Determination of ametryn in soils via microwave-assisted solvent extraction coupled to anodic stripping voltammetry with a gold ultramicroelectrode

An extraction-anodic adsorptive stripping voltammetric procedure using microwave-assisted solvent extraction and a gold ultramicroelectrode was developed for determining the pesticide ametryn in soil samples. The method is based on the use of acetonitrile as extraction solvent and on controlled adsorptive accumulation of the herbicide at the potential of 0.50 V (vs. Ag/AgCl) in the presence of Britton-Robinson buffer (pH 3.3). Soil sample extracts were analysed directly after drying and redissolution with the supporting electrolyte but without other pre-treatment. The limit of detection obtained for a 10 s collection time was 0.021 µg g-1. Recovery experiments for the global procedure, at the 0.500 µg g-1 level, gave satisfactory mean and standard deviation results which were comparable to those obtained by HPLC with UV detection.

Electroanalytical study of the antidepressant sertraline

Aflowinjection squarewave cathodic stripping voltammetric method has been developed for the determination of sertraline in a pharmaceutical preparation. The method shows linearity between peak current intensity and sertraline concentration for the interval between 0.20×10−6 and 1.20×10−6 mol L−1. Limits of detection and quantification were found to be 1.5×10−7 and 5.0×10−7 mol L−1, respectively. Up to 70 samples per hour can be analysed with a good precision (R.S.D. = 2.5%). The proposed method was successfully applied to the determination of sertraline in a commercial product. In the voltammetric determination of sertraline in flow, a high sample rate is obtained at reduced costs, opening the possibility to compete with the chromatographic methods generally used for this analysis.

Disposable Graphite Foil Based Electrodes and Their Application in Pharmaceutical Analysis

This paper explores a new source of graphite for working electrodes, which presents advantages such as low electrical resistance, good flexibility, favorable mechanical performance, versatility to design electrodes in almost any size and very low cost. The new electrodes were investigated in batch electrochemical cells as associated with flow injection analysis systems. Cyclic voltammetry, stripping voltammetry, and amperometry associated with flow injection analysis techniques were applied for the determination of ascorbic acid, zinc and paracetamol in pharmaceutical formulations, respectively. Well-established analytical methods were applied for comparison purposes. The results herein demonstrate the potential of graphite foils as working electrodes in different electroanalytical methods, offering the possibility of producing disposable sensors for routine applications.

Anodic Stripping Voltammetric Determination of Lead (II) and Cadmium (II) by Using a Carbon Nanotubes Paste Electrode Modified with Ion Exchange Synthetic Resin

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de um sensor de amálgama sólido para a determinação de enxofre em microemulsões de biodiesel

Pós-graduação em Química - IQ

Gold electrodes from recordable CDs for mercury quantification by flow injection analysis

The development of a new methodology for the construction of very efficient flow cells for mercury detection by potentiometric stripping analysis, employing the thin gold layer of recordable CDs as working electrode is reported. This new source of electrodes (CDtrodes) show very attractive performance, similar to that obtained with commercial gold electrodes, with superior versatility. The low cost of this new source of gold electrodes allows a frequent replacement of the electrode, avoiding cumbersome clean-up treatments. Various experimental parameters have been optimized to yield low detection limits (0.25 ng/mL of mercury for 5 min deposition at 0.3 V) and good precision (standard deviation of 1.9% was obtained for 15 repetitive measurements using 10 ng/mL of mercury). Standard curves were found to be linear over the range of 0.5-100 μg L-1 of mercury. The flow cells developed were used for the quantification of mercury in oceanic and tap water. © Springer-Verlag 2000.

Determinação direta de molibdênio em comprimidos polivitamínicos por voltametria em meio não aquoso

Adsorptive stripping voltammetry carried out in a homogeneous ternary solvent composed of N,N-dimethylformamide, water and ethanol, with alpha-benzoinoxime (alphaBO) as the complexing agent for Mo(VI) and a 0.5 mol L-1 acetic acid - sodium acetate buffer as supporting electrolyte was successfully used for the determination of molybdenum in polyvitamin-polymineral tablets. Tablet samples were analyzed and the results were compared with those obtained both by graphite furnace atomic absorption and by recovery tests, with good correlations, indicating that this may be considered as an alternative procedure for routine determination of Mo(VI) in pharmaceutical samples.

