Use of Molecular Weight and Elemental Composition as an Additional Constraint in Library Search

Abstract

Identification of organic compounds based only on searching against electron ionization mass spectral libraries is tentative. To increase the reliability of the identification, additional information should be used. Gas chromatographic retention indices, in addition to mass spectra, are most often used. Molecular weight and elemental composition is less frequently used, because additional experiments are required to determine these characteristics. In the present paper, we examined the influence of the molecular weight, elements present in a molecule and molecular formula on the results of the library search. It is shown that, determination of the nominal mass or molecular formula slightly increases efficiency of the library search (for example, probability that the correct compound occupies the first position in the list of possible candidates increases by only 2.8 and 3.0% respectively). On the other hand, use of additional constraints in the library search can significantly reduce the number of possible candidates and simplify predicting the absence of compound in the database.