In-source Pyrolysis Mass Spectrometry Research Articles

Characterization of Large Nonvolatile Polyaromatic Molecules by a Combination of In-Source Pyrolysis and Field Desorption Mass Spectrometry

Nonvolatile hydrocarbon systems, such as those formed via molecular weight growth reactions in refinery processes, normally have a low H/C atomic ratios (<0.5) and high boiling/decomposition points (>600 °C). These materials pose a great challenge to mass spectrometric analysis due to difficulties in vaporization and ionization. In this work, the combination of In-Source Pyrolysis Mass Spectrometry (ISPyMS) and Field Desorption Mass Spectrometry (FDMS) were utilized to obtain compositional information for a nonvolatile organic deposit (foulant) generated by a hydrocracking process. A mixture of polystyrene standards was also analyzed for reference purposes. FDMS yields intact molecular ions for the large polyaromatic systems (∼15 aromatic rings on average). ISPyMS, on the other hand, converts the large multi-core aromatic systems into relatively small single aromatic cores that could be analyzed in detail. In this case, 28 aromatic cores containing short alkyl chains were identified by ISPyMS. Average foulant composition was projected on the basis of IsPyMS and FDMS data. The projected H/C atomic ratio and aliphatic carbon/aromatic ratio match well with those measured by elemental analysis and solid-state 13C NMR.

Essential role of caffeoyl coenzyme A O-methyltransferase in lignin biosynthesis in woody poplar plants.

Caffeoyl coenzyme A O-methyltransferase (CCoAOMT) has recently been shown to participate in lignin biosynthesis in herbacious tobacco plants. Here, we demonstrate that CCoAOMT is essential in lignin biosynthesis in woody poplar (Populus tremula x Populus alba) plants. In poplar stems, CCoAOMT was found to be expressed in all lignifying cells including vessel elements and fibers as well as in xylem ray parenchyma cells. Repression of CCoAOMT expression by the antisense approach in transgenic poplar plants caused a significant decrease in total lignin content as detected by both Klason lignin assay and Fourier-transform infrared spectroscopy. The reduction in lignin content was the result of a decrease in both guaiacyl and syringyl lignins as determined by in-source pyrolysis mass spectrometry. Fourier-transform infrared spectroscopy indicated that the reduction in lignin content resulted in a less condensed and less cross-linked lignin structure in wood. Repression of CCoAOMT expression also led to coloration of wood and an elevation of wall-bound p-hydroxybenzoic acid. Taken together, these results indicate that CCoAOMT plays a dominant role in the methylation of the 3-hydroxyl group of caffeoyl CoA, and the CCoAOMT-mediated methylation reaction is essential to channel substrates for 5-methoxylation of hydroxycinnamates. They also suggest that antisense repression of CCoAOMT is an efficient means for genetic engineering of trees with low lignin content.

Direct temperature-resolved mass spectrometry as a technique for the semi-quantitative analysis of marine particulate organic matter

To date, direct temperature-resolved mass spectrometry (DT-MS, a form of temperature-resolved, in-source pyrolysis mass spectrometry) has generally been used to provide qualitative views of the broad-band molecular-level characteristics of complex organic samples. In this paper low voltage electron impact (EI +) DT-MS is used to provide semi-quantitative information on molecular-level characteristics of marine particulate organic matter (POM) samples. This class of samples is analytically challenging for two main reasons. Firstly, it is difficult to obtain representative data sets in which sample sizes are sufficient for characterization. Secondly, marine organic matter samples contain many identifiable compound classes in conjunction with a substantial percentage of as-of-yet uncharacterizable material. As a first step toward quantitation, DT-MS analysis of selected standards was used to determine relative response factors of common compound classes identified in marine organic matter. These response factors were then used to quantify the relative contribution of the compound classes in two natural POM samples. The potential of DT-MS as a quantitative technique was then further explored by comparing DT-MS determinations of particulate organic carbon to chlorophyll ratios (POC/chl) in natural POM samples with the same ratios determined by elemental analysis and liquid chromatography (HPLC), a technique currently employed by marine chemists.

