Calibration of Size Exclusion Chromatography in 1-Methyl-2-pyrrolidinone for Coal-Derived Materials Using Standards and Mass Spectrometry M. J. Lazaro, C. A. Islas, A. A. Herod,* and R. Kandiyoti Department of Chemical Engineering and Chemical Technology, Imperial College (University of London), Prince Consort Road, London SW7 2BY, U.K. Received May 24, 1999 This paper describes the elution behavior of model compounds in a polystyrene-divinylbenzene SEC column with NMP as mobile phase, operating at high temperature (80 °C). Model compounds covering polycyclic aromatic hydrocarbons, azaarenes, and other nitrogen and polar compounds have been studied. Most of the standard compounds eluted within one minute of the expected time indicated by the polystyrene calibration. The fractionation of a complex coal-derived sample (a coal tar pitch) using the same column has been achieved, with subsequent reinjection and analysis of the fractions by heated-probe mass spectrometry and UV-fluorescence. The probe- MS experiments were performed in order to show that the material of the excluded peak does not consist of small and polar molecular species, rather than larger-molecular mass material. All the fractions were reinjected and some of them gave small extra peaks in the SEC chromatogram. The earliest fractions showed very weak UV-fluorescence indicating the presence of very high molecular mass material. The later-eluting fractions showed relatively strong fluorescence intensities with the position of the fluorescence intensities shifting to shorter wavelengths as the SEC elution time increased, indicating that the smaller polynuclear aromatic ring systems elute in the late fractions. Probe mass spectra showed that only those fractions isolated from SEC at the long elution times gave signals characteristic of aromatic and nitrogen compounds; the molecular mass range decreased with increasing elution time. Since the structures of the material excluded from the column or even that near the exclusion limit are not known, it is impossible to select standard materials or standard polymeric compounds to represent the molecular mass range of coal-derived liquids. For this reason, we believe that the polystyrene calibration represents the most reasonable compromise for SEC in NMP solvent in our system. Introduction Gas chromatography (GC) and GC coupled to mass spectrometry provide powerful tools for the identifica- tion and structural characterization of unknown com- pounds and mixtures. The identification of azaarenes and thiaarenes in coal-derived liquids by these methods has been reviewed; 1 Nishioaka 2 solvent-extracted coals and compared the pyrolysis product of the extracts with the pyrolysis products from the coal, using GC-MS. Liu and Meuzelaar 3 have examined the products of hydro- pyrolysis of Blind Canyon coal by high-pressure ther- mogravimetry using GC-MS. However, GC and GC-MS normally show up aromatic compounds up to ∼300 u and aliphatic compounds up to ∼500 u. Alternative methods are required for examining samples suspected of containing material with molecular mass (MM) ranges exceeding these limits. The need for more complete information on MM- distributions of coal-derived liquids extends to areas as varied as combustion rates in the near burner zones of power station burners, to the refining and upgrading coal liquefaction extracts and to environmental pollution diagnostics. In attempting to examine the full MM-distribution of complex coal-derived mixtures, size exclusion chroma- tography (SEC) has emerged as one of the more com- monly used techniques [e.g., refs 4-10]. Much of the early SEC work was carried out using tetrahydrofuran (THF) as eluent. 11,12 In our work on coal pyrolysis tars, * Corresponding author. (1) Herod, A. A. Azaarenes and thiaarenes. Handbook of Environ- mental Pollution; Neilson, A. H., Ed.; Springer-Verlag: Heidelberg, Germany, 1997; Chapter 7, p 271. (2) Nishioka, M. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1989, 34 (3), 685. (3) Liu, K.; Meuzelaar, H. L. C. Fuel Proc. Technol. 1996, 49, 1. (4) Handbook of Size Exclusion Chromatography, Chromatographic Science Series, Vol. 69; Wu, Chi-san, Ed.; Marcel Dekker: New York, 1995. (5) Lafleur, A. L.; Nakagawa, Y. Fuel 1989, 68, 741. (6) Herod, A. A.; Shearman, J.; Lazaro, M.-J.; Johnson, B. R.; Bartle, K. D.; Kandiyoti, R. Energy Fuels 1998, 12, 174. (7) Herod,A. 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