High Mass Materials Research Articles

Characterization of Molecular Mass Ranges of Two Coal Tar Distillate Fractions (Creosote and Anthracene Oils) and Aromatic Standards by LD-MS, GC-MS, Probe-MS and Size-exclusion Chromatography

Laser-desorption mass spectrometry (LD-MS) method development was undertaken to improve estimates of mass ranges for complex hydrocarbon mixtures. A creosote oil, an anthracene oil, and a mixture of known polynuclear aromatic hydrocarbon (PAH) compounds were examined. The data on the mixture of the four PAHs made it possible to define LD-MS conditions necessary to generate artifacts such as cluster ions by the combination of high laser power and high-mass accelerator voltage. The formation of cluster ions was possible without overloading the detector system. These multimer ions overlapped with higher-mass ion signals from the sample. However, careful balancing of sample concentration, laser power, total ion current, and delayed ion extraction appears to show high-mass materials without generating high-mass multimer (artifact) ions. It is possible to suppress the formation of cluster ions by keeping low target concentrations and, consequently, low gas phase concentrations formed by the laser pulse. The principal method used in this work was the fractionation of samples by planar chromatography followed by successive LD-MS analysis of the separated fractions directly from the chromatographic plates. This method separated the more abundant small molecules from the less abundant large molecules to permit the generation of their mass spectra independently, as well as reducing the concentration of sample by spreading over the PC-plate. The technique demonstrably suppressed multimer formation and greatly improved the reproducibility of the spectra. Results showed the presence of molecule ions in the ranges m/z 1000−2000 for the anthracene oil sample and m/z 600−1500 for the creosote oil sample, tailing off to m/z ∼5,000. The creosote oil contained significantly less of this high-mass material than the anthracene oil sample, and in both cases, high-mass material was only present in low quantities. Ion mass range estimates were in close agreement with molecular mass ranges from size exclusion chromatography, and findings were consistent with changes observed in the UV-fluorescence spectra. The method outlined in the paper appears directly applicable to the characterization of heavier coal and petroleum derived fractions.

Heat Flow through Soils and Effects on Thermal Storage Cycle in High-Mass Structures

The solar radiation absorbed in massive building components is stored and later emitted as long-wave thermal radiation into the interior space. Heat storage capacity is directly related to the mass of the building envelope surrounding this space and particularly that of high-mass, homogeneous earthen or cementitious material. A thermal storage cycle is created by the time-lag effect if sufficient mass is available. A similar strategy applied to the lunar and/or Martian regolith would provide a surface structure with micrometeorite and radiation protection, thermal insulation, and natural supplemental heat energy that would significantly reduce the energy requirements met by mechanical equipment. HEAT2 is an energy simulation program that solves heat transfer problems using the partial differential heat conduction equation in two dimensions with the method of explicit finite differences. HEAT2 simulation data suggests that, although thermal mass is most suitable for climates where desired indoor temperatur...

Characterising high mass materials in heavy oil fractions by size exclusion chromatography and MALDI-mass spectrometry

Several petroleum vacuum residues and a Maya asphaltene have been examined using size exclusion chromatography (SEC), using 1-methyl-2-pyrrolidinone as eluent. Aliphatic components are not dissolved in this solvent. All the samples showed a bimodal distribution. Material under the early eluting peak, excluded from column porosity corresponded to apparently very large molecular masses. The later eluting peak corresponded to molecules with a smaller range of masses and was relatively intense. The material excluded from column porosity is concentrated in the heptane-insoluble fraction; the peak of this fraction corresponding to smaller molecules shifted to earlier times than was found for the whole sample. In UV-fluorescence spectrometry, the heptane-insoluble materials did not fluoresce strongly. Materials excluded from column porosity showed no fluorescence, indicating that UV-fluorescence based methods are unable to detect high mass materials. MALDI-mass spectrometry indicated a bimodal distribution for the Maya asphaltene with a mass range up to m/ z 40,000. Comparison of the low mass range of the spectrum with the small-size molecules detected by SEC indicated broad agreement for masses up to about 5000 u. However, if the excluded peak of SEC corresponds to the higher mass range up to m/ z 40,000, then it is likely that these molecules are adopting three-dimensional conformations. Data from the hydrocracking of heavy oils was used to confirm some of the outlined findings.

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

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.

