Pyrolysis-gas chromatography/mass spectrometry of fractions separated from a low-temperature coal tar: an attempt to develop a general method for characterising structures and compositions of heavy hydrocarbon liquids.

A low-temperature coal tar has been fractionated by column chromatography into acetonitrile, pyridine and 1-methyl-2-pyrrolidinone- (NMP) solubles. The tar and its fractions have been examined by pyrolysis-gas chromatography/mass spectrometry (GC/MS). Fractionation by planar chromatography was also carried out for purposes of comparison. Molecular masses of the fractions were estimated by size-exclusion chromatography (SEC), and bulk structural characterisation was carried out by (13)C-NMR and UV-fluorescence spectrometry. SEC showed that the fractions shifted to progressively shorter elution times (higher apparent masses) with diminishing solubility, i.e. from acetonitrile to NMP solubles. UV-fluorescence spectra showed parallel shifts to longer wavelengths and lower fluorescence quantum yields, indicating increasing sizes of aromatic ring systems and increasingly complex molecules. GC/MS analysis of the tar showed alkanes from C10 to C32 and extensive series of alkylated aromatics, phenols, indenes, naphthalenes, phenanthrenes and fluoranthenes. Pyrolysis-GC/MS results for the acetonitrile solubles closely resembled the data for the tar sample, with extensive series of alkylated benzenes, phenols and naphthalenes as well as alkanes from C16 to C28. The pyridine-soluble fraction showed no significant aromatic pyrolysis products and only relatively weak signals for alkanes between C16 and C27. The NMP-soluble fraction showed even less overall signal, with no significant aromatic components and weak signals for alkanes between C21 and C25, even though (13)C-NMR analyses showed that approximately half of the carbon detected was aromatic. The aliphatics are assumed to provide bridging structures between polycyclic aromatic (PCA) ring systems.

Structural characterisation of Baltic amber and its solvent extracts by several mass spectrometric methods.

A sample of Baltic amber ( approximately 40 million yrs old) has been extracted using pentane, toluene and 1-methyl-2-pyrrolidinone (NMP). The relationship between solubility characteristics of the extracts in relation to molecular mass and chemical makeup has been investigated. The extracts were first characterised by (13)C-NMR spectrometry, size exclusion chromatography (SEC) and UV-fluorescence spectroscopy. The fractions differed less in terms of chemical structural features than they did in terms of molecular mass. This contrasts markedly with data on fractions of coal-derived liquids, but parallels results from petroleum-derived vacuum residues. In SEC, the toluene soluble/pentane insoluble fraction gave a peak for high mass material at about 67 000 u. Material excluded from the column porosity in this fraction and in NMP solubles eluted between 8 and 11 min, corresponding to polystyrene masses between 200 000 and several million u. A column with a larger pore size distribution was calibrated using polystyrene and polymethylmethacrylate standards with detection by a light-scattering evaporative analyser. The largest polystyrene standard (15.4 million u) eluted at 13.4 min, similar to that of the earliest eluting amber-derived material in the NMP solubles fraction. Results from probe-MS and pyrolysis-GC/MS have been used to confirm the similarity of chemical structures of the three solubility fractions. Broadly, low mass ions appear to correspond to the various monomeric units of structures present in the amber, the higher mass ions to dimer units and the molecular ions to the different combinations of three or more monomeric units. The main monomer groups have been identified in detail, showing a situation very different from that of coal-derived materials, where the sizes of aromatic ring systems increase with molecular size.