Mass spectrometry with spectral libraries

W. Ion suppression effects in liquid chromatography-electrospray-ionization transport-region collision induced dissociation mass spectrometry with different serum extraction methods for systematic toxicological analysis with mass spectral libraries. J Chromatogr B 2002 773 47-52. 

Most commonly used is the recording of UVA IS spectra, which are compared with spectral libraries. However, more informative is the recording of a FTIR- or Raman-spectrum in situ. These relatively recent developments to measure diffuse reflectance can now be carried out routinely. The in situ employment of MS after TLC detection is described in detail elsewhere (see Chapter 9, Thin Layer Chromatography Coupled with Mass Spectrometry), as well as the employment of radioactively labelled substances (see Chapter 12, Thin-Layer Radiochromatography). 

Maximum benefit from Gas Chromatography and Mass Spectrometry will be obtained if the user is aware of the information contained in the book. That is, Part I should be read to gain a practical understanding of GC/MS technology. In Part II, the reader will discover the nature of the material contained in each chapter. GC conditions for separating specific compounds are found under the appropriate chapter headings. The compounds for each GC separation are listed in order of elution, but more important, conditions that are likely to separate similar compound types are shown. Part II also contains information on derivatization, as well as on mass spectral interpretation for derivatized and underivatized compounds. Part III, combined with information from a library search, provides a list of ion masses and neutral losses for interpreting unknown compounds. The appendices in Part IV contain a wealth of information of value to the practice of GC and MS. 

A common method for identification of organic compounds is mass spectrometry (MS) in combination with GC. After separation of the component by GC the mass spectrometer transform the analyte into gaseous ions in vacuum in the ion source. For electron impact ionization this results in different mass fragmentation patterns with different mass-to-charge ratios (m/z). From this fragmentation pattern it will be possible to identify the compound by comparison with commercial mass spectral libraries. Identification of unknown compounds can be facilitated by... 

To many, mass spectrometry is synonymous with El mass spectrometry. This view is understandable for two reasons. First, historically, El was universally available before other ionization methods were developed. Much of the early work was El mass spectrometry. Second, the major libraries and databases of mass spectral data, which are relied upon so heavily and cited so often, are of El mass spectra. Some of the readily accesible databases contain El mass spectra of over 390,000 compounds and they are easily searched by efficient computer algorithms. The uniqueness of the El mass spectrum for a given organic compound, even for stereoisomers, is an almost certainty. This uniqueness, coupled with the great sensitivity of the method, is... 

The common procedure to generate silylated pyrolysates is to perform pyrolysis in a filament system followed by off-line derivatization with BSTFA. The chromatographic separation was done on a DB-5 column (60 m long, 0.32 mm i.d., 0.25 pm film thickness) using a temperature gradient between 50° C and 300° C with detection by mass spectrometry. The compounds identified by mass spectral library search in the pyrograms from Figures 12.3.3 and 12.3.4 are listed in Table 12.3.2. 

It is often difficult to determine the degree to which the chemistry proceeded on the entire library population and whether peaks in a mass spectrum are due to the product, side reactions, reagents, solvents, or impurities. Diversity Sciences developed mass-spectral methods to distinguish all components that are cleaved from a solid support and implemented the method into the analytical construct. While early studies demonstrated promising results for fragmentation methods with tandem mass spectrometry (MS/MS), stable isotopes were routinely implemented as signature peaks for the identification of compounds that are produced from solid-phase reactions [27]. 

Part Mass Spectrometry by A. N. Davies gives an overwiew from a user s point of view. Commercially available mass spectral databases and software products for library searches are characterized. A statement from section 24.1 is repeated here because it seems to be essential not only for mass spectral database systems "... let the people who will be working with the systems have a major say in the testing and selection of the product to be purchased. .. . 

NIST have produced a freely available package called AMDIS (automated mass spectrometry deconvolution and identification system) for the analysis of GC/MS data sets. Developed to assist in the task of verifying the international Chemical Weapons Convention (http //www.opcw.org/) financially supported by the US Defense Special Weapons Agency (DSWA, US Department of Defense) the AMDIS program is also distributed with the NIST 02 Mass Spectral Library (see above). 

Each of the aromatic compounds analysed was identified by means of its retention time, coeluted with a standard solution of the commercial product and confirmed by mass spectrometry (Hewlett-Packard 5972 MSD, Palo Alto, CA, USA). Positive ion electron impact mass spectra were acquired in scan mode, with a range of nVz 39-300 and a scan-rate of 1.6 scan s-i. For each compoimd the mass spectra was confirmed by comparison with the Wiley mass spectral library. The chromatographic column, injector and oven temperatures, carrier gas and its flow, were the same as those used for the quantification, as described below. 

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