Determination of Pb, Cu and Fe in ethanol fuel samples by high-resolution continuum source electrothermal atomic absorption spectrometry by exploring a combination of sequential and simultaneous strategies

Abstract

An analytical method was developed for the sequential and simultaneous determination of Pb, Cu and Fe in ethanol fuel samples using high-resolution continuum source electrothermal atomic absorption spectrometry (HR-CS ET AAS). The sample preparation consisted in a simple dilution of the ethanol fuel with 0.1molL−1 HNO3. First, Pb was determined at 217.0005nm, using pyrolysis and atomization temperatures of 850°C and 1400°C, respectively. Sequentially, after changing the wavelength, Cu (216.5090nm) and Fe (216.4550nm) were determined simultaneously from a single sample aliquot, using an atomization temperature of 2400°C (Cu and Fe). These instrumental determination steps were performed in approximately 3min. Pd/Mg and NH4H2PO4 solutions were examined as chemical modifiers; however, the best signals were obtained without the use of modifiers. Under the optimized conditions of pyrolysis and atomization temperature, acidity and sample volume, the method allowed the sequential and simultaneous determination of Pb, Cu and Fe in ethanol fuel, and the limits of detection and quantification were 0.94 and 2.84μgkg−1 for Pb, 3.06 and 9.35μgkg−1 for Cu and 136.0 and 408.0μgkg−1 for Fe, respectively. The measurement precisions, expressed as the relative standard deviation (n=10; 12.8μgkg−1 for Pb, 63.8μgkg−1 for Cu and 3400μgkg−1 for Fe) were 7, 3 and 4% for Pb, Cu and Fe, respectively. The maximum ethanol content and acidity of the solution were investigated, and an ethanol concentration of 80% (v v−1) with samples diluted with 0.1molL−1 HNO3 was selected prior to determination by HR-CS ET AAS. Addition and recovery tests were performed, and the results ranged from 82 to 111% for Pb, 84 to 109% for Fe and 96 a 113% for Cu. The matrix effect was evaluated by comparing the calibration curves prepared in alcohol and aqueous media, and the results indicated that external calibration was possible. The proposed method was applied for the determination of Pb, Fe and Cu in ethanol fuel samples, and the maximum concentrations were found to be 2.04μgkg−1 for Pb, 24.3μgkg−1 for Cu and 2.465μgkg−1 for Fe.