Other Uses of Databases

In addition to using spectra databases to identify molecules, databases also offer other possibilities. 

A database also allows instant access to the spectrum of a molecule by searching its name or CAS (Chemical Abstract Service) number. Suppose we must verify immediately that water has not been contaminated by toluene. We plan to use a GC-MS coupling device equipped with a quadrupole. The best way to proceed is by injecting toluene to determine its retention time (under the correct chromatographic conditions) and the main ions of its mass spectrum. One must then analyze the water (after liquid-liquid extraction with an organic solvent or directly by solid phase microextraction coupled with GC-MS) in SIM on the two or three main ions of toluene to reach a limit of detection that is as low as possible. If toluene cannot be injected in the laboratory, quick access to its El spectrum is available in databases. Ions for SIM acquisition will then be chosen from the reference spectrum. 

One can interrogate a database in several ways. For example, a database can be asked to show all the spectra of compounds corresponding to a raw formula or a given molecular weight One can also make it display mass spectra showing a base peak at m/z 250 and another peak at m/z 300 whose relative abundance ranges from 50 to 60% of that of the base peak. 

Certain databases propose programs to help with the interpretation of mass spectra. This is a conunercial argument to seduce new users. The programs are totally inefficient for the reasons explained in Chapter 9. 

Budzildewicz, H., C. Djerassi, and D. H. Williams. 1967. Mass Spectrometry of Organic Compounds. San Francisco Holden Day. 

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