Simultaneous determination of Cr, Fe, Ni and V in crude oil by emulsion sampling graphite furnace atomic absorption spectrometry

Abstract

In this work a simple and reliable method for the simultaneous determination of Cr, Fe, Ni and V in crude oil, using emulsion sampling graphite furnace atomic absorption spectrometry is proposed. Under the best conditions, sample masses around 50 mg were weighed in polypropylene tubes and emulsified in a mixture of 0.5% (v v⁻¹) hexane + 6% (m v⁻¹) Triton X-100^®. Considering the compromised conditions, the pyrolysis an atomization temperatures for the simultaneous determination of Cr, Fe, Ni and V were 1400 °C and 2500 °C, respectively. Aliquots of 20 μL of reference solution and sample emulsion were co-injected into the graphite tube with 10 μL of 1.0 g L⁻¹Mg(NO₃)₂ as chemical modifier. The detection limits (n = 10, 3σ) and characteristic masses were, respectively: 0.07 μg g⁻¹ and 19 pg for Cr; 2.15 μg g⁻¹ and 31 pg for Fe; 1.25 μg g⁻¹ and 44 pg for Ni; and 1.15 μg g⁻¹ and 149 pg for V. The reliability of the proposed method was checked by fuel oil Standard Reference Material (SRMTriton X-100^®1634c – NIST) analysis. The concentrations found presented no statistical differences compared to the certified values at 95% confidence level.