Isolation of size exclusion chromatography elution-fractions of coal and petroleum-derived samples and analysis by laser desorption mass spectrometry

High-mass species in a coal- and a petroleum-derived sample were investigated by LD-MS of eluent fractions collected from SEC. Results were compared with polymer-based calibrations of SEC elution times. It was observed that polymer- and PAH-based calibrations provide good mass estimates for material eluting in the resolved (later eluting) part of SEC chromatograms. At elution times shorter that 15 min (i.e., in the "excluded" region) there was significant deviation from the PS calibration for both the coal tar pitch and the petroleum-derived samples. In all cases, however, material eluting early during SEC was observed by LD-MS to have higher average masses compared to later-eluting material. The data appears conclusive. An upper limit to the detection of high-mass material by LD-MS appears to have been reached. When comparing mass estimates by LD-MS of SEC elution-fractions of material from the coal tar pitch and petroleum asphaltene, similar molecular mass ranges were found for fractions collected at similar elution times. This provides significant confirmation for the suitability of SEC as a technique for estimating molecular masses of complex hydrocarbon mixtures. The analytical approach presented in this paper provides a valid and useful basis for exploring relationships between molecular size, molecular mass, and structure for complex coal and petroleum-derived materials.