Simultaneous Determination of Cadmium and Lead in Wine by Electrothermal Atomic Asborption Spectrocetry

摘要

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrotheraml atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l~(-1) NHO_3 and in 1+1 v/v diluted wine using mixtures of Pd(NO_3)_2 + Mg(NO_3)-2 and NH_4H_2PO_4 + Mg(NO_3)_2 as chemical modifiers. With 5 #mu#g Pd + 3 #mu#g Mg as the modifiers and a two-step pyrolysis (10 s at 400 deg C and 10 s at 600 deg C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 #mu#l of sample (wine + 0.056 mol l~(-1) NHO_3, 1+1, v/v) dispensed into the raphite tube, analytical curves in the 0.10-1.0 #mu#g l~(-1) Cd and 5.0-50 #mu#g l~(-1) Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 #mu#g l~(-1) for Cd, 0.8 #mu#g l~(-1) for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 #mu#g l~(-1) and for Pb at 500 #mu#g l~(-1). The relative standard deviations (n = 12) were typically < 8% for Cd and < 6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreemetn at the 95% confidence level.