RESUMO

The applicability of thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was evaluated for direct determination of Cu, Cd and Pb in wines and grape juices. The developed procedure does not require preliminary acid digestion of the samples. The optimum conditions for determination of Cu, Cd and Pb in wines were studied and the performance was compared to those typically obtained by flame atomic absorption spectrometry (FAAS). A sample volume of 150 microL was introduced into a heated nickel tube at a flow rate of 0.54 mLmin(-1) and 0.14 molL(-1) HNO(3) was used as sample carrier flowing at 2.5 mLmin(-1) for determining all analytes. The effect of ethanol concentrations on Cu, Cd and Pb absorbance signals were studied. All determinations were carried out by adopting optimized conditions and quantification was based on the standard additions method. Limits of detection (LOD) of 12.9, 1.8 and 5.3 microgL(-1) (n=14) for Cu, Cd and Pb, respectively, were obtained for wine samples (3sigma(blank)/slope, n=14). Relative standard deviations (R.S.D., %) of 2.7, 2.1 and 2.6 for Cu, Cd and Pb, were obtained (n=6) for wine samples. The values determined for grape juice samples were similar to these ones. The analytical throughput was 45 determinations h(-1) and accuracy was checked by addition-recovery experiments.

Assuntos

Bebidas/análise , Cádmio/análise , Cobre/análise , Chumbo/análise , Espectrofotometria Atômica/métodos , Vitis/química , Vinho/análise , Absorção , Calibragem , Custos e Análise de Custo , Etanol/química , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Espectrofotometria Atômica/economia , Fatores de Tempo

RESUMO

Three platinum group elements (Pd, Ir and Rh) both in solution and in pre-reduced form, and also combined with Mg(NO(3))(2) or ascorbic acid, were assessed as possible chemical modifiers on the atomization of As in digest solutions of seafood matrices (clam and fish tissue) by tungsten coil electrothermal atomic absorption spectrometry (TCA-AAS) and compared without a modifier. Of 28 modifier alternatives in study including single form and binary mixtures, and based on maximum pyrolysis temperature without significant As loss and best As absorbance sensitivity during atomization, three modifiers: Rh (0.5microg), Ir (1.0microg) and Rh (0.5microg)+ascorbic acid (0.5microg), at optimum amounts were pre-selected and compared. The definitive modifier (rhodium (0.5microg)) was selected by variance analysis. The mean within-day repeatability was 3% in consecutive measurements (25-300microg l(-1)) (three cycles, each of n=6) and showed good short-term stability of the absorbance measurements. The mean reproducibility was 4% (n=18 in a 3-day period) and the detection limit (3sigma(blank)/slope) was 42pg (n=16). Quantitation was by standard additions to compensate for matrix effects not corrected by the modifier. Three sample digestion procedures were compared in fish and clam tissue samples: microwave acid digestion alone (A) or combined with the addition of 2% (m/v) K(2)S(2)O(8) solution followed either by UV photo-oxidation (B) or re-digestion in a thermal block (C). The accuracy was established by determination of As in certified reference material of dogfish muscle (DORM-2). Procedures B and C showed good recoveries (102% (n=4) and 103% (n=7), respectively), whereas procedure A was not quantitative (85%). The methodology is simple, fast, reliable, of low cost and was applied to the determination of total As in lyophilized samples of clam and fish collected in the Chilean coast.

RESUMO

A multi-reversed flow system software-assisted was developed for improvement of sensitivity in flow analysis. The performance of the flow system proposed was evaluated by using as a model the conventional Griess' colorimetric reaction for determination of nitrite in waters. The manifold incorporated three 3-way solenoid valves, a relay box solenoid actuated, a peristaltic pump, and a photometric detector. A tailored software was designed and written in Visual Basic 6.0 which allows full control of all flow system components and simultaneous acquisition and processing of the data. The sensitivity measured as the slope of the calibration curve was improved 2.5- and 1.4-fold regarding those obtained by continuous- and stopped-flow systems, respectively. Other valuable features such as analytical throughput of 55 determinations per hour, limit of detection of 5mugL(-1) (3sigma(blank)/slope), relative standard deviation<2% (n=8), and a linear dynamic range up to 1800mugL(-1) were also achieved.

RESUMO

The behavior of selenium in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was studied and the developed procedure was applied for selenium determination in biological materials after microwave-assisted sample digestion. A sample volume of 600muL was introduced into the hot metallic Ni tube at a flow rate of 0.4mLmin(-1) using water as carrier. The limit of detection obtained for Se was 8.7mugL(-1) (3s(blank)/slope, n=10), which is 95-fold better than that typically obtained using FAAS. The applicability of the TS-FF-AAS procedure was evaluated for selenium determination in biological materials. Certified reference materials of pig kidney (BCR 186) and mussel (GBW 08571) were analyzed and a t-test had not shown any statistically significant difference at a 95% confidence level between determined and certified values for both materials. The procedure was successfully applied for determination of Se in pig kidney and shellfish. It was demonstrated that TS-FF-AAS improved the performance of FAAS (flame atomic absorption spectrometry) for determination of Se.