An electroanalytical method for the simultaneous determination of paracetamol (PAR), caffeine (CAF), and orphenadrine (ORPH) using the square‐wave voltammetry (SWV) and a cathodically pretreated boron‐doped diamond electrode was developed. The method exhibits linear responses to PAR, CAF, and ORPH in the concentration ranges 5.4×10−7–6.1×10−5 M, 7.8×10−7–3.5×10−5 M, and 7.8×10−7–3.5×10−5 M, respectively, with detection limits of 2.3×10−7 M, 9.6×10−8 M, and 8.4×10−8 M, respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in pharmaceutical formulations.

We describe the analytical performance of a hybrid material composed of SiO 2 , Al 2 O 3 and TiO 2 . It was prepared by a sol-gel process and can act as an adsorbent in the continuous-flow enrichment of copper. A minicolumn was packed with the material, copper ions are adsorbed at pH 9.13, then eluted with 1.0 mol L −1 nitric acid, and determined by FAAS. The material was characterized by infrared spectroscopy, scanning electron and energy dispersive spectroscopy, energy dispersive X-ray fluorescence analysis, powder Xray diffraction, and specific surface area analysis. No significant interference was observed for most ions in up to copper/ interferent ratios of 1:100 and of 1:500 in case of Ca(II), Ba (II), and Mg(II). The breakthrough capacity is 1.4 mg g −1 under dynamic conditions. The limits of detection and of quantification are 0.50 and 1.4 μg L −1 , respectively, and the calibration plot is linear in the range from 5.0 to 245.0 μg L −1 (r00.999). The relative standard deviation is 3.20 (for n07 and at a Cu(II) concentration of 10 μg L −1 ). The method was applied to the determination of trace copper ions in water, vegetable and alcohol fuel samples.

Carbon black (CB) grafted with 3-mercaptopropyltrimethoxysilane (3-MPTMS) was used as solid phase extractor for Cd 2+ in a flow injection system coupled to flame atomic absorption spectrometry (FAAS). The influence of pH, buffer concentration, preconcentration flow rate and eluent concentration on preconcentration of Cd 2+ were investigated by means of chemometric tools. The characterization of the adsorbent chemically modified was performed by Fourier transform infrared, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, Raman spectroscopy and textural analysis. To perform the on-line preconcentration, 20.0 mL of a pH 7.0 Cd 2+ solution at a flow rate of 4.0 mL min −1 was loaded through 30.0 mg of modified CB and then eluted with 1.0 mol L −1 HCl toward the FAAS instrument. The limits of detection and quantification were found to be 0.20 and 0.66 µg L −1 , respectively. Addition and recovery tests carried out in real samples (mineral, tap and saline waters, and cigarette sample) and the analysis of certified reference material (TORT-2, lobster hepatopancreas reference) attested the applicability of proposed method.

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In the present paper the assessment of a novel molecularly imprinted polymer, poly(methacrylic acid)/silica, for clean-up and selective extraction of cholesterol in milk samples is described. The relative selectivity coefficient (k) values for cholesterol/5-α-cholestane and cholesterol/7-dehydrocholesterol systems were found to be 5.08 and 6.08, respectively, thus attesting the selectivity of the MIP for cholesterol under competitive adsorption with structurally analogous steroid compounds. The milk analysis was initially based on saponification followed by liquid-liquid extraction with n-hexane. Then, the protocol of molecularly imprinted solid phase extraction (MISPE) was carried out by loading the milk hexanic extract through 200 mg of MIP or NIP (non-imprinted polymer) packed into SPE cartridges at a flow rate of 0.6 mL min(-1). The washing step was performed by using n-hexane followed by further elution with ethanol and HPLC-UV analysis at 208 nm. From the breakthrough curve the maximum adsorption capacity of the MIP towards cholesterol was found to be 29.51 mg g(-1). The precision of the MISPE protocol was assessed as intra- and inter-days yielding RSD (relative standard deviations) lower than 4.10%. Cleaner HPLC chromatograms were obtained for milk samples submitted to the MISPE protocol in comparison to the solid phase extraction using the NIP or modified octadecyl silica (C18). Recoveries varying from 96.6 up to 102.2% for milk samples spiked with cholesterol were achieved, thus ensuring the accuracy of the proposed method.

