Multimode size exclusion chromatography with poly(divinylbenzene)/N-methylpyrrolidinone for the characterization of coal-derived mixtures

This paper describes experiments carried out within the framework of examining capabilities of MALDI-TOF-MS in the characterisation of fossil fuels and related materials. The work has focused on the effect of interactions between sample structure and matrix composition on the quality of MALDI spectra. Solvent extracts from six kerogens have been examined by MALDI-MS in the presence of three matrices of different composition and in the absence of matrix (laser ablation). The kerogen extracts have also been characterised by size exclusion chromatography (SEC) and UV-fluorescence spectroscopy (UV-F). In the presence of the three matrices (sinapinic acid, 2,5-dihydroxybenzoic acid and α-cyano-3-hydroxycinnamic acid), spectra of extracts from the three geologically 'younger' kerogens showed larger molecular mass distributions compared to spectra of extracts from the corresponding 'older' kerogens. This result directly contradicted trends observed in the absence of matrix, where extracts from 'older' kerogens showed larger molecular mass distributions. Results from SEC and UV-F agreed with trends observed in MALDI-spectra acquired in the presence of matrix, particularly sinapinic acid. By contrast, we recently reported that high mass signal in laser ablation mass spectra of the pyridine-insoluble fraction of a coal tar pitch, obtained in the absence of matrix, closely matched signals obtained in the presence of sinapinic acid. Compared to the highly condensed aromatic structure of the coal tar pitch, the kerogen extracts (of considerably higher oxygen content) appear less able to readily absorb incident laser radiation (337 nm) in the absence of externally added matrix. The argument is consistent with apparently more efficient absorption of incident laser radiation by the geologically 'older' samples, when no matrix was used. Structural characteristics suggest that the geologically 'older' samples would be better able to act as 'self-matrix'. Thus, differences in structure and composition of the samples appear to go some way towards explaining differences between trends observed in the presence/absence of matrix. Dependence of MALDI spectra on molecular structure has also been found for two sets of biomass derived samples. Considerably more work appears warranted to determine MALDI-MS parameters appropriate to the analysis of the more oxygenated, lower rank, samples. Recently, 1,2 we described changes in the MALDI-TOF mass spectra of coal derived liquids as a function of changes in (i) ion extraction voltage, (ii) laser power (iii) matrix composition and (iv) sample deposition density. Increasing ion extraction voltages helps provide a more complete inventory of species already ionised, without otherwise disturbing the sample. It would appear advantageous, therefore, to use the highest possible values of the extraction voltage, apparently irrespective of other experimental parameters. Clearly, the upper limit of the ion extraction voltage is determined by the capabilities of installed hardware. We have, to date, been a...

Section: Polarity Vs Molecular Mass In Secmentioning

confidence: 98%

Section: Polarity Vs Molecular Mass In Secmentioning

confidence: 99%

Section: Polarity Vs Molecular Mass In Secmentioning

confidence: 99%

See 1 more Smart Citation

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of kerogen extracts: effect of interactions between sample structure and matrix

Herod

Lázaro

Rahman

et al. 1997

“…The elution volume corresponding to the largest polystyrene used here was found to be approximately 4.5 mL, equivalent to an elution time of 9 min at 0.5 mL/min -1 and a polystyrene molar mass of about 2 000 000 Da. The calibration curves have been presented elsewhere; 19 similar calibration curves using NMP have been shown 12 with two linear regions, above and below the exclusion limit. The effective limit of the column defined by the void volume is not known.…”

Section: Size-exclusion Chromatographymentioning

confidence: 99%

“…Earlier work by Lafleur and Nakagawa 12 had already demonstrated the successful use of 1-methyl-2-pyrrolidinone (NMP), a more polar solvent than THF, as an eluent in SEC. In attempting to characterize material eluting at the exclusion limit of the column (i.e.…”

mentioning

confidence: 99%

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

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...

Pyrolysis-gas chromatography/mass spectrometry of a coal extract and its fractions separated by planar chromatography: correlation of structural features with molecular mass

Islas

Suelves

Carter

et al. 2000

The structural characterisation of a coal liquefaction extract and its three fractions separated by planar chromatography has been described. Size exclusion chromatography showed the molecular mass distributions to become progressively larger with decreasing mobility on the plate. UV‐fluorescence spectroscopy of the fractions indicated parallel increases in the sizes of polynuclear aromatic ring systems. Analysis by probe‐mass spectrometry of the ‘whole’ coal extract showed the expected array of small polynuclear aromatic groups extending to m/z 450. The probe mass spectra of the lightest fraction (‘mobile in pyridine and acetonitrile’) showed similar features, except for effects due to vacuum drying to remove solvent. In sharp contrast, the two heaviest fractions (‘mobile in pyridine and immobile in acetonitrile’ and ‘immobile in pyridine’) showed no significant ions other than those from residual NMP solvent (m/z 98 and 99). Pyrolysis‐gas chromatography/mass spectrometry of these two heaviest fractions showed only traces of aromatic compounds or fragments. The aromatic pyrolysis products of these fractions were too large and involatile to pass through the GC column. The major components observed in the pyrolysis‐gas chromatography/mass spectrometry of the two heavy fractions were alkanes and alkenes, ranging between C10–C25. Since none of the samples contained free alkanes, alkenes or cycloalkanes before pyrolysis, they were generated during the pyrolysis step. The shifts of UV‐fluorescence spectral intensity to shorter wavelengths with decreasing size indicated by size exclusion chromatography (SEC) provide direct evidence of differences in structure with changing molecular mass. This evidence strongly suggests that species identified as being of large molecular mass in this extract sample are not composed of molecular aggregates. It remains difficult to establish whether and when it would be legitimate to invoke molecular aggregates to explain the large molecular masses (MMs) identified here and in other work. Copyright © 2000 John Wiley & Sons, Ltd.