New Separation Approach for Asphaltene Investigation: Argentation Chromatography Coupled with Ultrahigh-Resolution Mass Spectrometry

Abstract

Argentation chromatography has been developed for the analysis and separation of asphaltenes. The separation is based on the interaction between the silver ions (Ag⁺) bonded to a silica gel surface and the π-systems of the polycondensed aromatic compounds, where the interactions can be different when heteroatoms (N, O, S) are present in the molecules. Online coupling of argentation chromatography and high-resolution mass spectrometry allows fast and detailed analysis of the separation of crude oil asphaltenes. Highly condensed aromatic compounds possessing a high degree of unsaturation can be successfully separated using a mixture of toluene and chloroform (7:3 v/v) as mobile phase and dimethyl sulfoxide as competitive ligand for elution of asphaltene compounds with double bond equivalents (DBE) of up to 40. Making use of the different structural features of the components, it is possible to separate isomeric compounds that interact with different strengths with the stationary phase. The composition of mobile phase plays a significant role in separation efficiency

Compositional Trends for Total Vanadium Content and Vanadyl Porphyrins in Gel Permeation Chromatography Fractions Reveal Correlations between Asphaltene Aggregation and Ion Production Efficiency in Atmospheric Pressure Photoionization

“…Asphaltenes comprise arguably the most challenging and complex, naturally occurring mixture, and their importance to upstream production and downstream oil processing have triggered scientific interest for over 50 years. − Their definition as a solubility class, that is, n -heptane-insoluble/toluene-soluble, instead of a specific chemical/structural family, such as saturates, mono-aromatics, or vanadyl porphyrins, and associated complexity have motivated instrumentation advances in analytical chemistry, in particular, atomic force microscopy (AFM), , and high-magnetic field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). − …”

A Detailed Look at the Saturate Fractions of Different Crude Oils Using Direct Analysis by Ultrahigh Resolution Mass Spectrometry (UHRMS)

“…Crude oils for this study were selected from three different origins: A light oil from East Asia, a medium oil of Arabic origin and a heavier oil from Eurasia. A total of 6 g of each oil was collected and the asphaltenes were separated using a modified IP-143 method, which is described in detail elsewhere [26,28]. Of the remaining maltenes from each oil, 1 g was mixed with the silica sorbent (Silicalgel 60, 40-63 µm, Merck KGaA, Darmstadt, Germany) which later was loaded on an individual pre-column (75 mm × 12 mm).…”

“…In this study, saturate fractions of three different oils were analyzed by ultrahigh resolution mass spectrometry after direct infusion. One on the known challenges in any MS analysis is the discrimination and suppression effects of some compounds, which might occur during ionization [26,27]. Therefore, in order to get a more in depth knowledge about the chemical characteristics of the saturate fraction, the samples were analyzed using three different atmospheric pressure ionization (API) methods: Electrospray ionization (ESI), which is primarily used for the analysis of large, polar, heteroatom containing compounds [28][29][30][31]; atmospheric pressure chemical ionization (APCI), which is known to be suitable for the analysis of small to moderately large size non-polar molecules (e.g., saturated or partially unsaturated compounds) [32,33]; and atmospheric pressure photoionization (APPI), which is reported as an optimal ionization method for the investigation of aromatic petroleum hydrocarbons and the sulfur containing species in petroleum [34][35][36].…”

Comparing Crude Oils with Different API Gravities on a Molecular Level Using Mass Spectrometric Analysis. Part 2: Resins and Asphaltenes

“…A simple scheme which has been used for decades to separate crude oil components into fractions of saturates, aromatics, resins and asphaltenes depending on their solubilities, is called SARA fractionation [5]. In SARA fractionation the initial step is the removal of asphaltenes using a nonpolar solvent, while the remaining fraction, named maltenes, is further separated into saturates, aromatics and resins [6]. Resin and asphaltene fractions constitute the most complex part because of a high abundance of heteroatoms (N, O and S).…”

“…The resin fraction represents the most polar compounds in crude oils which may include both hydrogen-rich and hydrogen-deficient molecules, i.e., a mixture of saturated and aromatic compounds [7]. Meanwhile, asphaltenes comprise hydrocarbons and components with high numbers of heteroatoms, which contain highly condensed aromatic rings substituted with aliphatic chains [6]. The asphaltenes are reported to be maturation products of the resins.…”