Evaluating electron ionization mass spectral library search results

As the size of various collections of electron ionization mass spectra gets larger, there is a continuing and increasing propensity to rely on the results of computerized library searches. The results of these computerized searches do not necessarily account for a spectrum that is produced by the mixture of two or more different compounds. Sometimes the submitted spectrum is not that of a compound whose spectrum is in the library. The quality of the spectrum submitted to the library is often such that the numerical confidence level reported for the search result is so low that it will cause the result to be disregarded. When the sample spectrum is matched against library spectra that have been condensed, the search result can be misleading. Three different examples of mass spectral search results are examined: one, with a high confidence level that the unknown has been identified, but the results are incorrect; one, where the spectrum of the unknown compound is not in the library; one, where consideration of the numerical search results would cause a positive identity not to be confirmed.