Mass spectrometry (MS) is the primary analytical approach in untargeted metabolomics due to its high sensitivity, selectivity and throughput. Routine analyses of complex biological samples yield large numbers of detected features -numbers that are unrivalled by other analytical techniques . Subsequent (biological) interpretation requires the precise molecular identification of the m/z features of interest . Herein lies the major challenge of MS-based metabolomics, as little structural information is contained in an m/z value alone. To distinguish between structural isomers, MS is often hyphenated with gas or liquid chromatography (GC or LC), tandem MS (MS/MS) or ion mobility spectrometry (IMS) . Annotation is then achieved by comparison against libraries with reference MS/MS spectra , retention times or CCS values . Yet, despite the many reference libraries, detailed molecular identification remains the main bottleneck in MS-based metabolomics.