For some ions, a mix of conformers or tautomers may be present, each with distinct IR spectra (Figures and), which may be addressed by optimizing linear combinations of computed vibrational spectra 48 . However, this is not pursued here, as it would severely slow down the evaluation of spectral similarities and likely give poorer performance for metabolites that exhibit a "pure" population. Moreover, the benefits are likely small as mixtures are not frequently observed (<15% based on manual inspection) and minimally affect the IR spectrum when the contribution of the minor population is small (Figure ). Methods that experimentally deconvolute the mixtures, e.g. by separating conformers so tautomers with ion mobility spectrometry or by employing 2-color laser experiments , could improver heir identification analogous to using spectra of multiple adducts.