Investigation of the potential of the ICP-MS/MS for total and speciation analysis in petroleum fractions

Abstract

The capability of inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) to achieve total concentration and speciation using direct injection of petroleum products after solvent dilution for severely interfered isotopes was demonstrated here with different applications cases. For the direct determination of heavy elements (Z > 70) in organic matrices, the ICP-MS/MS was less sensitive than the ICP-HRMS. For light elements (Z < 40), the sensitivity was similar or better using ICP-MS/MS and for interfered elements (Si, S, Ca, Fe), the use of the two quadrupoles combined to the octopole reaction/collision cell (ORC) with He, O2 or H2 gave similar or better detection limits (LOD) than the ICP-HRMS in medium resolution. Comparable or better sensitivity were obtained replacing the 1.5 mm by the 1 mm injector diameter and especially for lighter elements (Z < 30) using the ICP-MS/MS. LOD in xylene were ranging from 0.004 μg/kg (V) to 0.9 μg/kg (Al) and appeared in the lowest values published in the literature using ICP-MS/MS in hydrocarbons. To demonstrate the performance of the ICP-MS/MS using direct injection of petroleum products after dilution in hydrocarbon solvent, three application cases were presented.Sulfur at very low levels in reformates was successfully monitored in oxygen mode using the oxide ion (32S → 48SO). The background equivalent concentration (BEC) origin was attributed to solvent contamination by sulfur and was confirmed by ultra-violet fluorescence (UVF) method. Using H2 for Ni (58Ni → 58Ni) and O2 for V (51V → 67VO) as reactant gas, the direct injection ICP-MS/MS method easily confirmed Ni and V concentrations measured using wavelength dispersive X-rays fluorescence (WDXRF) and allowed the determination of 14 elements in the asphaltene fraction, with concentrations ranging from 0.3 mg/kg (Al and Pb) to 37.4 mg/kg for Fe.For speciation of Ni, V and S, gel permeation chromatography (GPC) hyphenated to ICP-MS/MS is particularly powerful using O2 (2.5 mL/min) both for vacuum residue and hydrotreated (HDT) vacuum residue. Contrary to GPC-ICP-HRMS where two injections of sample were required (medium resolution for S and V and low resolution for Ni), GPC-ICP-MS/MS easily allowed the acquisition of the 3 elements in one mode during the same run and considerably reduce the analysis cost and time. Both for total and speciation analysis, the direct injection of petroleum products after solvent dilution ICP-MS/MS method is a significant advantage and appealing in high-volume petroleum laboratories.