Identification by means of a spectral library

Species identification through comparison of spectra is employed in numerous analytical fields. Several software packages are used to conduct searches in spectral libraries in which the main peaks of known compounds are encoded. The compounds offering the best matches are retained as potential candidates, ranked in order of decreasing similarity with an index of 0 to 1000. 

The National Institute of Standards and Technology (NIST) Mass Spectral Library is the most widely used mass spectral reference library, which presently contains a collection of about 200 000 electron impact (El) mass spectra verified 

when one considers the number of chemicals which is perhaps in excess of 10 million, whereas the largest of the databases of mass spectra contain some 200000 chemicals, the need to employ other techniques is obvious. In this way, and coexisting with the development of databases some software packages use the concept of artificial intelligence methods to determine chemical structures from their mass spectra. In a number of cases these techniques based upon programmable criteria, chemical classification of the unknown, rarity of mass etc. appear to work well, but are limited to particular classes of compounds. The problem lies in the fact that unknowns are more often totally unknown (such as in environmental samples). 

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