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IMPROVED METHOD FOR ESTIMATING MOLECULAR WEIGHTS OF VOLATILE ORGANIC COMPOUNDS FROM LOW RESOLUTION MASS SPECTRA
Citation:
Scott, D. IMPROVED METHOD FOR ESTIMATING MOLECULAR WEIGHTS OF VOLATILE ORGANIC COMPOUNDS FROM LOW RESOLUTION MASS SPECTRA. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-92/133 (NTIS PB92166685).
Description:
An improved method of estimating molecular weights of volatile organic compound from their mass spectra has been developed and implemented with an expert system. he method is based on the strong correlation of MAXMASS, the highest mass with an intensity of 5% of the base peak in a mass spectrum, with the true molecular weight. inear corrections to MAXMASS, which yield molecular weight estimates, were derived empirically using the expert system. The system is based on a sequential modular design with primary classifier linked to molecular weight estimators for the resulting six classes. hese are non-halobenzenes; chlorobenzenes; bromoalkenes/alkenes; mono- and dichloroalkanes/alkenes; tri-, tetra- and pentachloro-alkanes/alkenes; and others. erformance tests were made with the old and improved expert systems and the Self Training Interpretive and Retrieval System (STIRS) on NIST reference spectra of the 10 training compounds; on a set of 32 test NIST reference spectra of other compounds found in air samples; on a set of 100 randomly selected NIST reference spectra; and on 2 spectra taken from actual field gas chromatography/mass spectrometry samples. he average absolute value deviations from the true values for the old and new expert system an STIRS were, respectively, 3.1, 1.0 and 11.6 mass units for training spectra and 13.3 13.4 and 7.1 for test spectra. or field GC/MS spectra these were 6.0, 4.3 and 10.8 an for random spectra 15.5, 16.0 and 7.5. The expert system is very fast and will run on personal computers.