Macromolecular composition of the propagule wall of Nelumbo nucifera

The macromolecular constituents of the sclerotic propagule wall of Nelumbo nucifera and seed coat of Nymphaea caerulea were studied using scanning electron- and light microscopy in combination with Curiepoint pyrolysis-gas chromatography-mass spectrometry. In addition, the Nelumbo material was analyzed using solid state 13C nuclear magnetic resonance and in-source pyrolysis-mass spectrometry. The sclerotic seed coat of the Nymphaea caerulea revealed the presence of angiosperm lignin-cellulose similar to that found in most sclerotic plant remains. In sharp contrast, the fruit wall plus seed coat of Nelumbo is believed to be composed of a complex of polysaccharides, based on primarily galactose and mannose units, and insoluble tannins, which are suggested to play the same structural role as the lignin-cellulose in the sclerotic seed coat. The distinctive nature of the chemical constituents present in the propagule wall of Nelumbo, supports the systematic distinction of this genus in the separate family Nelumbonaceae. The characteristic chemical composition of the propagule walls of Nelumbo could be an additional factor in favour of a prolonged longevity of these fruits. However, the distinctive composition of polysaccharides and tannins without the presence of lignin is considered to be the main reason for the absence of these propagules in the fossil record, despite their physical resistance.

Analytical pyrolysis experiments of Titan aerosol analogues in preparation for the Cassini Huygens mission

Comparative pyrolysis mass spectrometric data of Titan aerosol analogues, called “tholins”, are presented. The Titan tholins were produced in the laboratory at Cornell by irradiation of simulated Titan atmospheres with high energy electrons in plasma discharge. Mass-spectrometry measurements were performed at FOM of the solid phase of various tholins by Curie-point pyrolysis Gas-Chromatography/Mass-Spectrometry (GCMS) and by temperature resolved insource Pyrolysis Mass-Spectrometry to reveal the composition and evolution temperature of the dissociation products. The results presented here are used to further define the ACP (Aerosol Collector Pyrolyser)-GCMS experiment and provide a basis for modelling of aerosol composition on Titan and for the interpretation of Titan atmosphere data from the Huygens probe in the future.

A combined pyrolysis mass spectrometric and light microscopic study of peatified Calluna wood isolated from raised bog peat deposits

Stem wood of the Angiosperm Calluna vulgaris (Scotch heather), isolated at different depths from a selection of raised bog peat deposits, was chemically characterized using in-source pyrolysis mass spectrometry (Py-MS) and Curie-point pyrolysis gas chromatography mass spectrometry (Py-GC-MS). Light microscopy was performed to relate mass spectrometric characteristics with anatomical features. Peatified wood samples, isolated from increasing depth show a gradual decrease in carbohydrate content. This decrease in anatomically reflected in a selective removal of secondary cell wall material from the fibre-tracheids and wood parenchyma. During prolonged peatification a selective removal of hemicellulose sugars is observed, while a part of the cellulose fraction is preserved. This highly resistant cellulose is mainly located in the secondary cell walls of the vessels. The lignin macromolecule is preserved, but a gradual decrease in syringyl to guaiacyl ratio (S/G) is observed during peatification. Because no increase in catechol and phenolic compounds is observed, we conclude that S/G shifts are due to removal the of syringyl-rich secondary cell wall material and the retention of guaiacyl-rich compound middle lamella. Small chemical changes in the lignin macromolecule involve shifts in oxygen substitutions on the aliphatic side chains of the methoxyphenolics and the occurrence of aromatic acids.

