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

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[registered sign]. Considering the compromised conditions, the pyrolysis an atomization temperatures for the simultaneous determination of Cr, Fe, Ni and V were 1400 [degree]C and 2500 [degree]C, respectively. Aliquots of 20 [small mu ]L of reference solution and sample emulsion were co-injected into the graphite tube with 10 [small mu ]L of 1.0 g L-1 Mg(NO3)2 as chemical modifier. The detection limits (n = 10, 3[sigma]) and characteristic masses were, respectively: 0.07 [small mu ]g g-1 and 19 pg for Cr; 2.15 [small mu ]g g-1 and 31 pg for Fe; 1.25 [small mu ]g g-1 and 44 pg for Ni; and 1.15 [small mu ]g g-1 and 149 pg for V. The reliability of the proposed method was checked by fuel oil Standard Reference Material (SRMTriton X-100[registered sign] 1634c - NIST) analysis. The concentrations found presented no statistical differences compared to the certified values at 95% confidence level.