Identification of large molecular mass material in high temperature coal tars and pitches by laser desorption mass spectroscopy

Parker, John E.; Johnson, Chris; John, P. S.; Smith, Gerald P.; Herod, Alan A.; Stokes, Brian J.; Kandiyoti, R.

doi:10.1016/0016-2361(93)90414-w

Cited by 60 publications

(44 citation statements)

References 23 publications

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“…[6][7][8][9] In these experiments, the reflectron flight path caused loss of detection at high mass but the instrument could not be operated in linear mode. Experiments were conducted at an ion extraction voltage of 20 kV and with a defocused primary beam to prevent the breaking up of sample molecules due to the power of the laser.…”

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confidence: 98%

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

Domin

Moreea

Lázaro

et al. 1997

Rapid Commun. Mass Spectrom.

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Variations in molecular mass distributions observed by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry as a function of changes in the ion accelerating voltage and composition of the matrix have been investigated, using the pyridine-insoluble fraction of a coal tar pitch. With increasing ion extraction voltages (10, 20 and 30 kV) and in the absence of added matrix, spectra clearly showed increases in intensity, particularly at higher masses. The use of higher ion extraction voltages may be considered as providing a more complete inventory of ionized species, apparently significantly enhancing the kinetic energy imparted to larger molecular weight materials. Magnitudes of molecular masses at maximum ion intensity observed using a set of different matrices may be ordered as follows: m/z 1500 [dimethoxy-4-hydroxycinnamic (sinapinic) acid], m/z 1400 (2,5-dihydroxybenzoic acid), m/z 900 [2-(4-hydroxyphenylazo)-benzoic acid], m/z 900 (α-cyano-3-hydroxycinnamic acid), m/z 300 (9-anthracenecarboxylic acid) and m/z 300 (no matrix and a sample loading comparable with the with-matrix experiments). Maximum ion intensities, in the absence of matrix, were found at values which varied from about 300 m/z up to about m/z 1500 as sample loading varied from very low (i.e. suitable for with-matrix operation) up to a visibly black spot. In the absence of a quantitatively based criterion for distinguishing between signal and instrument noise at high mass, accurate high mass limits were not available. However, in each case, ion signals could clearly be observed at values greater than m/z 100 000. The present MALDI spectra do not necessarily show the highest molecular mass materials present in the sample. In view of the observed changes in the spectra with ion extraction voltage and matrix composition, it seems conceivable that higher voltages and/or specific matrices, other than those used in the study, may lead to the detection of larger molecules. © 1997 by John Wiley & Sons, Ltd. Received 23 December 1996; Revised 3 February 1997; Accepted 25 February 1997 Rapid. Commun. Mass Spectrom. 11, 638-645 (1997 Characterization by laser desorption mass spectrometry has considerably extended the range of molecular masses identified in coal-derived liquids. The work was initially undertaken in an attempt to provide independent confirmation for the identification of molecular masses (MMs) up to 4-6000 Da found by size-exclusion chromatography (SEC).1-5 During this preliminary stage of the study, MMs up to the limit of a LIMA (laser ionization mass analysis) instrument (m/z 12 000) were detected in liquefaction extracts and in a coal tar pitch. [6][7][8][9] In these experiments, the reflectron flight path caused loss of detection at high mass but the instrument could not be operated in linear mode. Experiments were conducted at an ion extraction voltage of 20 kV and with a defocused primary beam to prevent the breaking up of sample molecules due to the power of the laser. However, lacking a spectrum additio...

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confidence: 98%

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

Domin

Moreea

Lázaro

et al. 1997

Rapid Commun. Mass Spectrom.