04/01242 The unusual properties of high mass materials from coal-derived liquids: Islas, C. A. et al. Fuel, 2003, 82, (14), 1813–1823

04/01242 The unusual properties of high mass materials from coal-derived liquids: Islas, C. A. et al. Fuel, 2003, 82, (14), 1813–1823

The Calibration of Size Exclusion Chromatography Columns: Molecular Mass Distributions of Heavy Hydrocarbon Liquids

The aim of the study was to obtain calibration curves for a pair of size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent. The dependence of the calibrations on sample chemical structures has been examined. The calibrations have been compared with elution times of several sets of standards. The level of agreement between SEC and MALDI-mass spectrometry has been evaluated. Molecular mass distributions of several complex samples have been examined in terms of these calibrations. The polystyrene (PS) and poly(methyl methacrylate) (PMMA) calibration curves were close, while a set of polysaccharides (PSAC) and other oxygenates eluted much earlier. However, numerous other samples eluted closer to the PS−PMMA line. To a first approximation, deviations between the PSAC and PS−PMMA lines may be treated as an upper limit to errors arising from structure-dependent variations in this SEC system. Below 15 000 u, MMs of oxygenated samples could be estimated to within a factor of ∼2−2.5. Other structural features gave rise to smaller deviations. Good agreement was observed up to about m/z 3000, between SEC and MALDI and LD-MS. The techniques are independent, suggesting that up to this limit, SEC may be considered as a quantitative tool. The accuracy of the measurement is subject to greater uncertainty with increasing molecular mass. The often-made assumption that high-mass materials are composed of aggregates has been examined. Furthermore, evidence from several analytical techniques provides indications of entirely different structural makeup (e.g., nature of fragments in mass spectrometry; trace element concentration) between fractions with different apparent molecular massesas determined by SEC. It is possible that some molecules adopt 3-dimensional conformations and show up as larger than they really are. While the “aggregates” assumption did not explain our experimental observations, structures of material appearing under the excluded peak in SEC require further careful study.

Planar chromatographic separation for the rapid determination of high mass materials in coal derived liquids : Islas, C. A. et al. Preprints of symposia — American Chemical Society, Division of Fuel Chemistry, 2002, 47, (2), 647–648

Planar chromatographic separation for the rapid determination of high mass materials in coal derived liquids : Islas, C. A. et al. Preprints of symposia — American Chemical Society, Division of Fuel Chemistry, 2002, 47, (2), 647–648

Chromatographic separation of large quantities of high mass materials from coal derived liquids : Islas, C. A. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2002, 47, (2), 643–644

Chromatographic separation of large quantities of high mass materials from coal derived liquids : Islas, C. A. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2002, 47, (2), 643–644

The unusual properties of high mass materials from coal-derived liquids ☆

This short paper highlights the unusual properties of the high-mass material of coal liquids isolated by their insolubility in pyridine and solubility in NMP. The separation has been achieved by a column chromatography method. One gram quantity have been processed and near quantitative recovery of the sample as fractions has been achieved. This fractionation permitted recourse to a broad range of analytical methods, including some (e.g. 13C NMR), which require large sample sizes. Multiple macro analyses have been undertaken, using elemental analysis, TGA proximate analysis, NMR and FT-ir in addition to the micro-analytical methods used previously—pyrolysis-gc-ms, SEC, UV–fluorescence, probe-ms and MALDI-ms. The fractions show increasing concentrations of large molecular mass material with increasing polarity of successive eluents used in the fractionation. Evidence from solid-state 13C NMR and UV–fluorescence spectroscopy show progressive structural changes with increasing apparent molecular mass.

Size-exclusion chromatography of large molecules from coal liquids, petroleum residues, soots, biomass tars and humic substances

Size-exclusion chromatography (SEC) using 1-methyl-2-pyrrolidinone (NMP) as eluent has been calibrated using various standard polymers and model compounds and applied to the analysis of extracts of coal, petroleum and kerogens, to petroleum vacuum residues, soots, biomass tars and humic substances. Three separate columns of different molecular mass (MM) ranges were used, with detection by UV absorption; an evaporative light scattering detector was used for samples with no UV absorption. Fractionation was useful to separate signal from the less abundant high-mass material, which was normally masked by the strong signal from the more abundant low-mass material in the absence of fractionation. Fractionation methods used to isolate high-mass materials before SEC analysis included planar chromatography, column chromatography and solvent solubility. The apparently large molecules were concentrated into the fractions not soluble in common solvents and were relatively immobile in planar chromatography. All samples and fractions contained some material excluded from the column porosity. Evidence from other techniques suggests that the excluded material is of different structures from that of the resolved material rather than consisting of aggregates of small molecules. We speculate that the excluded material may elute early because the structures of this material are three-dimensional rather than planar or near planar.

