METLIN

METLIN is a large, publicly accessible metabolite database of tandem mass spectrometry (MS/MS) data. It is maintained by the Scripps Research Institute and is widely used in metabolomics and related fields to identify metabolites from MS and MS/MS experiments. The database comprises experimental MS/MS spectra for a broad range of metabolites, typically linked to chemical structures, accurate masses, and, where available, metadata about measurement conditions such as ion mode and collision energy.

Users search METLIN by precursor mass, molecular formula, or by matching MS/MS fragmentation patterns to experimental spectra. The resource supports data from multiple ionization modes and collision energies, enabling more robust identification of unknown compounds. Data are derived from analyses of authentic standards and, in some cases, high-confidence predictions are used to expand coverage. METLIN also provides guidance on spectral interpretation, including common fragment ions and neutral losses, to assist in structural annotation.

Access to METLIN is provided through a web portal that generally requires user registration. The database is widely used in academia and industry for untargeted metabolomics, targeted validation, and small molecule identification in drug discovery and natural products research. METLIN is frequently cited as a reference for metabolite spectral data and serves as a foundation for spectral matching workflows in mass spectrometry-based studies, often in combination with complementary databases and software tools.