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“…Number average molecular masses for the 'whole' pitch were expected to be relatively low because the sample contains considerable amounts of low MM material (85% pyridine soluble), including some which can be detected by gas chromatography. 3 The calculated values were in the range from 700 up to 4000 u. These fluctuations within a broad band of values was thought to reflect levels of noise and the quality of spectra rather than the upper limit of the spectrum, since low intensities of high-mass ions have little effect on the number average MM value.…”

Section: Number Average Molecular Weights and Peak Mass (Mp)mentioning

confidence: 99%

“…The systematic use of laser desorption mass spectrometry, however, has considerably extended the range of molecular masses that can be detected in 'heavy' coal derived liquids. [2][3][4][5][6][7][8][9][10][11][12][13] Initially, experiments with a LIMA (laser ionisation mass analysis) instrument gave single-shot spectra, showing MMs up to the detection limit of the instrument 2,3 (m/z 12 000). Subsequent linear mode experiments, using a Kratos Kompact MALDI III instrument of more recent conception, allowed extension of the mass range as well as co-addition of the spectra.…”

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Determining a ‘safe’ high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Lázaro¹,

Herod²,

Domin³

et al. 1999

Rapid Commun. Mass Spectrom.

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Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.

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“…Existence in pyrolysis tars of high molecular mass materials between 1000 and 5000 daltons has also been recently observed by laser desorption mass spectrometry [Parker et al, 1993;Herod et al, 1993aHerod et al, , 1993b. It is fair to say, in summary, that there remains some uncertainty as to the molecular weight distribution of the tars, with different methods of characterization suggesting different ranges.…”

Section: A21 Molecular Weight Characterizationmentioning

confidence: 99%

“…They Some other techniques have also been used to examine the molecular weights of vacuum pyrolysis tars and coal derived materials [Winas et al, 1991;Winas, 1991;Herod et al, 1993aHerod et al, , 1993bParker et al, 1993]. Winans et al [1991] compared fast atom bombardment-mass spectroscopy (FAB-MS), laser desorption mass spectrometry (LDMS) and desorption chemical ionization DCI-MS of a vacuum pyrolysis tar.…”

Section: A21 Molecular Weight Characterizationmentioning

confidence: 99%

Vapor pressures and heats of vaporization of primary coal tars

Suuberg¹

1992

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Executive SummaryThis project had as its main focus the determination of vapor pressures of coal pyrolysis tars. It involved performing measurements of these vapor pressures and from them, developing vapor pressure correlations suitable for use in advanced pyrolysis models (those models which explicitly account for mass transport limitations).This report is divided into five main chapters. Each chapter is a relatively "stand-alone" section. Chapter A reviews the general nature of coal tars and gives a summary of existing vapor pressure correlations for coal tars and model compounds. It is shown that the heterogeneous nature and the complexity of coal tars have made it unrealistic to apply detailed vapor pressure correlations which take into account the variation in the chemical structure of the tars. The significant product of this study is a much improved understanding of the volatility and thermal behavior of coal tars. The volatility was studied by vacuum sublimation and Knudsen effusion experiments. The volatility behavior is considerably more complicated than had been earlier believed.The tars evaporate in a "distillation-like" fashion. More volatile species are lost earlier in the process, leaving behind a progressively less volatile residue. The results suggest that there are three very different classes of compounds, and therefore, at least three different vapor pressure behaviors. The first corresponds to compounds of high molecular weight and significant alkyl character, the second to compounds with significant hydroxyl group content and medium molecular weight, and the third to medium molecular weight aromatic compounds without hydroxyl groups. Hydrogen bonding plays a major role in the determining the tar volatility. vi There has been concern in pyrolysis modeling about how closely Raoult's law is followed in coal tar. It appears from our results that the assumption of ideal mixture behavior could be acceptable for rough models of pyrolysis despite the possibility of strong specific interactions between certain functional groups.The results from the current work show that measuring the vapor pressures of complicated and thermally unstable mixtures is possible at low temperatures. There has also been some concern about condensation-type reactions influencing the results of vapor

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Identification of large molecular mass material in high temperature coal tars and pitches by laser desorption mass spectroscopy

Cited by 60 publications

References 23 publications

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

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

Determining a ‘safe’ high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Vapor pressures and heats of vaporization of primary coal tars

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