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

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A low-temperature coal tar has been fractionated by column chromatography into acetonitrile, pyridine and 1-methyl-2-pyrrolidinone- (NMP) solubles. The tar and its fractions have been examined by pyrolysis-gas chromatography/mass spectrometry (GC/MS). Fractionation by planar chromatography was also carried out for purposes of comparison. Molecular masses of the fractions were estimated by size-exclusion chromatography (SEC), and bulk structural characterisation was carried out by (13)C-NMR and UV-fluorescence spectrometry. SEC showed that the fractions shifted to progressively shorter elution times (higher apparent masses) with diminishing solubility, i.e. from acetonitrile to NMP solubles. UV-fluorescence spectra showed parallel shifts to longer wavelengths and lower fluorescence quantum yields, indicating increasing sizes of aromatic ring systems and increasingly complex molecules. GC/MS analysis of the tar showed alkanes from C10 to C32 and extensive series of alkylated aromatics, phenols, indenes, naphthalenes, phenanthrenes and fluoranthenes. Pyrolysis-GC/MS results for the acetonitrile solubles closely resembled the data for the tar sample, with extensive series of alkylated benzenes, phenols and naphthalenes as well as alkanes from C16 to C28. The pyridine-soluble fraction showed no significant aromatic pyrolysis products and only relatively weak signals for alkanes between C16 and C27. The NMP-soluble fraction showed even less overall signal, with no significant aromatic components and weak signals for alkanes between C21 and C25, even though (13)C-NMR analyses showed that approximately half of the carbon detected was aromatic. The aliphatics are assumed to provide bridging structures between polycyclic aromatic (PCA) ring systems.

contrasting

confidence: 89%

Pyrolysis‐gas chromatography/mass spectrometry of fractions separated from a low‐temperature coal tar: an attempt to develop a general method for characterising structures and compositions of heavy hydrocarbon liquids

Islas

Suelves

Carter

et al. 2002

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“…Fractions between 50–60 min would therefore be expected to contain a component of high‐mass material as well as increasing amounts of smaller MM material. This valley to zero intensity between excluded and retained peaks in SEC has been observed for many different materials20,, 21 and may represent a shift from small near planar molecules below mass 3000 u, to three‐dimensional structures at higher masses.…”

Section: Resultssupporting

confidence: 52%

“…It may be noted that, when similar analytical methods were applied to fractions of an extract of Baltic amber (fossilised resin), the data did not show increasing polynuclear aromatic ring systems with increasing molecular mass 21. Murchison's work,22 quoted by Given,23 suggests that aromatic structures gain prominence in resinites of bituminous coals (i.e.…”

Section: Low‐temperature Tarmentioning

confidence: 96%

See 1 more Smart Citation

Pyrolysis‐gas chromatography/mass spectrometry of pitch fractions recovered from preparative size exclusion chromatography: structural differences with increasing molecular size

Islas

Suelves

Carter

et al. 2002

Self Cite

A sample of high-temperature coal tar pitch has been fractionated by preparative scale size exclusion chromatography (SEC). Twenty-four fractions corresponding to narrow molecular mass distributions were collected at sequential elution times of 3 minutes. The preparative scale column is thought to have filtered out most of the very large molecular mass material and the analysis focused on smaller mass components. The recovered fractions were characterised by analytical SEC. Pyrolysis-gas chromatography/mass spectrometry (pyrolysis-GC/MS) of the fractions was used to evaluate changes in main structural features with changing molecular size.As expected, analytical SEC of the fractions showed a systematic shift to smaller molecular sizes with increasing elution time. UV-fluorescence spectra of the samples showed parallel structural shifts to shorter wavelengths and gains in intensity with increasing elution times. Pyrolysis-GC/MS showed parent polycyclic aromatic components considered typical of pitch. The major fragments detected were pyrenes and fluoranthenes (m/z 202) and chrysenes (m/z 228). Benzopyrenes (m/z 252) and larger aromatics were not prominent amongst the pyrolysis products. Taken together, molecular structures were found to change significantly from fraction to fraction, but no systematic pattern emerged with changing elution time. Some components were identified as having formed during the analytical pyrolysis procedure itself. As aromatic products larger than dibenzopyrene (m/z 302) would not elute from the column, detected fragments are thought to have detached from larger pitch molecules.The pyrolysis of the largest species gave only alkanes and alkenes, with the aromatic fragments thought to be too large to elute through the GC column. The work provides information regarding the aromatic groups that are readily lost from larger molecules. Larger aromatic structures are thought to condense (to char) during the analytical pyrolysis step; the method is limited in not being able to provide information about their structural features.

“…Following reports4–6 on the investigation of amber of different origin by various instrumental approaches, we thought it of interest to undertake an exhaustive study based on the most recent mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), on eight different amber samples of different age and geographical origin.…”

mentioning

confidence: 99%

Mass spectrometry in the characterization of ambers. I. Studies of amber samples of different origin and ages by laser desorption ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry

Tonidandel¹,

Ragazzi

Roghi

et al. 2008

Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers.