Besides these traditional spectral libraries for untargeted metabolomics that focus on fragmentation data, other libraries that include complementary information or for different data acquisition methods are starting to become available. For example, some spectral libraries contain LC retention time information as well , such as the METLIN small molecule retention time dataset . Additionally, with the increasing integration of ion mobility functionality in modern mass spectrometry instruments, ion mobility libraries that contain reference collision cross section (CCS) measurements are emerging . This availability of retention time and CCS reference measurements provides orthogonal information for metabolite annotation from untargeted MS/MS data. Additionally, spectral libraries for alternative data acquisition methods exist. For example, mzCloud organizes MSn spectra into "fragmentation trees," and the METLIN-MRM spectral library is a multiple-reaction monitoring (MRM) transition repository for small-molecule quantitative mass spectrometry that contains MRM transitions for more than 15,500 unique molecules .