Structural characterisation of Baltic amber and its solvent extracts by several mass spectrometric methods.

A sample of Baltic amber ( approximately 40 million yrs old) has been extracted using pentane, toluene and 1-methyl-2-pyrrolidinone (NMP). The relationship between solubility characteristics of the extracts in relation to molecular mass and chemical makeup has been investigated. The extracts were first characterised by (13)C-NMR spectrometry, size exclusion chromatography (SEC) and UV-fluorescence spectroscopy. The fractions differed less in terms of chemical structural features than they did in terms of molecular mass. This contrasts markedly with data on fractions of coal-derived liquids, but parallels results from petroleum-derived vacuum residues. In SEC, the toluene soluble/pentane insoluble fraction gave a peak for high mass material at about 67 000 u. Material excluded from the column porosity in this fraction and in NMP solubles eluted between 8 and 11 min, corresponding to polystyrene masses between 200 000 and several million u. A column with a larger pore size distribution was calibrated using polystyrene and polymethylmethacrylate standards with detection by a light-scattering evaporative analyser. The largest polystyrene standard (15.4 million u) eluted at 13.4 min, similar to that of the earliest eluting amber-derived material in the NMP solubles fraction. Results from probe-MS and pyrolysis-GC/MS have been used to confirm the similarity of chemical structures of the three solubility fractions. Broadly, low mass ions appear to correspond to the various monomeric units of structures present in the amber, the higher mass ions to dimer units and the molecular ions to the different combinations of three or more monomeric units. The main monomer groups have been identified in detail, showing a situation very different from that of coal-derived materials, where the sizes of aromatic ring systems increase with molecular size.

Effect of polydispersity on the characterization of coal-derived liquids by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: inferences from results for mixtures of polystyrene molecular mass standards

Seven polystyrene molecular mass standards have been run in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) singly, in pairs, in groups of three and as a mixture of the seven distinct samples. All standards had polydispersities or near unity. When run singly or in pairs, MALDI-spectra of all standard polymer samples could be observed clearly and showed approximately equal areas. Mixtures of multiple standards have been run at variable ion extraction voltages: when the voltage was reduced below 25 kV, low molar mass samples tended to predominate in the spectra, at the expense of the higher molar mass standards. Peaks due to the high mass standards were still observable above the noise level, but (for equimolar mixtures) areas under the peaks were no longer comparable. With the full set of seven samples, discrimination against intensities of the higher mass standards could be clearly observed, even at the highest ion extraction voltage available (30 kV). With increasing ion extraction voltage the MALDI-spectra of a coal tar pitch and its tetrahydrofuran-insoluble fraction showed increasing intensities of higher mass ranges. Due to the wide polydispersity of coal derived samples, MALDI-spectra would be expected to severely underestimate the proportion of high mass materials present. Further work on mixtures of different types of polymer standards would clearly be useful; for coal derived liquids, more extensive fractionation than that used here would seem advisable in order to reduce sample polydispersity. © 1997 John Wiley & Sons, Ltd.

Cyclic polyesters: 3. Attempts to prepare catenated polymers using polymer-supported reagents

A range of reactions have been carried out using 11-bromoundecanoic acid attached to polymer supports in an attempt to prepare the first catenated polymers. In one series of reactions, cyclization of the polymer-supported polyester chains was effected in the presence of sharp fractions of polydimethylsiloxane rings, but no evidence of catenane formation could be found. Instead, a white crystalline product polyester was obtained. Its identity is discussed here. In another series of reactions, polymer-supported linear polyesters were cyclized in the presence of recycled cyclic polyesters. Gel permeation chromatographic analyses showed that substantial quantities of high molar mass material had been formed. This material may prove to be the first catenated polyesters to be prepared.

