Simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by GFAAS

Abstract

A method has been developed for the simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by graphite furnace atomic absorption spectrometry (GFAAS) using a transversely heated graphite atomizer(THGA) with longitudinal Zeemaneffect background correction. The thermal behavior of analytes during the pyrolysis and atomization stages using the mixture Pd(NO3)2 + Mg(NO3)2 as the chemical modifier was investigated in 0.028 mol L-1HNO3, 0.14 mol L-1 HNO3, and dilutedethanol (1 + 1, v/v) containing different nitric acid concentrations. With 5 μg Pd + 3 μg Mg as the modifiers, pyrolysis and atomization temperatures of the heating program of the atomizer were fixed at 1200°C and 2200°C, respectively. For 20 μL of diluted sample (10 μL ethanol + 10 μL of 0.28 mol L-1 HNO3) dispensed into the graphite tube, analytical curves in the 2.0 - 50 μg L-1 Al, As, Cu, Fe, Mn, Ni ranges were established. The calculated characteristic masses were ∼ 37 pg Al, 73 pg As, 31 pg Cu, 16 pg Fe, 9 pg Mn, and 44 pg Ni, and the lifetime of the tube was around 250 firings. The limits of detection (LOD) based on integrated absorbance were 1.2 μg L-1 Al, 2.5 μg L-1 As, 0.22 μg L-1 Cu, 1.6 μg L-1 Fe, 0.20 μg L-1 Mn, 1.1 μg L-1 Ni. The relative standard deviations (n = 12) were ≤ 3%, ≤ 6%, ≤ 2%, ≤ 3.4%, ≤ 1.3%, and ≤ 2% for Al, As, Cu, Fe, Mn, and Ni, respectively. The recoveries of Al, As, Cu, Fe, Mn and Ni added to fuel ethanol samples varied from 77% to 112%, 92% to 114%, 104% to 113%, 73% to 116%, 91% to 122% and 93% to 116%, respectively. Accuracy was checked for Al, As, Cu, Fe, Mn, and Ni determination in 20 samples purchased at local gas stations in Araraquara city, Brazil. A paired t-test showed that the results were in agreement at the 95% confidence level with those obtained by single-element GFAAS.