Applications of inverse chromatography in organic geochemistry—II. Measurement of solute activity coefficients in organic geopolymers by gas chromatography

Gas chromatography has been used to measure the molal activity coefficiets of a series of nonpolar organic solutes in sedimentary organic matter and its various extractable components. Organic matter from a peat deposit of higher plant origin in the Florida Everglades was isolated at three depths in the peat core. The organic matter was then fractionated into its lipid, humic acid and humin components, and the activity coefficients measured for solutes ranging in electronic polarizability from pentane to dichloroethane. Activity coefficients, which are a thermodynamic measure of the affinity of a solute for a polymeric solution, show a reasonable correlation with electronic polarizability for the total organic matter and its lipid and humin fractions. There is also a marked increase in he lipophilic character of the humin fraction with increasing depth of burial. In spite of this chage in humin solution capabilities, however, all of the solutes exhibit decreased affinities for the deeper total organic matter, which we believe is due to its lower lipid content, as well as a somewhat lower affinity for the more mature lipid fraction. Solid state 13C NMR spectra of the unfractioned organic matter and the humic acid and humin fractions give some insight into the relatoinship between their structure and sorption characteristics, although the chemical basis for the evolution of the nonpolar, lipophilic humin at depth is not readily apparent.