ABSTRACT
The analysis of geochemical liquids such as crude oils, hydrothermal bitumens, extracts of coals, and host rocks containing dispersed organic matter or pyrolysates
of sedimentary organic matter of various origins involves several fields. There are investigations of trends in organic matter evolution in sediments including biological origin of organic matter, its thermal maturity (rank) reflecting the degree of its alteration, routes of bitumen migration, and secondary alterations of organic matter, together with problems of geological prospecting of fossil fuel deposits, assessment of fuel quality, and environmental protection. The composition of such mixtures is very complex, with numerous groups of compounds of different polarity, various functional groups, mass weights, and concentrations. Moreover, many compounds of significance in geochemical analysis — among them biomarkers (called also molecular fossils or biological markers) — occur in very low amounts, being efficiently concealed by signals of compounds present in higher concentrations, for example, n-alkanes. Biomarkers, compounds derived from their biological precursors that are synthesized by living organisms in the biosphere, are widely applied in geochemistry for the assessment of source biological organic matter type, its depositional environment, and thermal maturity of organic matter. Their detection, identification, and quantification are commonly performed by means of gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS). To eliminate or at least to reduce such problems as poor quality of mass spectra caused by low levels of biomarker concentrations and contamination of analytical instruments by nonvolatile and highly polar components of organic matter, it is necessary to obtain concentrates of biomarkers. Moreover, the identification of molecular structures of novel biomarkers preformed with such spectral techniques as nuclear magnetic resonance requires the prior isolation of single compounds from a sample, which usually contains compounds of similar chemical properties. Thus, the cleanup of geochemical samples and fractionation into groups of substances showing similar chemical properties and more narrow bands of molecular masses are the necessary first steps in geochemical investigation before any other spectral, pyrolytic, or chromatographic methods can be applied [1-4].
