Development of a voltammetric sensor for chromium(VI) determination in wastewater sample

Screen-printed carbon electrode (SPCE) modified with poly-L-histidine film can be successfully applied for chromium(VI) determination based on its pre-concentration. Optimum adherence and stability of the POIY-L-histidine film was obtained by direct addition of PH solution 1% (w/v) on the electrode surface, followed by heating at 80 degrees C during 5 min. Linear response range, sensitivity and limit of detection were 0. 1-150 [mu mol L-1, 4. 13 LA mu mol L` and 0.046 mu mol L-1. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation, was measured as 3.2% for 10 experiments in 40 mu mol L-1 using the same electrode and 4.0% using screen-printed electrode as disposable sensor, respectively. The voltammetric sensor was applied to determination of Cr(VI) and indirect determination of Cr(III) in wastewater samples previously treated by a leather dyeing industry and the average recovery for these samples was around 97%. (C) 2006 Elsevier B.V. All rights reserved.

Adsorption of chromium(VI) by titanium(IV) oxide coated on a silica gel surface

Titanium(IV) oxide, coated on the surface of silica gel (surface area, 308 m2 g-1; amount of Ti(IV) per gram of modified silica gel, 1.8 x 10(-3) mol), was used to adsorb CrO4(2-) ions from acidic solutions. The exchange capacity increased at lower pH values and was affected to some extent by the acid used. The material was used to preconcentrate Cr(VI) from 0.5 ppm solutions of chromate very efficiently and virtually 100% recovery was achieved in every instance.

Sequential spectrophotometric determination of chromium(III) and chromium(VI) using flow injection analysis

A flow injection analysis (FIA) procedure for the speciation of Cr(III) and Cr(VI) using the 1,5-diphenylcarbazide (DPC) method is presented. As Cr(III) does not interfere in the Cr(VI) - DPC reaction, both Cr(VI) and total chromium [after the on-line oxidation of Cr(III) by Ce(IV)] are sequentially determined. Cr(III) is obtained by difference. Under the experimental conditions described, the calibration graphs are linear up to 2 μg mh1 of Cr(VI) and 4 μg ml-1 of Cr(III). The detection limits found were 18 ng ml -1 for Cr(VI) and 55 ng ml-1 for Cr(III), at a signal to noise ratio of 3. The common interfering elements in the Cr(VI) - DPC reaction were investigated under dynamic FIA conditions. The FIA method was also compared with the conventional spectrophotometric procedure.

Screen-printed carbon electrode modified with poly-L-histidine applied to voltammetric determination of chromium (VI)

The present work reports the use of a screen-printed carbon electrode (SPCE) modified by poly-L-histidine film to determine chromium (VI). Stable films can be formed by direct addition of PH solution 1 % (w/v) on the electrode surface, followed by heating at 80°C during 5 min. Calibration curves can be constructed for Cr(VI) from 1.0 × 10-5 mol L-1 to 7.0 × 10-5 mol L-1 Cr (VI) in acetate buffer pH 4 using a preconcentration step of 60s at open circuit potential. A relative standard deviation of 3.2% was for five determination of 4.0 × 10 -5 mol L-1 Cr (VI). The method was successful applied to determination of Cr(VI) in wastewater samples from a leather dyeing industry. copyright The Electrochemical Society.

Spectroscopic characterization of the reduction and removal of chromium (VI) by tropical peat and humin

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Eletrodos impressos modificados com poli-histidina aplicados na construção de sensores eletroquímicos para crômio(VI) e fármacos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determinação de rotina do crômio em fezes, como marcador biológico, pelo método espectrofotométrico ajustado da 1,5-difenilcarbazida