30 nm resolution zero proximity lithography on high-Z substrates

In order to fabricate masks for x-ray lithography, there is growing interest in subtractive patterning of high atomic mass (high-Z) materials such as tungsten or gold. Favorable writing speeds and sub-50 nm resolution without proximity effects combine to make heavy ion focused ion beam lithography an ideal candidate for this area of nanofabrication. Using a 50 keV Ga+ beam with an 8 nm spot diameter, we have exposed a variety of proximity effect test patterns in 60 nm thick PMMA on 0.5 μm thick tungsten films. The results indicate that 30-nm resolution or better is possible at line/space pitches as small as 80 nm. The test patterns show no apparent proximity effects at these dimensions. An anomalous ‘‘inverse proximity effect’’ was observed, and was determined to be an artifact of the scanning electron microscope technique used to observe the PMMA resist.

High mass material (&gt;104 daltons) in a coal liquefaction extract, by laser‐desorption mass spectrometry

AbstractThe use of a laser‐desorption mass spectrometer to examine a coal liquefaction extract known to contain high‐molecular‐mass material (from size‐exclusion chromatography) has shown the presence of components of molecular mass in excess of 104Da for the first time. The molecules detected differ from each other in molecular mass by a few hundred or a few thousand Da. These preliminary results indicate that the basic coal‐structure molecules probably consist of aromatic clusters on a chin, in reasonable agreement with current theories of coal structure.

Role of thermal insulation in passive designs of buildings

The utilization of solar energy for active and passive applications in buildings requires the careful selection of materials that have, (a) high thermal storage capacity, (b) thermal insulation efficiency, and (c) a balance of the two. The choice is not easy to make notably when the building falls in a temperate climatic zone. This paper tackles the selection of materials for usage in buildings from different angles to ensure the ease of selection. First, the optimal economic thickness of an insulation material is determined very accurately using the minimum life-cycle cost method and the annual heating degree days (AHDDs) for different sites. From this, the optimal thermal transmittance (U-value) for the building structure in a given climatic zone is determined. Second, a graphic relationship between U-value vs AHDDs is established. Third, annual energy savings in kWh ton−1 of insulation material is calculated. From this, the pay-back period of energy consumed in manufacturing the installed thermal insulation material is calculated. The higher the pay-back period the less desirable is the use of thermal insulation materials and more favourable is the use of high mass materials. This approach is well reasoned to allow its extensibility to all buildings in all climatic zones. It should certainly give insight to the possible contribution of solar energy in meeting demand for active and passive heating/cooling of buildings. Results are summarized in Figs 3 and 4.

High resolution depth profiling of light elements in high atomic mass materials

A novel approach to elastic recoil analysis of light elements in high atomic mass materials is presented based on time of flight detection. TOF spectra of recoils induced by 20 MeV Ar ions, after a 1 m flight path, have the unique characteristics of inverting the in-depth mass sequences, allowing such unusual depth profiling. Depth resolutions below 10 nm are reported for oxygen and carbon in heavy materials like titanium with detection limits in the order of 10 15 at/cm 2. No absorbers are required for such an analysis, for which improvements of the analyzing depth and the sensitivity are proposed.

Substrate heating in cylindrical magnetron sputtering sources

The magnetic plasma confinement in magnetron sputtering sources makes the plasma ionization process very efficient and allows high sputtering rates to be achieved with reduced substrate heating, particularly in the cylindrical-post magnetron geometry where a virtual anode separates the substrates from the plasma. Heating flux measurements at typical substrate locations surrounding cylindrical-post magnetron sputtering sources were made for the argon sputtering of seventeen metals, representing a range of atomic masses, crystallographic structures and sputtering yields. The heating flux data are combined with deposition rate measurements and are reported as energy per coating atom deposited. They are consistently interpreted in terms of four basic heating processes: (1) heat of condensation; (2) sputtered atom kinetic energy; (3) plasma radiation; (4) ion neutralization and reflection at the cathode. Ion reflection becomes increasingly important for the high mass materials. The energy per atom deposited is independent of the deposition rate and the argon pressure and varies from 15 to 25 eV atom −1 for light metals to over 50 eV atom −1 for heavy metals with moderate sputtering yields. The sputtering efficiency is shown to be a useful concept in accounting for ion reflection. Comparative data are reported for sputtering with nitrogen and oxygen and for cylindrical-hollow magnetron sources. The energy per atom is relatively high in nitrogen and oxgyen sputtering because of a high sputtering efficiency and a reduced metal sputtering yield. The closer proximity of the plasma in hollow cathodes introduces a plasma bombardment contribution to the heating flux.