FRACTIONATION OF COAL-TAR PITCH BY PLANAR CHROMATOGRAPHY FOR THE CHARACTERIZATION OF LARGE MOLECULAR-MASS MATERIALS

The fractionation of a coal tar pitch by planar chromatography has bee n undertaken in order to develop methodology For improved isolation an d characterization of large molecular mass fractions in coal-derived m aterials. Separated sample fractions were examined by size exclusion c hromatography, UV-absorbance, and UV-fluorescence spectroscopy. The ob served trends show a direct relationship between lack of mobility on t he chromatographic plate and the content of larger molecular mass mate rials; in UV-fluorescence these materials have been found to fluoresce at higher wavelengths. The data provide evidence suggesting the prese nce of very large molecular mass materials in coal tar pitch, supporti ng earlier work based on matrix-assisted laser desorption mass spectro metry, which indicated the presence of high-mass components in the pit ch sample. The use of 1-methyl-2-pyrrolidinone as mobile phase in size exclusion chromatography has enabled the detection of material hither to not observed in solution work involving solvents as powerful as pyr idine and tetrahydrofuran. The planar chromatographic separation has e nabled the detection, and shown a way for the detailed characterizatio n, of high molar mass materials which have normally been masked in stu dies of the unfractionated sample, primarily because of (i) the low co ncentration of the high molecular mass material (15-20% in this sample ), (ii) the low quantum yields of these materials in UV fluorescence, and (iii) their insolubility in common solvents.