Statistical evaluations of the effects of five matching parameters on the probability of retrieving a correct answer with the probability based matching (PBM) system have been made. Combining the resulting values found In matching an unknown spectrum makes It possible to rank retrieved reference spectra according to the predicted match reliability. This ranking substantially improves the performance of PBM, and the reliability value Is especially helpful In avoiding the assumption that the best matching spectrum represents the correct compound when Its spectrum Is actually not in the reference file. Quadratic scaling of the abundance values of the unknown compensates for spectral differences caused by Instrumental variations, a critical problem In matching reference spectra. Other improvements Include a more effective "flagging" technique to remove spurious reference peaks. Extensive applications with a commercial GC/MS system have demonstrated the Increased effectiveness made possible by these PBM modifications.

technique is one of convenience since the fluorescence lifetime instrumentation can be used. This allows the cancellation of errors due to geometry or quenching in the calculation of the natural lifetime, T~, by T / @ Q = T~. The method does demonstrate that accurate quantum yields can be measured by using pulsed source excitation in the single photon counting mode.The method as presented here could benefit from certain instrumental improvements, such as monitoring the lamp intensity or a simultaneous measurement of absorbance and fluorescence. This would provide further precision and convenience by eliminating the manual change from absorbance to the fluorescence configuration. This could be accomplished in a manner similar to that of Holland et al. (5). This technique holds promise for the performance of routine quantum yield measurements and easy automation because of the intrinsic digital form of the data. A "spectrum-stripping" technique allows Improved identlflcation of minor mixture components in matching unknown mass spectra against a large reference file using the "Probabllity Based Matchlng" (PBM) system. The poor quantitative agreement expected between spectra of the same compound run under different condttions can be compensated by the hlgh information content of the mass values. Such spectrum subtraction Is complementary to the "reverse-search" feature of PBM, being especially valuable for identlfylng component spectra containing a number of peaks common to other components of the sample.

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