M. G. R. Vale, M. M. Silva, I. C. F. Damin, et al. Determination of volatile and non-volatile nickel and vanadium com-pounds in crude oil using electrothermal atomic absorption spectrome-try after oil fractionation into saturates, aromatics, resins and asphalte-nes. Talanta, 2008, 74(5): 1385-1391.