Mass Spectral Databases for El

El mass spectra are excellently reproducible when measured under standard conditions (70 eV, ion source at 150-250°C, pressure in the order of 10 Pa). This is not only the case for repeated measurements on the same instrument, but also between different types and brands of mass spectrometers. Large El mass spectral libraries exist in either printed [73-75] or digitized form [76]. The most comprehensive El mass spectral databases are the NIST/EPA/NIH Mass Spectral Database and the Wiley/NBS Mass Spectral Database [77-80]. 

Searching for a mass spectrum of an unknown substance in a mass spectral database often very quickly identifies the unknown, provided the corresponding spectrum is already available in the database. However, even if this is not case, the search might deliver similar spectra of closely related compounds, thus facilitating structure elucidation [81]. 

Formula Searches spectra corresponding to a chemical formula. Parentheses are resolved, e.g., CH3CH(C(CH3)3)2 is converted to C10H22-Constraints like name fragment or certain peaks can be selected. 

Molecular weight Searches for spectra belonging to a defined molecular weight. Constraints like elements, required peaks etc. may be selected. 

Any peaks A search based on a small number of peaks. Spectra can be searched using the largest peaks, or peaks in certain ranges of total intensity. 

Note Although similarity searches generally provide useful search results, it is always necessary to cross check the hits from the database. Even the highest score hit can be wrong. Some interpretational skills will be advantageous. .. 

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