High Precision Determination of Metal Elements in Crude Oils by ICP-MS/ICP-OES
Weihang Yang¹, Yongjun Gao¹, and John F. Casey¹
¹University of Houston
In order to eliminate complex spectral interference and polyatomic interference from organic matrix of crude oil, oil sample was decomposed into aqueous solution for trace metal analysis with ICP-OES and ICP-MS. We have studied two sample preparation techniques: dry combustion with Parr oxygen bomb and wet digestion with high pressure Parr acid digestion bomb. The validity of method has been tested with the Conostan multi-element metallo-organic standard of S21+Be+K+Li+Sb (100 ppm). For dry combustion, sample was combusted in a quartz crucible within a quartz liner in a Parr oxygen bomb in water bath with 8N HNO3 as absorbing solution at the bottom of liner, followed by digestion with concentrated HCl, HNO3 and HF, drying, sample pick up and dilution. The results show that the recovery of all the elements is lower than 80%, and even lower than 20% for B, Si, Zn, Ag, Sn and Sb. The repeatability of Li, Na, P, K, Ca, V, Cu, Zn, Mo and Pb in term of relative standard deviation (RSD) ranges from 1.5-4.9%, and Mg, Mn, Fe, Ni, Cd and Sn is 5.5-9.3%. Be, Al, Ti, Cr, Ag, Sb and Ba is 13.7-21.6%. B and Si have RSD of 92.9% and -22.9%, respectively. We have proved that the elemental losses were not caused by incomplete combustion, incomplete solution transfer, conglutination of samples to the wall of the bomb, or volatilization of the analytes. The repeatability of Li, Na, Mg, P, K, Ca, V, Cu, Zn, Mo, Cd and Pb is good, and the RSD is 1.5-9.2%. Wet digestion was conducted by adding a sample and concentrated HCl and HNO3 into a liner, followed by bomb assembly. The bomb was put into an oven and heated at 160°C for 11 h. After cooling, the digested sample solution was transferred into a Teflon beaker to be dried, followed by sample pick up. The results show that the recovery of Li, Al, Ca, Ni, Be, Cr, Fe, Mn, Na, V, Ba, K, Mg and Mo is higher than 95%, and Cd, Cu, Pb, Sb and Ti is around 95%. Zn is 92.6-94.5%. The repeatability of these analytes with RSD ranges from 0.7-2.6%. Ag has both of poor recovery of 8.2-26.8% and repeatability with RSD of 45.6%, while Si has poor recovery of 60.8-75.9% and relatively good repeatability with RSD of 8.2%. Wet digestion is more effective than dry combustion in recovery. Concentration of Li, Be, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Mo, Cd, Sb, Ba, Pb and maybe Ag in 28 crude oil samples collected from Angola, North Asia and Texas, US will be presented.
AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014