Improving compositional space accessibility in (+) APPI FT-ICR mass spectrometric analysis of crude oils by extrography and column chromatography fractionation

Abstract

Separation strategies coupled with HRMS analysis are vital to increase the scope of the instrumental technique. In this work, we use extrography and column chromatography as fractionation tools for increasing compositional space accessibility in the APPI-FT-ICR mass spectrometric analysis of heavy crude oils. Extrography fractionation was performed on a crude oil sample adsorbed on neutral alumina, using an elutropic series. The crude oil was adsorbed on neutral alumina, and then we applied Soxhlet extraction using acetonitrile, methanol, n-heptane, and toluene, to obtain fractions enriched in metal complexes, polar compounds, maltenes, and asphaltenes, respectively. Considering that polar compounds are responsible for complex operational problems such emulsion and deposit formation, we fractioned the polar extract using normal phase column chromatography to obtain six additional subfractions. All of the extracts were analyzed by APPI FT-ICR mass spectrometry. We detected eleven compound classes in fractions and sub-fractions which were undetectable when analyzing the entire crude oil sample. In terms of the number of molecular formulas, the whole crude oil sample exhibits ∼3700 while ∼11,800 compounds were detected in extrography fractions and column chromatographic sub-fractions. These results indicate that combination of extrography and column chromatography increase compositional space accessibility in around 70%. Specifically, fractionation processes allowed the detection of several compound classes such as NnSs, NnOo, OoSs, NnOoSs (with n=1; s=1, 2, 3; o=1, 2, 3), and N4O1V1, which were undetectable in the analysis of the whole crude oil.