Direct and simultaneous determination of Cr and Fe in crude oil using high-resolution continuum source graphite furnace atomic absorption spectrometry

A simple, fast and sensitive direct method for the simultaneous determination of Cr and Fe in crude oil samples is proposed using high-resolution continuum source graphite furnace atomic absorption spectrometry. No sample preparation is used except for a 10-minute homogenization in an ultrasonic bath. Aliquots of 0.1-4 mg of the samples are weighed onto solid sampling platforms and analyzed directly using aqueous standards for calibration. The simultaneous determination was possible because there is a secondary Fe line at 358.120 nm in the vicinity of the most sensitive Cr line at 357.868 nm, and both absorption lines were within the wavelength interval covered by the linear charge-coupled device array detector. It has also been of advantage that the sensitivity ratio between the two analytical lines corresponded roughly to the concentration ratio of the two elements found in crude oil, and that both analytes have very similar volatility, so that no compromises had to be made regarding pyrolysis and atomization temperatures. Two oil reference materials have been analyzed and the results were in agreement with the certified or reported values. Characteristic masses of 3.6 pg and 0.5 ng were obtained for Cr and Fe, respectively. The limits of detection (3 sigma, n = 10) were 1 mu g kg(-1) for Cr and 0.6 mg kg(-1) for Fe, and the precision, expressed as the relative standard deviation, ranged from 4 to 20%, which is often acceptable for a rapid direct analytical procedure. Five crude oils samples were analyzed. (C) 2009 Elsevier B.V. All rights reserved.