The concentration of Cu, Fe, Na, Ni, and V were determined in four heavy distillates from three heavy crude oils and one commercial crude oil by atomic absorption spectrophotometry. The distillates were extracted by DMF in order to estimate the porphyrinic (extract) and nonporphyrinic (residue) fractions of V and Ni contents. The V was distributed almost equally between the two types, while most of the Ni content was in the nonporphyrinic form. The asphaltene and resin fractions of the distillates were isolated and analyzed for their Ni and V contents. It appeared that about 90% of these metallic species of the distillates were concentrated in these two fractions, which in turn share these metallic compounds equally.
Nabila S. Zaki, Mahmood M. Barbooti, Sulafa S. Baha-Uddin, and Eman B. Hassan, "Determination of Trace Metals and Their Distribution in Heavy Crude Oil Distillates (350°C+) by Atomic Absorption Spectrophotometry," Appl. Spectrosc. 43, 1257-1259 (1989)