An enlarged data base of electron-ionization mass spectra.

The computer-searchable data base of reference mass spectra described earlier has been increased in size by 76%, so that it now contains 139,859 different spectra of 118,144 different compounds. The average number of peaks per spectrum is 53. All spectra were examined for errors by the Probability Based Matching (PBM) and the Quality Index (QI) algorithms and by human inspection. An improvement to the QI algorithm is based on the Terwilliger suggestion concerning saturated spectra. The number of different elemental compositions of compounds has increased by 64%. By using unknowns from the original data base with PBM, the probability that these incorrectly match a new spectrum is only 33% of that of incorrectly matching a spectrum in the original data base, further demonstrating that the variety of data in the library has been substantially expanded. Including additional reference spectra (measured under different conditions) of the same compound in the data base reduced the proportion of incorrect best-matching spectra by 42%.