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Recebido em 13/11/06; aceito em 27/4/07; publicado na web em 16/10/07 EFFECTS OF OPERATIONAL PARAMETERS ON THE PHOTODEGRADATION OF DIRECT RED 23 AZO DYE AT THE TITANIUM DIOXIDE / WATER INTERFACE. The decolorization and degradation of direct red 23 azo dye have been investigated in aqueous suspension of titanium dioxide under artificial irradiation. The effects of some operational parameters such as azo dye concentration, catalyst loading, and solution pH were investigated at 30.0 °C and optimized values were obtained. The first-order kinetic model was used to discuss the results. The UV-Vis spectra changes showed that the azo dye sample, collected after 6 h irradiation, was 98% decolorized while the residual total carbon was 97.9% degraded, indicating simultaneous photodecolorization and degradation.Keywords: photocatalysis; diazo dye; titanium dioxide. INTRODUÇÃOA contaminação de águas naturais tem sido apontada como um dos maiores problemas da sociedade moderna. Dentro deste contexto, o setor têxtil apresenta especial destaque por utilizar grandes quantidades de água e por gerar grandes volumes de efluentes, os quais apresentam composição extremamente heterogênea 1 . Estes efluentes apresentam coloração intensa porque aproximadamente 20% da produção total de corantes são perdidos para o meio ambiente durante a etapa de tingimento das fibras 2 . Considerandose ainda que mais de 50% da produção mundial de corantes orgâni-cos sejam provenientes das indústrias têxteis, significa que se o tratamento não for adequado pode alterar o ecossistema, diminuindo a transparência da água e a penetração da radiação solar e, conseqüentemente, a atividade fotossintética e a solubilidade dos gases. Além disso, admite-se que o maior problema ambiental seja gerado pela utilização ampla de azo corante, de reconhecido efeito carcinogênico e mutagênico, já que representa cerca de 60% dos corantes consumidos atualmente no mundo 3 . O tratamento de efluentes têxteis tem sido realizado através da combinação de processos convencionais físicos, químicos e bioló-gicos, em virtude das características complexas e bio-resistentes 4 . No entanto, estes processos não são destrutivos, pois simplesmente transferem o composto orgânico do meio aquoso para outro meio causando poluição secundária. Devido às limitações dos processos convencionais para descoloração de efluentes têxteis, têm se buscado as tecnologias efetivas e economicamente viáveis para resolução desse impasse ambiental. Uma alternativa para reduzir os subprodutos e a cor desses efluentes são os Processos de Oxidação Avançados (POAs) que geralmente utilizam agentes oxidantes fortes e/ou catalisadores, como TiO 2 , na presença ou não de radiação para gerar radical hidroxila HO•. Este radical por ser altamente reativo é capaz de mineralizar as substâncias orgânicas presentes nos efluentes industriais 5 . Dentre os processos que produzem radical hidroxila, a fotocatálise heterogênea tem se mostrado no decorrer das duas úl-timas décadas como um dos métodos mais promissores na destruição d...

A simple, low cost sensor was developed for the voltammetric determination of hydrogen peroxide in mouthwash and dental whitening gel based on multi-walled carbon nanotubes incorporated with hemin. The sensor showed electrocatalytic activity toward the reduction of hydrogen peroxide in 0.05 mol L −1 Tris-HCl buffer solution (pH 7.0) using cyclic voltammetry. The optimum composition of paste was 20:10:70 % (m/m/m (multi-walled carbon nanotubes:hemin:mineral oil). A linear plot of the square root of scan rate vs. cathodic peak current showed that reduction of hydrogen peroxide is diffusion controlled. Using linear sweep voltammetry, the analytical curve ranged from 0.2 up to 1.4 mmol L −1 (r = 0 9996) with a sensitivity of 3 62 × 10 −2 mA mol −1 L. The limits of detection and quantification were found to be 12 5 mol L −1 and 41 7 mol L −1 , respectively. The developed method was applied for hydrogen peroxide determination in dental formulations. The results were compared with a volumetric method as a reference technique. No significant differences at the 95% level (paired student t test) were observed, thus demonstrating the accuracy of the sensor for the analysis of real samples.