O objetivo deste estudo foi ajustar o método espectrofotométrico da 1,5-difenilcarbazida à determinação do crômio em fezes, como marcador biológico, adequando-o à rotina laboratorial. Fatores que poderiam exercer interferência na transformação do crômio (III) à crômio (VI) foram testados, como a recuperação do metal, quantidade de amostra, quantidade e ordem de emprego dos ácidos oxidantes da digestão úmida, temperatura e tempo de digestão e perda por volatilização do crômio como cloreto de cromila, porém não se determinou estatisticamente interferência destes fatores. No método ajustado, a amostra é digerida pela clássica mistura ácida nítrica/perclórica, levando a oxidação do crômio (III) a crômio (VI), e alíquota do extrato diluído é usado para reação com 1,5-difenilcarbazida; as absorbâncias são medidas a 550nm, utilizando-se de cubetas de um centímetro de caminho óptico, contra prova em branco conduzida simultaneamente. Dicromato de potássio foi empregado como substância de referência para obtenção da curva padrão na faixa de 0,25 - 2,5mg.mL-1 de Cr2O3 (1mg Cr2O3 º 1,9355mg K2Cr2O7).

Redução de crômio hexavalente por substâncias húmicas aquáticas imobilizadas em aminopropil sílica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Interação entre as substâncias húmicas de sedimentos e metais potencialmente tóxicos: um estudo na Bacia Hidrográfica do Turvo/Grande

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização e dinâmica de metais em rios da Bacia Hidrográfica do Turvo/Grande. -

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Recycling leather waste: preparing and studying on the microstructure, mechanical, and rheological properties of leather waste/rubber composite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Recycling leather waste: preparing and studying on the microstructure, mechanical, and rheological properties of leather waste/rubber composite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determination of chromium by GFAAS in slurries of fish feces to estimate the apparent digestibility of nutrients in feed used in pisciculture

This paper presents a simple, fast and sensitive method to determine chromic oxide (used as a biological marker of fish feed) in samples of fish feces by GFAAS through the direct introduction of slurries of the samples into the spectrometer's graphite tube. The standard samples of feces and of fish feed containing 0.10-1.00 mg kg(-1) of Cr2O3 were pre-frozen for I min in liquid nitrogen and then ground a cryogenic mill for 2 min, which reduced the samples' grain size to less than 60 mu m. The standard slurries were prepared by mixing 20 mg of standard samples of fish feed or feces with I mL of a solution containing 0.05% (v/v) of Triton X-100 and 0.50% (v/v) of suprapure HNO3 directly in the spectrometer's automatic sampling glass. The final concentrations of Cr2O3 present in the standard slurries were 2, 4, 8, 16 and 20 mu g L-1. After sonicating the mixture for 20s, 10 mu L of standard slurries were injected into the graphite tube, whose internal wall was lined with a metallic palladium film that acted as a permanent chemical modifier. The limits of detection (LOD) and quantification (LOQ) calculated for 20 readings of the blank of the standard slurries (2%, m/v of feces or feed devoid of minerals) were 0.81 and 2.70 mu g L-1 of Cr2O3 for the standard feces slurries, 0.84 and 2.83 mu g L-1 of Cr2O3 for the standard feed slurries. The proposed method was applied in studies of nutrient digestibility of different fish feeds and its results proved compatible with the results obtained from samples pre-mineralized by acid digestion. (c) 2005 Elsevier B.V. All rights reserved.

Evaluation of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for direct determination of chromium in medicinal plants

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The significance and determination by image analysis of microcrack density in hard chromium plating

It is well known that the microcrack density is a fundamental parameter in hard chromium electroplating. The chemical and mechanical properties of this coating are widely dependent on its microcrack density. In this paper a simple image analysis procedure to determine microcrack density is presented in order to demonstrate it as a fundamental tool to estimate the fatigue, corrosion and wear behavior, as well as the residual stress field of a coated component. For this purpose, the image analysis procedure was carried out on two kinds of hard chromium plating - one called accelerated (high velocity of deposition and fluoride-free) and the other conventional (with fluoride). The coatings were applied on samples of AISI 4340 aeronautical steel, which is widely used in aircraft landing gear components. To characterize the practical significance of this study, the microcrack density results were related to the fatigue, wear and corrosion behavior from previous study and to the residual stress field in the coatings.