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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.

Biofuel quality control involves the determination of metal and metalloid content.

The size distributions of sulfur (S), vanadium (V), and nickel (Ni) compounds in four crude oils, two residues, and their saturate, aromatic, resin, and asphaltene (SARA) fractions were determined using gel permeation chromatography (GPC) coupled to inductively coupled plasma high-resolution mass spectrometry (ICP HR MS). The results show trimodal distributions of V, Ni, and S compounds in the crude oils and residues. V and Ni compounds are present in both resins and asphaltenes. Trimodal distributions are clearly apparent in the resins but not apparent in the asphaltenes. In the latter, the predominant compounds have a high molecular weight (HMW), even when the solution of asphaltenes is diluted by 40000-fold. In the resins, compounds with a medium molecular weight (MMW) were expected; however, HMW compounds were observed, indicating that nanoaggregates or large molecules exist in both the asphaltenes and resins. Low-molecular-weight (LMW) compounds are predominantly present in the resins and do not represent more than 22% of V and Ni present in crude oil. These compounds appear to have molecular weights similar to simple metalloporphyrins.

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