Bounds for molecular weights of organic compounds from low resolution mass spectra

Simple empirical rules for determining the upper and lower limits to the molecular weight of organic compounds from low resolution mass spectra have been established and evaluated. The rules are based on the average of two easily determined spectral features, Maxmass and Himax1. The lower limit is this average less 5 Da and the upper limit is the average plus 100 Da. These limits have been evaluated with a set of 400 randomly chosen NIST/NIH/EPA reference spectra, with 400 pharmaceutically related spectra from a Swiss data base and with 100 bromine- and chlorine-containing NIST reference spectra. In only 12 cases were the true molecular weights lower than the estimated lower limits and these were due to contaminated spectra. The upper limit rule includes 98% of the spectra of all volatile compounds tested and 96% of all compounds tested.