The high‐mass component (>m/z 10 000) of coal tar pitch by matrix‐assisted laser desorption/ionisation mass spectrometry and size‐exclusion chromatography

Abstract

The size-exclusion chromatography (SEC) of acetone-soluble, pyridine-soluble and pyridine-insoluble fractions of a coal tar pitch indicates a bimodal distribution in each fraction. The proportion of high-mass material excluded from the SEC column porosity increases with solvent polarity. The polymer calibration of SEC shows the mass range of the small molecules to be from approximately 100 u to approximately 6000 u, with the mass range of the large excluded molecules above 200 000 u and up to several million u. In contrast, matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) shows a similar low-mass range of ion abundances (< m/z 6000), but with a smaller range of high-mass ion abundances, from approximately m/z 10 000 to 100 000. The large molecules may have three-dimensional structures to allow molecules of relatively low mass to behave as if they are of large size in SEC. Laser desorption mass spectrometry of the acetone- and pyridine-soluble fractions produced molecular ions of polycyclic aromatics that can be related to the known compositions from gas chromatography (GC) mass spectrometry. The experimental conditions used to generate the bimodal distribution by MALDI-MS involve reducing the ion signal intensities to avoid overload of the detector and enable detection of the high-mass ions, by reducing the high-mass detector voltage (i.e. sensitivity) and increasing the laser power.

Molecular characterization of heteroatomic compounds in a high-temperature coal tar using three mass spectrometers

“…Although much more species were detected by ASAP-TOF MS and ESI-Orbitrap MS, only a tiny portion of the species was hydrocarbons. Unlike previous report analyzing coal derived liquids using MALDI-MS [17], carbon number of the compounds detected by GC/MS and ASAP-TOF MS was less than 20 (a relatively low molecular weight compared to molecules identified by MALDI-MS), and the corresponding DBE mainly distributed between 0-10. Furthermore, there was an approximate linear relationship between the DBE value and carbon number, which was also found in middle-temperature coal tar due to the increase of double bond or aromatic ring [43].…”

“…Broader molecular mass distributions were detected from coal-derived liquids compared to other mass spectrometric techniques [17], because laser desorption ionization could ionize molecules with relatively higher molecular mass [18]. Compared to LD-MS, MALDI-MS improves the sensitivity to high-mass material and expands the detection range of molecular mass up to m/z 270,000 for fossil fuels [14,19,20].…”

Preparation of Organic Light-Emitting Diode Using Coal Tar Pitch, a Low-Cost Material, for Printable Devices

“…The PL wavelength was the shortest (429 nm) for solution 1a (cyclohexane) and the longest (550 nm) for solution 1f (CHCl 3 ). Most importantly, the PL wavelength of the coal tar pitch solution could be controlled by appropriate choice of the solvent, similar to a previously reported case in which the PL spectra in two different solvents were compared [17], [28].…”

The Pentane- and Toluene-Soluble Fractions of a Petroleum Residue and three Coal Tars by Size Exclusion Chromatography and UV-Fluorescence Spectroscopy

“…The presence of components excluded from the porosity of the SEC column, eluting between 9-13 min may be interpreted as showing the presence of large molecules, and/or possibly indicating the presence of three-dimensional structures or conformations (eluting earlier than would be warranted by their molecular masses alone) rather than of aggregates of the small polar components [1,24,25] of coal tars, identified by GC-MS analysis. The first pentane fraction chromatograms showed some low intensity excluded material in the coal derived liquids.…”