Selenium preconcentration for its electrothermal atomic absorption spectrometric determination in biological tissues, such as food samples, is described. The method is applicable to matrices containing 0.05-1 mg kg 21 Se, like fish, meat, and flour. After a closed nitric acid digestion procedure, an aliquot of the sample is diluted with 0.2% v/v HNO 3 , diethyldithiophosphate solution is added and the complex formed is loaded on a minicolumn containing 30 mg of SiO 2-C 18 , using a peristaltic pump. The complex, eluted with ethanol, is collected into a cuvette for the determination of selenium. A calibration curve is made from selenium(IV) solutions, prepared in 0.2% v/v HNO 3. In order to minimize diethyldithiophosphate interference, a chemical modifier is used, chosen after comparison among Rh, Pd, Ir and Ni, and Rh proved to be the best. The furnace program can include a pyrolysis step at 1000 uC or, alternatively, omit it, skipping from a drying step to the atomization. A typical analytical curve goes up to 4 ng mL 21 Se. An enrichment factor of 65 is possible, taking 6 min for each preconcentration step. Good results were obtained for several certified reference materials. The entire procedure, including the digestion, can proceed rapidly, because there is no need for a pre-reduction step, coprecipitation or a lengthy solvent extraction.
Reference methods for determining lead in food are usually time-consuming. This paper reports a straightforward procedure using electrothermal atomic absorption spectrometry (ETAAS), to determine lead (Pb) in fat-free sweets. Several chemical modifiers were examined and results showed that it is not necessary to digest the samples, when a rhodium (Rh) modifier was used. The samples were dissolved in nitric acid and the determination of Pb was performed by ETAAS, using Rh chemical modifier at a pyrolysis temperature of 900 degrees C and an atomization temperature of 1,500 degrees C. No ashing step was employed and aqueous standards were used, in the range 2-10 microg l(-1). The limit of quantification was 0.095 mg kg(-1), and the accuracy of the method was verified by analysing certified reference materials.
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