The METLIN Metabolite and Chemical Entity Database[1][2][3] is the largest repository of experimental tandem mass spectrometry[4] and neutral loss[5] data acquired from standards. The tandem mass spectrometry data on over 930,000 molecular standards (as of December, 2023)[6][7][8][9][10] is provided to facilitate the identification of chemical entities from tandem mass spectrometry experiments. In addition to the identification of known molecules, it is also useful for identifying unknowns[3] using its similarity searching technology.[11] All tandem mass spectrometry data comes from the experimental analysis of standards at multiple collision energies and in both positive and negative ionization modes.
METLIN[12] serves as a data management system to assist in metabolite and chemical entity identification by providing public access to its repository of comprehensive MS/MS and neutral loss data.[7][3][5] METLIN's annotated list of molecular standards include metabolites and other chemical entities, searching METLIN can be done based on a molecule's tandem mass spectrometry data, neutral loss masses, precursor mass, chemical formula, and structure within the METLIN website. Each molecule is linked to outside resources such as the Kyoto Encyclopedia of Genes and Genomes (KEGG) for further reference and inquiry. The METLIN database was developed and is maintained solely by the Siuzdak laboratory at The Scripps Research Institute.