Simultaneous determination of Cu and Pb in fuel ethanol by graphite furnace AAS using tungsten permanent modifier with co-injection of Ir

A method has been developed for the simultaneous determination of Cu and Pb in ethanol fuel by GF AAS using a transversely heated graphite atomizer (THGA) with W permanent modifier and co-injection of Ir. Pyrolysis and atomization temperature curves were established in fuel ethanol medium (1 + 1; v/v) containing 1.0% (v/v) HNO3 and spiked with 20 mu g L-1 Cu and Pb. For 20 mu L of diluted sample (10 mu L ethanol + 10 mu L of 2.0 % (v/v) HNO3) dispensed into the graphite tube, analytical curves in the 5.0-25 mu g L-1 Cu and 10-50 mu g L-1 Pb ranges were established. The calculated characteristic masses were 18 pg for Cu and 36 pg for Pb. The limits of detection (LOD) based on integrated absorbance were 0.086 mu g L-1 and 2.47 mu g L-1 for Cu and Pb, respectively. The recoveries of the spiked samples varied from 93-103% (Cu) and 96-110% (Pb). The relative standard derivations (n = 12) were <= 0.5 Cu and <= 0.7 Pb. Accuracy was checked for Cu and Pb determination in 10 samples purchased at local gas stations in Brazil. The found concentrations varied from 8.0 to 47 mu g L-1 Cu. All the analyzed samples presented Pb contents below the limit of detection of this method. These amounts are considered acceptable for the Brazilian regulatory agency for hydrated fuel ethanol. (C) 2012 Elsevier Ltd. All rights reserved.