Size Exclusion Chromatography of Soots and Coal-Derived Materials with 1-Methyl-2-pyrrolidinone as Eluent:  Observations on High Molecular Mass Material

Abstract

A number of samples which eluted at unexpectedly short retention times during size exclusion chromatography have been characterized. Soot and tar samples likely to show similar behavior have been examined. Distinct peaks from about 6 min were observed, compared to 9−10 min for more usual samples. Molecular masses of the early eluting material appear to be large, although extrapolation of existing calibrations does not seem appropriate. A naphthalene mesophase pitch also gave peaks at short elution times. It appears reasonable to interpret chromatograms of this nonpolar material as a direct indication of the presence of large molecular mass material, and to infer that excluded peaks of SEC chromatograms do not necessarily result from the presence of clusters of polar molecules. GC-MS and probe-MS examination of the samples showed only very limited proportions of the samples to have small molecular masses. MALDI-MS spectra of the samples indicated the presence of signal up to 20 000 u. Taken together, data from SEC and the three MS techniques indicated the presence of very large molecular mass materials in this set of samples. Tar deposits recovered from entrained, combusting coal particles have also been examined, providing direct evidence for the presence of large molecular mass material in combustion environments. The observation contrasts with mathematical models of coal burners, where rates of combustion of volatiles are assumed similar to rates of combustion of methane. The nature of the early-eluting material is not known but repeated microfiltration and TEM indicate that it may correspond to molecular diameters in the region of 20 nm. The soots and other samples appear to be in true solution rather than in colloidal suspension.

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

“…The insolubility of the residue appears to have resulted from the remaining material being of molecular masses that were too large to go into solution. The discontinuity observed in all the SEC profiles shown here and for coal-derived samples, 8,11,14 as well as for petroleum residues 14,16,17 and biomass tars, 15 cannot be explained easily, but since the MALDI mass spectra of pitch fractions 10,11 show no discontinuity of mass from around 1000 u up to 100 000 u, it seems probable that the discontinuity may result from a change of molecular shape which becomes possible above a mass of about 3000 u.…”

Matching average masses of pitch fractions of narrow polydispersity, derived from matrix‐assisted laser desorption ionisation time‐of‐flight mass spectrometry, with the polystyrene calibration of SEC

“…The void volume, the earliest elution time of the polymers, was the same for masses above 1.85 million units. A different void volume was found for soots, between 6 and 7 min [9,19]. The calibration indicates that for a series of oligomer molecules, with repeated addition of a structural feature, the decrease of elution time with increasing mass would show regularity.…”

“…We note that the mass spectra do not show a valley of zero intensity starting at m/z 3 -4,000, but show a continuum of mass up to high masses [6] towards m/z 100,000 from samples of wide polydispersity. Also, samples of wide polydispersity [9], including wood soot and an immobile fraction of the pitch derived from planar chromatography, gave MALDI mass spectra with peak masses (m/z) between 3,000 and 6,000. The heptane insoluble fractions of petroleum vacuum residues [18] showed mass ranges in MALDI with a peak of intensity below m/z 1000 but extending to m/z 10,000, which may include some of the material in the SEC exclusion region.…”

Structure and composition of coal tars: An attempt to correlate molecular structure with increasing molecular mass

“…Size Exclusion Chromatography Herod, Lazaro, Suelves et al, 2000) Briefly, a Polymer Laboratories Mixed-D column was operated at 80 C, fed by a Perkin-Elmer LC 250 isocratic pump, and connected to two UVabsorbance detectors: a Perkin-Elmer LC 290 variable wavelength detector set at 450 nm and an Applied Biosystems diode array detector set at 280, 300, 250, and 370 nm. NMP was used as eluent.…”