Fractionation and speciation of nickel and vanadium in crude oils by size exclusion chromatography-ICP MS and normal phase HPLC-ICP MS

Abstract

The coupling of size exclusion chromatography (SEC) and normal phase (NP) HPLC using entirely organic mobile phases (tetrahydrofuran, xylene) with inductively coupled plasma mass spectrometry (ICP MS) were developed and investigated for the molecular distribution of nickel and vanadium in crude oils. The metal species were fractionated by SEC using three columns in series with the increasing porosity (100, 1000 and 100000 A) covering the molecular mass range (in eq. polystyrene) between 300 and 2 Â 10 6 Da. The resolution achieved allowed the discrimination of at least three classes of Ni and V species with varying proportions of the metals as a function of the origin of crude oil, crude oil fraction (asphaltene, maltene) and dilution factor. Normal phase HPLC-ICP MS allowed the separation of the porphyrin-type fraction as well as separation of the remaining species into three distinct fractions. The metal species in the SEC fractions were found to be sufficiently stable to be collected and preconcentrated to allow the development of a bidimensional chromatography SEC-NP-HPLC-ICPMS for the probing of the metal distribution in crude oils in terms of molecular weight and polarity.

Development of a chromatographic methodology for the separation and quantification of V, Ni and S compounds in petroleum products

“…Caumette et al [20,21] developed a methodology to separate and speciate Ni and V compounds in crude oils.The resolution achieved using their technique allowed the discrimination of at least three classes of Ni and V species containing varying proportions of the metals as a function of the origin of the crude oil, the crude oil fraction (asphaltenes vs.maltenes) and the dilution factor. Even more recently, another group Wandekoken et all [22] developed a methodology for separation of organic vanadyl 5 compounds in crude oil using fractionation by preparative liquid chromatography using as eluent different mobile phases, in their results all the V is linked to porphyrin structure, discarding the existence of non porphyrinics Vanadium compounds and a similar distribution of the vanadyl porphyrins between polar and non polar fractions.…”

Asphaltenes: Separations, structural analysis and applications

“…Inductively coupled plasma MS (ICP MS) has become a popular detector in liquid chromatography study of asphaltenes, especially for its endurance with absolutely tetrahydrofuran (THF) and xylene [124] . For example, SEC-ICP MS demonstrated metal (Ni, V) distributions with different proportions in asphaltene fractions.…”

“…NP HPLC-ICP MS found that Ni and V mostly appeared in non-porphyrin congeners with different polarities. SEC connected with NP HPLC served as an improved prior purification of metal analysis by MS [124] . Besides, argentation chromatography was used to compare asphaltene PAH with or without heteroatoms (N, O, S) and monitor the change of molecular components and achieve isomers separation with APPI /APCI MS [138] .…”

Different approaches of crude oil mineralisation for trace metal analysis by ICPMS

“…Hyphenated techniques, like ETV with ICPMS [10], LA with ICPMS [11][12][13] or the use of emulsion [14,15] offer other alternatives for direct injection. In addition, speciation analysis based on HPLC-ICP [16] or GC-ICP [17,18] coupling has recently received special attention.…”