Revealing hidden information in GC-MS spectra from isomeric drugs: chemometrics based identification from 15 eV and 70 eV EI mass spectra

•Drug isomers can be differentiated through their conventional 70 eV EI mass spectra.•However, low energy 15 eV ionization can provide more informative mass spectra.•PCA-LDA models reveal intrinsic ring-isomer selectivity in mass spectra.•Focus on diagnostic ions or mass range selection further enhances selectivity.•Methods can be compared and optimized using a Likelihood Ratio approach.