Radiofrequency cavity ion source in solids mass spectrometry

Abstract

Kerogen presumably forms early during sedimentation, locking into its matrix biological debris, which is subsequently reduced. Kerogen, therefore, becomes not only immobilized with respect to migration; but the system is closed to outside contamination subsequent to formation.Kerogen is potentially the most reliable source of biological precursor information.A number of questions come to mind. Which of the two fractions reflects more faithfully the relative abundance of pentacyclic terpanes precursors originally laid down in this sediment?The extractable fraction presumably has been modified by maturation; whereas, the kerogen presumably does not change much with time but could be greatly modified by pyrolysis. But, does pyrolysis modify the relative abundance of surviving biomarkers with respect to those originally present in the kerogen matrix?It is difficult to answer these questions. Note from Figure 1 that the 5-ring C27 and C29 terpanes, which are of low abundance in the extractable fraction, are, relatively speaking, dominant in the pyrolysis fraction.The first impulse is to suggest that the c 2 7 and C29 terpanes are a product of pyrolysis, i.e., pyrolytic loss of bridgehead or gem-dimethyls from, say, a C30 terpane. There are a t least two reasons why this is probably not the case. First, the negligible concentration of Cas terpanes is not consistent with a statistical ihermodynamic loss of labile C1 or C2 groups from a C30 or higher terpane. Further, the (228 terpane found in the pyrolysis oil is a very specific one, Le., unusually long retention times, also found at very low levels in the bitumens solvent extract fraction of Green River shale. No other cz8 terpanes are detected in either fraction.The second reason that comes to mind is that the complete mass spectra of the terpanes found in the pyrolysis oil show no evidence for unusual methyl loss phenomenon; i.e., the bridgehead and gem-dimethyl are apparently in place, a t least as far as the A/B rings are concerned. In other words, the mass spectra look perfectly normal compared to known terpanes. This is also verified by the unusual fact that all terpanes found on the extract fraction are also found in the pyrolysis fraction, apparently without exception.The only conclusion, it seems, is to say that the terpanes which have survived pyrolysis rather than those extracted reflect more faithfully the distribution and identity of terpanoids originally laid down in the sediment. LITERATURE CITED(1) R. H. Dott and M.A radiofrequency discharge in argon is used to sputter and ionize solid samples for analysis. Metals machined to act as a cavity electrode can be analyzed directly. Samples may also be deposited from solution for subsequent elemental analysis of the residues. The rf discharge allows analysis of both conductors and nonconductors. A glass electrode is used as a cavity electrode for application of multielement solutions. The precision obtainable by electrical scans was about f10% RSD. Lowest detection limit is -10-100 ng.

Glow Discharge Mass Spectrometry

“…It is observed that the first prototypes, in which hollow-cathode DC and RF GDs were coupled to SFMS, were developed by Harrison et al, in the 1970s. 59,60 Since then, there has been a tremendous improvement in technology resulting in the development of several powerful and versatile instruments that are nowadays commercially available. Each of these instruments has a particular design of the GD ion source and power supply.…”

“…60,108,109 It should be mentioned that up to now a commercial RF source is only available for the Autoconcept GD90. However, no publication is known showing results, so far.…”

Radiofrequency glow-discharge devices for direct solid analysis

“…In 1975 Donohue and Harrison [83] developed a radiofrequency cavity ion source enabling mass spectral characterisation of thin films from dried solution samples. They reported similar spectra and analytical sensitivity using dc or rf hollow cathode discharges.…”

New hardware for radio frequency powered glow discharge spectroscopies and its capabilities for analytical applications

“…More recently the field of application was extended to nonconducting materials by rf powered glow discharges [3][4][5]. Unfortunately, this mode is not as easy to handle as the dc mode and developments are still in progress.…”