Ionization methods, mass series

Prest HE. 1999. Ionization methods in gas phase mass spectrometry operating modes of 5973Network series MSDs. Agilent technologies. Application Note (23), 5698-7957E, www.agilent.com/chem. 

The traditional approach to drag discovery is based on rational drag design. Lead compounds, often structurally derived from natural products, are synthesized one at a time and are further optimized by a series of synthesis and screening steps. An important aspect is the structural characterization of reaction intermediates and end-products. MS and, given the nature of mai r of the compounds involved, LC-MS can play an important role in this. Often, molecular-mass determination with a soft ionization method leads to sufficient answers to the synthetic chemists. 

Figure 1. Schematic diagram showing a TRU-spec extraction chromatography method for separation of uranium, thorium, protactinium, and radium from a single rock aliquot. Further purification for each element is normally necessary for mass spectrometric analysis. Analysis of a single aliquot reduces sample size requirements and facilitates evaluation of uranium-series dating concordance for volcanic rocks and carbonates. For TIMS work where ionization is negatively influenced by the presence of residual extractant, inert beads are used to help remove dissolved extractant from the eluant.

Agilent GC-MS ChemStation System equipped with capillary gas chromatograph HP 5972,5973, or 6890 series Agilent 6890 series autosampler. The GC-MS system is operated in the positive-ion, electron-impact ionization mode. Chromatographic parameters of the acquisition method are listed in Table 3.1.7. TIC is recorded over the mass range m/z 50-550, and the total run time is 33 min. 

In the process of developing PRMs, it is necessary to study and establish measurement methods which are used to analyzed the purity of raw gases and verify the stability of the gas mixture kept in the cylinder. Up to now, NRCCRM has been equipped with several series of analytical techniques including atmospheric pressure ionization mass spectrometer, gas chromatograph, infra-red spectrophotometer with long-path gas cell, chemiluminescent, non-dispersive infra-red, minor 02 and H20 analyzer and so on. 

Mass spectrometric studies on a series of pyrylium perchlorates by both electron ionization (El) and fast atom bombardment (FAB) methods showed that only some compounds give the expected formation of Py+ and/or [Py-H]+ ions, and this is followed by extensive fragmentation. Under FAB conditions, all the compounds show the formation of Py+ without fragmentation products <1994RCM163>. 

U-series nuclide activities can be measured directly by detection of their emitted nuclear particles, e.g., alpha particle counting by solid-state detectors (Ivanovich and Harmon, 1992). In contrast, measurements by mass-spectrometry do not require waiting for Nature to take its course. Atoms of the sample are ionized and accelerated so that charged particles of the nuclides themselves can be measured by Faraday cups or electron multipliers (see Goldstein and Stirling, 2003). Mass-spectrometry is hence a more rapid technique. Typically mass-spectrometry measurements take tens of minutes to hours, while counting methods require days to weeks. 

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