FRACTIONATION BY PLANAR CHROMATOGRAPHY OF A COAL-TAR PITCH FOR CHARACTERIZATION BY SIZE-EXCLUSION CHROMATOGRAPHY, UV FLUORESCENCE AND DIRECT-PROBE MASS-SPECTROMETRY

A coal tar pitch, extensively studied by other techniques, has been fr actionated by planar chromatography using successive development in te trahydrofuran, chloroform-methanol (4:1, v/v), toluene and pentane. Pi tch fractions were distinguished by relative retention. The fractions were characterised in solution by size-exclusion chromatography, UV-fl uorescence emission spectroscopy and as the solid on silica, by direct solid-probe mass spectrometry. The method has led to structural infor mation not readily available by direct characterisation of the origina l mixture itself: (i) A progressive shift of UV-fluorescence spectral maximum intensity and molecular mass with decreasing mobility of the f ractions on the planar chromatographic plate, suggesting progressively larger polynuclear aromatic systems; (ii) Nitrogen containing species in the pitch separated from the polynuclear aromatic hydrocarbons whi ch form the bulk of the sample. Neutral and basic nitrogen fractions w ere defined relative to standards and molecular mass numbers in probe mass spectrometry; (iii) Mass ranges of nitrogen components in these f ractions exceed those found previously by GC-MS of the total pitch or its fractions. (iv) Size-exclusion chromatography of the fractions sug gests that polar materials are not simply separated by size.