QUANTIFICATION OF ISOMERIC DIFFERENCES IN MASS-SPECTRA

Several indices have been developed to characterize isomeric differenc es, degree of isomerization and spectral similarity in mass spectra. A n index (S), based on absolute value distance, is developed to describ e the similarity of two spectra. Two indices (alpha and beta) were dev eloped to characterize the maximum degree of isomerization between two isomers under mass spectrometric conditions, Another index was derive d from the former ones to characerize differences between spectra (D). The effect of random errors (i.e. reproducibility) on these indices w as also checked. Comparison of spectra of various pairs of isomers ind icated that the developed formulae are efficient for isomer characteri zation. The same indices can be used, not only for comparing isomers, but also for the quantitative comparison of complex mixtures (based ei ther on mass spectra or on chromatograms).