Voltammetric determination of dialifos in soils with a mercury film ultramicroelectrode

An extraction-adsorptive stripping voltammetric procedure for the determination of the pesticide dialifos in soil samples using microwave-assisted solvent extraction and a mercury film ultramicroelectrode was developed. The method is based on the use of hexane-acetone solvent (1:1, v/v) and on controlled adsorptive accumulation of the insecticide at the potential of -0.10V (versus Ag/AgCl) in the presence of Britton-Robinson buffer (pH 2.0). Soil sample extracts were analyzed directly after drying and redissolution with the supporting electrolyte, but without other pretreatment. The limit of detection obtained for a 10sec collection time was 2.0x10-8 mol L-1. Recovery experiments for the global procedure, at the 0.100µgg-1 level, gave satisfactory average and standard deviation results for the two different soils tested.

Detection of Arah1 (a major peanut allergen) in food using an electrochemical gold nanoparticle-coated screen-printed immunosensor

A gold nanoparticle-coated screen-printed carbon electrode was used as the transducer in the development of an electrochemical immunosensor for Ara h 1 (a major peanut allergen) detection in food samples. Gold nanoparticles (average diameter=32 nm) were electrochemically generated on the surface of screen-printed carbon electrodes. Two monoclonal antibodies were used in a sandwich-type immunoassay and the antibody–antigen interaction was electrochemically detected through stripping analysis of enzymatically (using alkaline phosphatase) deposited silver. The total time of the optimized immunoassay was 3 h 50 min. The developed immunosensor allowed the quantification of Ara h 1 between 12.6 and 2000 ng/ml, with a limit of detection of 3.8 ng/ml, and provided precise (RSD <8.7%) and accurate (recovery >96.6%) results. The immunosensor was successfully applied to the analysis of complex food matrices (cookies and chocolate), being able to detect Ara h 1 in samples containing 0.1% of peanut.

Electroquímica de sustancias de interés en los sistemas agroalimentario y de sanidad animal. Desarrollo de biosensores electroquímicos. Aplicaciones analíticas.Electrochemistry of substances of interest in agroalimentary and animal health systems. Development of electrochemical biosensors. Analytical applications.

Se estudiarán los mecanismos de reacción electroquímica de las micotoxinas (metabolitos tóxicos generados por hongos) citrinina (CIT), patulina (PAT) y moniliformina (MON), de los antioxidantes naturales alfa, beta, gama y delta tocoferoles, de los flavonoides fisetina (FIS), morina (MOR), luteolina (LUT), rutina (RUT), buteina (BUT), naringenina (NAR) y miricetina (MIR) y de las hormonas esteroides estradiol (EDIOL), estrona (EONA) y estriol (ETRIOL). Por otra parte, se implementarán técnicas electroanalíticas para la detección y cuantificación de estos sustratos en muestras de matrices naturales que los contengan. Se realizará el diseño y caracterización de biosensores enzimáticos a partir de peroxidasas y/o fosfatasa alcalina para la determinación de la micotoxina CIT y de los flavonoides y, por otro, de inmunosensores para las micotoxinas ocratoxina A (OTA) y PAT y hormonas. Para el anclaje de enzimas y/o anticuerpos, se estudiarán las propiedades de electrodos modificados por monocapas autoensambladas, nanotubos de carbono y partículas magnéticas. Se usarán las técnicas de voltamperometría cíclica, de onda cuadrada y de redisolución con acumulación adsortiva, espectroscopías de impedancia electroquímica, electrólisis a potencial controlado, uv-vis e IR, microbalanza de cristal de cuarzo y microscopías de alta resolución (SEM, TEM, AFM). La importancia de este proyecto apunta a la obtención de nuevos datos electroquímicos de los sustratos indicados y conocimientos relacionados con la aplicación de electrodos modificados en la preparación de biosensores y en el desarrollo de técnicas alternativas para la determinación de los analitos mencionados precedentemente. Electrochemical reaction mechanisms of mycotoxins (toxic metabolites generated by fungi) citrinin (CIT), Patulin (PAT) and moniliformin (MON), natural antioxidants alpha, beta, gamma and delta tocopherols, flavonoids fisetin (FIS), morin (MOR), luteolin (LUT), rutin (RUT), butein (BUT), naringenin (NAR), miricetin (MIR) and steroid hormones estradiol (EDIOL), estrone (EONA) and estriole (ETRIOL) will be explored. On the other hand, electroanalytical techniques for the detection and quantification of these substrates in samples of natural matrices will be implemented. The design and characterization of enzymatic biosensors from peroxidases and/or from alkaline phosphatase for the determination of CIT and flavonoids, and also of inmunosensors for ochratoxin A (OTA) and PAT and hormones will be performed. For the anchor of enzymes and/or antibody, properties of electrodes modified by self assembled monolayers, carbon nanotubes and magnetic particles will be explored. Cyclic, square wave and adsorptive stripping voltammetries, electrochemical impedance spectroscopy, controlled potential electrolysis, uv-vis and IR, quartz crystal microbalance and high-resolution microcopies (SEM, TEM, AFM) will be used. The importance of this project is aimed at obtaining new electrochemical data for the indicated substrates and knowledge on the application of modified electrodes in preparation of biosensors and in the development of alternative techniques for the determination of the above-mentioned analytes.

