HIGH PRECISION DETERMINATION OF TRACE ELEMENTS IN CRUDE OILS BY USING INDUCTIVELY COUPLED PLASMA-OPTICAL EMISSION SPECTROMETRY AND INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY

This study attempts to develop a method to precisely analyze multiple trace metal elements in crude oils by ICP-OES/ICP-MS. To eliminate spectral and polyatomic interferences caused by complex organic matrix of crude oils, oil samples were decomposed into aqueous solutions. We have studied two sample preparation techniques: combustion under high pressure and wet digestion under high pressure and temperature. A 100 ppm (wt./wt.) multi-element organo-metallic standard from Conostan, extended S21, was applied as the test standard in combustion and acid digestion. The results of combustion by ICP-OES have shown that the best recovery is about 85% for Na. For the results of wet digestion by ICP-OES, the recoveries of Al, Ba, Be, Ca, Cd, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Sb, Sn, and V are better than 95%, and Pb, Ti, and Zn are better than 93%. The developed method was applied to test NIST 8505 for 47 trace elements aiming to develop it into a potential crude oil standard for multiple metal elements. Accurate concentrations of 46 elements together with V in NIST 8505 have been constrained, among them, Al, Ba, Co, Cu, Mg, Mn, Ni, and Sr have been tested by both ICP-OES/ICP-MS which showed a good agreement within analytical error range. 26 crude oil samples from Permian Basin and Fort Worth Basin, Texas, U.S., Angola, Timan Pechora Basin in Russia, and Central Sumatra Basin in Indonesia, were also tested by the developed working method for 47 trace elements. Our results indicated that the multiple trace metal contents in crude oils can be applied as a powerful tool to both upstream and downstream investigations and refining processes in the petroleum industry.