Characterization of coal by matrix‐assisted laser desorption ionization mass spectrometry. I. The argonne coal samples

Abstract

The Argonne set of coals cover the rank range from lignite to semi-anthracite; these samples have been studied by matrix-assisted laser desorption mass spectrometry (MALDI-MS) in a time-of-flight mass spectrometer equipped with a nitrogen laser at 337 nm, using sinapinic acid as matrix. The coal particle size was less than 5 microns. The characteristics of the MALDI-MS spectra of the set of coals were found to be rank-related; desorption from highrank coals was found to take place with greater relative ease than from low-rank coals. Two major features were found in all spectra: a homologous series of peaks in the 200-500 u mass range and an intense peak between lo00 and SOOOu, the particular shape of the peak depending on coal rank. A continuum of lower intensity peaks extending to very large molecular masses was found in all spectra, the upper limit of molecular masses increasing with coal rank at the same laser fluence. The effect of changes in laser power on spectra was investigated: upper mass limits were found to increase with power up to the detection limit of the instrument but low-mass parts of spectra were found to distort, possibly due to detector overloading. A maximum laser fluence value acceptable over the coal-rank range represented by these samples could therefore not be easily defined. None of the mass spectra showed evidence of the presence of either carbon clusters or fullerene formation, indicating that laser fluences did not reach intensities high enough to induce substantial secondary reactions. Comparing molecular mass distributions detected by MALDI of coal pyrolysis tars and directly from coals suggests the MALDI and pyrolytic mechanisms of volatile release to be structurally different; in particular, the preferential evaporation of lighter species which occurs during pyrolytic tar evolution (and during field-ionization mass spectroscopy) appears to evolve material with a more restricted range of molecular masses compared to laser desorption mechanisms.

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

“…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]. At the meantime, the type of mass analyzer most widely used with LD and MALDI is time-of-flight (TOF), which can well separate ions with relative high mass-to-charge ratio (m/z).…”

“…Herod and co-workers have developed MS methods such as laser desorption (LD)-MS and matrix-assisted laser desorption/ionization (MALDI)-MS for the characterization of heavy hydrocarbons from coal, petroleum and kerogen [12][13][14][15][16]. 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].…”

Choice of Extraction Voltage and Matrix in the Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry of Coal Tar Pitch — Pyridine Insolubles

“…Extension of the work using more up-to-date matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) instruments enabled the range of MMs to be extended, with the identification of ions between m/z 20 000 and 30 000 in pyrolysis tars and liquefaction extracts 10 and up to m/z 270 000 in solid coals. 11 This instrument allowed the addition of spectra and was used in the linear mode. These findings, once again, reflected the detection limit of the instrument (Kratos Kompact MALDI III), and went far beyond the MM-range previously identified by SEC, where tetrahydrofuran (THF) had been used as eluent.…”

Comprehensive Two-Dimensional Gas Chromatography and Its Application to the Investigation of Pyrolytic Liquids

“…Extracts of liquefaction and coal tar were analyzed by laser desorption (LD)-MS and matrixassisted laser desorption/ionization (MALDI)-MS for the determination of the molecular mass (MM) distribution, and results were compared to size exclusion chromatography (SEC) [77].…”