Structural characterization of lignin polymers by temperature-resolved in-source pyrolysis—mass spectrometry and Curie-point pyrolysis—gas chromatography/mass spectrometry

Temperature-resolved in-source pyrolysis—mass spectrometry (Py—MS) and complementary Curie-point pyrolysis—gas chromatography/mass spectrometry (Py—GCIMS) were used to characterize a set of lignin polymers. No sample pretreatment was required and over 100 thermal degradation products were identified in the pyrolysates. Results were compared with whole biomass reference materials. Coniferyl alcohol and sinapyl alcohol, which were formed upon pyrolysis of lignin, could be selectively ionized by ammonia chemical ionization (Cl). Curie-point Py—GC with flame ionization detection was applied to classify the lignin polymers according to syringyl/guaiacyl ratios, the number of preserved phenylpropane structural units and functional group content. Multivariate analysis of the in-source Py—MS data was employed to classify the lignin polymers according to the origin and degree of modification. Combined results showed that enzyme-treated cottonwood-milled wood lignin is a relatively homogeneous polymer with a large fraction of preserved alkyl-aryl ether linkages. Technical lignins, isolated by the steam-explosion, organosolv and Kraft pulping processes, were found to be modified depending on the severity of the isolation procedure employed, and contained large amounts of β — 1-linked stilbene and β — β-linked resinol types of structures. Bagasse lignin shows the most condensed polymer structure with a large proportion of ether bonded p-coumaric acid and ferulic acid.

Structural biopolymer preservation in Miocene leaf fossils from the Clarkia site, northern Idaho.

The 17- to 20-million-year-old locality at Clarkia, northern Idaho, is renowned for yielding amplifiable DNA from a magnolia leaf fossil. In-source pyrolysis-mass spectrometry and pyrolysis-gas chromatography/mass spectrometry now reveal that molecular preservation of biomacromolecules is highly selective; structural polysaccharides, cutin polyesters, and proteins were not preserved in detectable quantity in the leaf tissues, whereas both lignin and an aliphatic biopolymer were detected. This study points up the need for improved understanding of the precise modes and extent of preservation of biomacromolecules in fossil materials and sediments.

Analytical pyrolysis mass spectrometry: new vistas opened by temperature-resolved in-source PYMS

Analytical pyrolysis mass spectrometry (PYMS) is introduced and its applications to the analysis of synthetic polymers, biopolymers, biomacromolecular systems and geomacromolecules are critically reviewed. Analytical pyrolysis inside the ionisation chamber of a mass spectrometer, i.e. in-source PYMS, gives a complete inventory of the pyrolysis products evolved from a solid sample. The temperature-resolved nature of the experiment gives a good insight into the temperature dependence of the volatilisation and pyrolytic dissociation processes. Chemical ionisation techniques appear to be especially suitable for the analysis of oligomeric fragments released in early stages of the pyrolysis of polymer systems. Large oligomeric fragments were observed for linear polymers such as cellulose (pentadecamer), polyhydroxyoctanoic acid (tridecamer) and polyhydroxybutyric acid (heneicosamer). New in-source PYMS data are presented on artists' paints, the plant polysaccharides cellulose and xyloglucan, several microbial polyhydroxyalkanoates, wood and enzyme-digested wood, biodegraded roots and a fossil cuticle of Miocene age. On-line and off-line pyrolysis chromatography mass spectrometric approaches are also discussed. New data presented on high temperature gas chromatography—mass spectrometry of deuterio-reduced permethylated pyrolysates of cellulose lead to a better understanding of polysaccharide dissociation mechanisms. Pyrolysis as an on-line sample pretreatment method for organic macromolecules in combination with MS techniques is a very challenging field of mass spectrometry. Pyrolytic dissociation and desorption is not at all a chaotic process but proceeds according to very specific mechanisms.

Characterisation of polysaccharides by in-source pyrolysis positive- and negative-ion direct chemical ionisation-mass spectrometry

Series of oligosaccharide ions have been generated from a range of polysaccharides by the application of in-source pyrolysis mass spectrometry, using both ammonia positive-ion chemical ionisation and negative-ion chlorine-nucleophilic-addition ionisatioin. Glucans with α-(1 → 6),β-(1 → 6),α-(1 → 4), β-(1 → 4), β-(1 → 3), and β-(1 → 2) linkages were studied, together with pentosans, xyloglucans, and an arabinogalactan. The series of ions correspond to intact, desorbed oligosaccharides with a terminal anhydro-sugar unit, and to similar oligosaccharides with attached sugar ring-cleavage fragments. The ions generated are dependent on the position of the linkage and ring size, and retain significant information on the structure of the original polysaccharide.