resulted in excellent agreement.

Gold nanoelectrode ensembles for direct trace electroanalysis of iodide

A procedure for the standardization of ensembles of gold nanodisk electrodes (NEE) of 30 nm diameter is presented, which is based on the analytical comparison between experimental cyclic voltammograms (CV) obtained at the NEEs in diluted solutions of redox probes and CV patterns obtained by digital simulation. Possible origins of defects sometimes found in NEEs are discussed. Selected NEEs are then employed for the study of the electrochemical oxidation of iodide in acidic solutions. CV patterns display typical quasi-reversible behavior which involves associated chemical reactions between adsorbed and solution species. The main CV characteristics at the NEE compare with those observed at millimeter sized gold disk electrodes (Au-macro), apart a slight shift in E1/2 values and slightly higher peak to peak separation at the NEE. The detection limit (DC) at NEEs is 0.3 mu M, which is more than one order of magnitude lower than DL at the Au-macro (4 RM). The mechanism of the electrochemical oxidation of iodide at NEEs is discussed. Finally, NEEs are applied to the direct determination of iodide at micromolar concentration levels in real samples, namely in some ophthalmic drugs and iodized table salt. (c) 2006 Elsevier B.V. All rights reserved.

Modifying glassy carbon (GC) electrodes to confer selectivity for the voltammetric detection of L-cysteine in the presence of DL-homocysteine and glutathione

In this communication we report a proof of concept study of the use of cyclic voltammetry with a polyeugenol-modified glassy carbon (GC) electrode to selectively detect L-cysteine in the presence of both DL-homocysteine and glutathione in perchloric acid. The formation of a polyeugenol-modified gold electrode is also reported for the first time.

New label free CA125 detection based on gold nanostructured screen-printed electrode

This paper describes the optimisation and the analytical performances of a label-free impedimetric immunosensor for the detection of tumour marker CA125 based on gold nanoparticles modified screen-printed graphite electrode. Experimental conditions of each step for the developed immunosensor were studied and optimised. The immunosensor response varied linearly (r2 = 0.996) with antigen concentration between 0 and 100 U/mL. The estimated detection limit was 6.7 U/mL. The electrochemical immunosensor allowed unambiguous identification of CA125, while no significant non-specific signal was detected in the case of all negative controls. The analytical usefulness of the impedimetric immunosensor was finally demonstrated analysing serum samples. © 2012 Elsevier B.V. All rights reserved.

Synergistic electrocatalytic effect of nanostructured mixed films formed by functionalised gold nanoparticles and bisphthalocyanines

A synergistic electrocatalytic effect was observed in sensors where two electrocatalytic materials (functionalized gold nanoparticles and lutetium bisphthalocyanine) were co-deposited using the Langmuir-Blodgett technique. Films were prepared using a novel method where water soluble functionalised gold nanoparticles [(11-mercaptoundecyl)tetra(ethylene glycol)] (SAuNPs) were inserted in floating films of lutetium bisphthalocyanine (LuPc2) and dimethyldioctadecylammonium bromide (DODAB) as the amphiphilic matrix. The formation of stable and homogeneous mixed films was confirmed by pi-A isotherms, BAM, UV-vis and Raman spectroscopy, as well as by SEM and TEM microscopy. The synergistic effect towards hydroquinone of the electrodes modified with LuPc2:DODAB/SAuNP was characterised by an increase in the intensity of the redox peaks and a reduction of the overpotential. This synergistic electrocatalytic effect arose from the interaction between the SAuNPs and the phthalocyanines that occur in the Langmuir-Blodgett films and from the high surface area provided by the nanostructured films. The sensitivity increased with the amount of LuPc2 and SAuNPs inserted in the films and limits of detection in the range of 10(-7) mol L-1 were attained. (C) 2014 Elsevier B.V. All rights reserved.

The oxidation of hydroxylamine on Pt-, and Pd-modified Au electrodes in aqueous electrolytes: Electrochemical and in situ spectroscopic studies

The electrooxidation of hydroxylamine, NH2OH, in 0.1 M phosphate buffer (PB, pH = 7) on Pt-, and Pd-modified Au electrodes prepared by galvanic displacement of underpotential deposited Cu, was investigated by electrochemical techniques and three and in situ vibrational probes, substrate-induced surface enhanced Raman scattering, SI-SERS, surface enhanced infrared absorption, SEIRAS, and Fourier transform infrared reflection-absorption, IRAS, spectroscopies. Analyses of the results obtained made it possible to identify at low overpotentials, solution phase (sol) and adsorbed (ads) nitric oxide, NO, as well as solution phase nitrous oxide, N2O. As the potential was increased, the peak(s) ascribed to NO(ads) gained in intensity and new features associated with NO2−(ads) and NO2−(sol) were clearly discerned. Further excursion toward higher potentials yielded an additional peak assigned to NO2(ads). This behavior is analogous to that found for bare Au electrodes in a potential region in which the metal is at least partially oxidized under otherwise the same experimental conditions.