No abstract

Three essential oils, tea tree oil from Melaleuca alternifolia and two lavender oils (LaVandula angustifolia and LaVandula intermedia laVandin) produced by steam distillation, have been examined by gas chromatography-mass spectrometry (GC-MS) and by size exclusion chromatography (SEC) using 1-methyl-2pyrrolidinone (NMP) as the eluent. This mode of operation of SEC normally produces bimodal chromatograms for petroleum residues, asphaltenes, and coal-derived liquids. Because these volatile oils consist of relatively small molecules, they were seen as a test of the SEC mechanism in eluting terpene molecules and their oxygenated derivatives as small molecules rather than through the formation of aggregates that may masquerade as large molecules. GC-MS confirmed the small molecular types, and the oils eluted from the SEC column only as small molecules. The inclusion of oxygen favored early elution from SEC but not into the excluded region.

A method has been developed using size exclusion chromatography (SEC) in heptane eluent that can detect aliphatics unambiguously without fractionation to remove aromatics. Spherical molecules such as colloidal silicas elute at the exclusion limit, while alkanes up to C 50 elute through the porosity of the column. Detection of aliphatics was defined by use of an evaporative light scattering (ELS) detector with the simultaneous absence of UV absorbance at 300 nm. Alkanes smaller than C 12 were not detected because the conditions of operation of the ELS caused their evaporation. All aromatics eluted after the permeation limit of about 25 min and were not detected until well after 45 min by their UV absorbance. The SEC method was applied to petroleum vacuum residues and coal liquids, and their fractions were soluble in pentane or heptane. High-temperature (HT) GC-MS confirmed the presence of alkanes in the pentane-and heptane-soluble fractions of petroleum vacuum residues, but did not elute any of the aromatics known to be present from SEC. Alkanes were examined in pentane-soluble fractions of a coal digest and a low-temperature coal tar; alkanes up to C 40 were detected in the low-temperature tar and, although present in the digest, were masked by aromatics. No alkanes were detected by either SEC or HT GC-MS in fractions from a coal tar pitch. Aromatics in coal liquids and one petroleum residue were also examined by SEC using NMP as eluent and by UV fluorescence spectroscopy. The SEC method will find application to pentane-and heptane-soluble fractions of petroleum liquids and coal liquids where the alkanes are concentrated relative to the more abundant aromatics.