Challenges to identification, characterisation and determination of element species in crude and residual oils, oil fractions, natural gas and gas condensates, and related products are presented. The principal elements of concern include vanadium, nickel, sulfur, mercury and arsenic. The state-of-the-art of analytical methods available for element speciation in petroleum-related matrices is discussed with particular attention given to chromatography with plasma source atomic spectrometric detection. Methods for fractionation of metal species prior to chromatography are critically reviewed. Analysis for metal species by gas (GC) and liquid chromatography (LC) using different separation mechanisms (size-exclusion, adsorption, ion-exchange, reversed and normal-phase) and element selective detection are discussed. The potential and limitations of LC-ICP AES, LC-ICP MS, GC-MIP AES and GC-ICP MS are highlighted in the context of techniques allowing a direct insight into the metal coordination in petroleum-related samples, such as X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) and molecular mass spectrometry (using laser desorption, electrospray and chemical ionization).

Se is an essential micronutrient required for normal growth, development and antioxidant defence. The objective of the present study was to assess the impact of dietary Se sources and levels on the antioxidant status of rainbow trout (Oncorhynchus mykiss) fry. First-feeding fry (initial body weight: 91 mg) were fed either a plant- or fishmeal-based diet containing 0·5 or 1·2 mg Se/kg diet supplemented or not with 0·3 mg Se/kg diet supplied as Se-enriched yeast or sodium selenite for 12 weeks at 17°C. Growth and survival of rainbow trout fry were not significantly affected by dietary Se sources and levels. Whole-body Se was raised by both Se sources and to a greater extent by Se-yeast. The reduced:oxidised glutathione ratio was raised by Se-yeast, whereas other lipid peroxidation markers were not affected by dietary Se. Whole-body Se-dependent glutathione peroxidase (GPX) activity was enhanced in fish fed Se-yeast compared to fish fed sodium selenite or non-supplemented diets. Activity and gene expression of this enzyme as well as gene expression of selenoprotein P (SelP) were reduced in fish fed the non-supplemented plant-based diet. Catalase, glutamate–cysteine ligase and nuclear factor-erythroid 2-related factor 2 (Nrf2) gene expressions were reduced by Se-yeast. These results suggest the necessity to supplement plant-based diets with Se for rainbow trout fry, and highlight the superiority of organic form of Se to fulfil the dietary Se requirement and sustain the antioxidant status of fish. GPX and SelP expression proved to be good markers of Se status in fish.

Speciation of nickel was investigated in a hyperaccumulator tree, Sebertia acuminata, by liquid chromatography (LC) with parallel ICP MS and electrospray MS-MS detection. The latex of the tree was leached with water. Two separation mechanisms, size-exclusion (SEC) and capillary zone electrophoresis (CZE), were investigated for the separation of Ni-complexes. A preparative scale SEC allowed the isolation of six stable nickel species. A nickel complex with M_r 360 was identified by ES MS. The collision induced fragmentation (CID) of the m/z 360 ion suggested the presence of three carboxylic and one amino groups, and allowed the identification of a Ni-complex with nicotianamine. A modification of the SEC column with Ni²⁺ ions allowed the isolation of a fraction containing nickel citrate. Quantification of the species showed that in the water extract of the latex 99.4% of the nickel is complexed by citrate and 0.3% by nicotianamine.

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 Å) covering the molecular mass range (in eq. polystyrene) between 300 and 2 × 10⁶ 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.