Optimized asphaltene separation by online coupling of size exclusion chromatography and ultrahigh resolution mass spectrometry

Abstract

The asphaltene fraction is the heaviest part of a crude oil and is obtained as the fraction which contains compounds that are not soluble in paraffinic solvents such as n-heptane. Due to the limited solubility the use of separation methods is strongly reduced to methods that include solvents that dissolve asphaltenes. Here, the direct coupling of size exclusion chromatography with ultrahigh resolution mass spectrometry to investigate the separation of asphaltenes is accomplished. Different mobile phase systems have been investigated using THF and different mixtures of chloroform and toluene to optimize the separation conditions. Due to the separation the complexity of the asphaltene sample can be reduced, therefore mass spectra with increased information depth can be obtained due to the smaller amount of interacting species. Additionally, correlations can be proposed between molecular mass and structural characteristics of highly condensed aromatic molecules: compounds having both aromatic core and long aliphatic chains with higher masses were detected earlier and the smaller ones containing mostly highly aromatic structures and only a low amount of short alkyl chains (with the same DBE values) have stronger retention. Different experimental conditions such as stationary phase and mobile phase of asphaltene separation with size exclusion chromatography are investigated.