The correlation between spectral similarity and structural similarity for the whole validation set is visualized by plotting the average structural similarity between each reference metabolite and the ranked library structures, where the reference metabolites themselves are removed from the data (Figure ). On average, a clear increase in structural similarity is observed when approaching rank 1, with a steep increase for the ~50 best matches. Inspection of the individual structure vs spectral similarity plots (see SI) suggests that the correlation between structural similarity and spectral similarity for some metabolites is limited by the number of structural analogues present in the library (e.g. Figure in the SI). An expansion of the library to include more metabolites would therefore not only allow for the direct identification of more metabolites, but also make unsupervised searches more sensitive to substructure, as more structural analogues would be included.