Análise potenciométrica de redissolução com ultramicroeletrodos: fundamentos e aplicações na determinação de metais traços

The Potentiometric Stripping Analysis (PSA) is described with emphasis on ultramicroelectrode applications with a laboratory developed computer based instrumentation. The technique potentialities as compared with the voltammetric approach are pointed out based on the current literature. Some results of trace metals analysis including zinc, cadmium, lead and copper in vinegar and canned food samples are presented. The mainly advantage found in our laboratory was the technique capability to analyse natural samples with minimum matrix interference and the low level of noise found in our determinations.

Determinação direta de molibdênio em comprimidos polivitamínicos por voltametria em meio não aquoso

Adsorptive stripping voltammetry carried out in a homogeneous ternary solvent composed of N,N-dimethylformamide, water and ethanol, with alpha-benzoinoxime (alphaBO) as the complexing agent for Mo(VI) and a 0.5 mol L-1 acetic acid - sodium acetate buffer as supporting electrolyte was successfully used for the determination of molybdenum in polyvitamin-polymineral tablets. Tablet samples were analyzed and the results were compared with those obtained both by graphite furnace atomic absorption and by recovery tests, with good correlations, indicating that this may be considered as an alternative procedure for routine determination of Mo(VI) in pharmaceutical samples.

Determinação voltamétrica por redissolução anódica de Cu(II) em águas residuárias empregando um eletrodo de pasta de carbono modificado com quitosana

The electrochemical applications of a CPE modified with chitosan for the determination of Cu(II) in wastewater samples using anodic stripping voltammetry are described. The best voltammetric response was observed for a paste containing 25% m/m of chitosan. A 0.10 mol L-1 NaNO3 solution (pH 6.5) as supporting electrolyte, a pre-concentration potential of -0.20 V, pre-concentration time of 270 s and a scan rate of 25 mV s-1 were selected. The calibration graph was linear in the Cu(II) concentration range from 2.0 x 10-7 to 7.4 x 10-6 mol L-1, with a detection limit of 8.3 x 10-8 mol L-1.

The use of a gold disc microelectrode for the determination of copper in human sweat

A novel approach of using a gold disc microelectrode to analyze sweat samples for copper ions by anodic square wave stripping voltammetry (SW stripping voltammetry) is described Sweat was collected from the lower back of four subjects after physical exercise and the sample volume required for the determinations was 100 mu L. Under the optimized conditions the calibration plot was linear over the range 1-100 mu mol L(-1) Cu(II) with a limit of detection of 0 25 mu mol L(-1) The precision was evaluated by carrying out five replicate measurements in a 1 mu mol L(-1) Cu(II) solution and the standard deviation was found to be 1 5% Measurements were performed by inserting the microelectrode into sweat drops and Cu(II) concentrations in the analyzed samples ranged from 09 to 28 mu mol L(-1) Values obtained by the proposed voltammetric method agreed well with those found using graphite furnace atomic absorption spectroscopy (GFAAS) (C) 2010 Elsevier B V All rights reserved

Compact disks, a new source for gold electrodes. Application to the quantification of copper by PSA

In this work we describe a versatile and very sensitive way for copper quantification by potentiometric stripping analysis using gold electrodes obtained from recordable compact disks (CDs). This new source of electrodes (CDtrodes) shown similar performance to the commercial gold electrodes with superior versatility and lower cost. Recordable CDs contains a highly pure gold film with thickness between 50 and 100 nm and superficial area of ca. 100 cm(2). The working electrode developed was used successfully in stationary cell and many experimental parameters have been optimized. For copper, the detection limit attained was 30 ng L-1 (600 s deposition time) with remarkable precision (standard deviation of 1.8 % for 20 repetitive measurements using 25 mu gL(-1) of copper with 60 s of deposition time). The gold electrode developed was used for analysis of copper in sugar cane spirits and tap water samples. The results were compared with those obtained by atomic absorption spectroscopy.