The effectiveness of combining spectra of different adducts is best illustrated with acetylglycine (HMDB0000532), for which the individual adducts rank 10 th ([M-H] -), 20 th ([M+H] + ) and 6 th ([M+Na] + ) in an unsupervised search, but combined they rank 1 st (Table ). Decomposition of Figure into the individual adducts shows that the [M+H] + adducts are retrieved best from the library, followed by