The size distribution of sulfur, vanadium, and nickel was determined for four crude oils and their distillation cuts using gel permeation chromatography (GPC) coupled to inductively coupled plasma high-resolution mass spectrometry (ICP HR MS). The results show a trimodal distribution of vanadium and nickel compounds in the crude oils, the atmospheric residues, and the vacuum residues and, for sulfur compounds, either a mono- or bimodal distribution depending upon the distillation cut considered. A correlation exists between the sulfur fraction retention times and the temperature cuts of the distillation for a temperature below 560 °C and also between the viscosity of the crude oils and the proportion of trapped sulfur compounds in a higher boiling temperature fraction. The thermic treatment applied for the distillation increases the aggregation of low- and medium-molecular-weight compounds of vanadium and nickel into higher molecular weight aggregates between the crude oil on the one hand and the atmospheric residue and vacuum residue on the other hand, especially when the crude oil has a high total sulfur content.

A novel nebulizer (nDS-200) working at sample uptake rates of less than 500 nL min(-1) was developed for a sheathless interfacing of nanoHPLC (75-microm column i.d.) with ICPMS. It was based on a hollow fused-silica needle of which the tip (i.d. 10 microm, o.d. 20 microm) centered in a 254-microm-i.d. sapphire orifice. The nebulizer, equipped with a 3-cm(3) drain-free vaporization chamber, enabled a stable introduction into an ICP of aqueous mobile phases containing up to 95% acetonitrile at eluent flow rates between 50 and 450 nL min(-1). The low dead volume of the interface resulted in a peak width of 1.3 s (at half-height) and the entirely preserved chromatographic resolution. An example application of the coupling to the analysis of a tryptic digest of a SIP18 protein containing two to nine selenomethionine residues was described. The absolute detection limit was 25 fg (80Se), which allowed the detection of low-abundant selenopeptides at the femtomole level. In contrast to electrospray MS, the ICPMS detection in nanoHPLC is unaffected by the coeluting matrix and concomitant compounds and offers an elegant method for the detection and quantification of minor heteroelement-containing species prior to or in parallel with ESI MS analysis.

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.

A novel generic approach based on precolumn isotope dilution nanoHPLC-ICPMS analysis was developed for the accurate absolute quantification of sulfur-containing peptides. A 34S-labeled, species-unspecific sulfur spike (sulfate), noninteracting with analyte peptides under the optimized HPLC condition, was added directly to the chromatographic eluents. Thus a generic sulfur standard permanently present during analysis was used for peptide quantification. Interference-free detection of the 32S and 34S isotopes in ICPMS was achieved by eliminating O2+ ions in a collision cell using Xe gas at 130 microL min-1. The detection limit for sulfur was 45 microg L-1 which corresponded to 1-2 pmol of individual peptides. The method was validated by the analysis of a standard peptide solution showing high accuracy (recovery 103%) and good precision (RSD 2.1%). The combination of nanoHPLC-ICP IDMS with nanoHPLC-ESI MS/MS allowed the precise quantification and identification of sulfur-containing peptides in tryptic digests of human serum albumin and salt-induced yeast protein (SIP18) at the picomole level.

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Gel Permeation Chromatography Inductively Coupled Plasma High Resolution Mass Spectrometry (GPC ICP HR MS) was used for the understanding of the evolution of two crude oil cut samples after their dilution. We firstly studied different method parameters in order to compare two GPC procedures already published (flow rate, column set, presence or not of the THF stabilizer). Thus, the principal parameters affecting the molecular size distribution and its evolution were demonstrated. The column set and flow rate can affect drastically the molecular size distribution of the sample. Moreover an evolution of the size distribution of the complexes of vanadium, nickel and sulfur into higher molecular weight compounds was observed over time.The study led to the recommendation of the sample preparation to the same day of the analysis in order to obtain reproducible data.

Recent advances in instrumentation for high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) have enabled access to ∼70 000 unique molecular formulas in broadband mass spectral characterization of unfractionated/whole asphaltenes. The results accumulated over a decade highlight the need for an asphaltene molecular model that acknowledges the coexistence of (1) monofunctional and polyfunctional species; (2) island and archipelago structural motifs; and (3) heteroatom-depleted/highly aromatic compounds, as well as atypical species with low aromaticity but increased heteroatom content. Collectively, results from FT-ICR MS, preparatory-scale separations (extrography/interfacial material), gel permeation chromatography, precipitation behavior in heptane:toluene, thermal decomposition, and aggregate microstructure by atomic force microscopy (among other techniques), suggest that the strong aggregation of asphaltenes results from the synergy between several intermolecular forces: π-stacking, hydrogen bonding, London forces, and acid/base interactions. This review presents general features of asphaltene molecular composition reported over the past five decades. We focus on mass spectrometry characterization and expose the reasons why early results supported the dominance of single-core motifs. Then, the discussion shifts to recent advances in instrumentation for high-field FT-ICR MS, which have enabled the detection of thousands of species in asphaltene samples, whose molecular composition and fragmentation behavior in ultrahigh vacuum agree with the coexistence of single-core and multicore structural motifs. Furthermore, evidence that highlights the limitations of commercially available/custom-built ion sources and selective ionization effects is presented. Consequently, the limitations require separations (e.g., chromatography, extrography) to gain more-comprehensive molecular-level insights into the composition of these complex organic mixtures. The final sections present evidence for the role of aggregation in selective ionization and suggest that advanced characterization by both thermal desorption/decomposition and liquid chromatography with online FT-ICR MS detection can be employed to mitigate the effects of aggregation and provide unique insights in molecular composition/structure.

Polyolefin, including polypropylene (PP), constitutes an important class of materials. In particular, the recent interest in recycling plastic wastes necessitates their characterization as well as their degradation mechanism being understood. PP materials characterization by mass spectrometry, including polymer and additives parts, is not direct and generally involves a pyrolysis step to produce ionizable species. In this study, we extended the use of atmospheric solid analysis probe (ASAP) in combination with traveling wave ion mobility mass spectrometry (TWIM-MS) for the characterization of PP materials, including polymer as well as additives. Different commercial PP samples, from polymer standard to plastic item, were studied. The use of ASAP allow analysis to be done without any sample preparation, while TWIM-MS permitted a clear separation of polymer ions and additive signals. Several series of polymer pyrolysis residues, similar to those produced by classic pyrolysis, were obtained. Moreover, additive characterization has been done and supported by accurate mass measurements and tandem mass spectrometry experiments. Finally, this strategy put in evidence the role of additives in polymer degradation.