For each accession number, file paths and metadata were requested via the MetaboLights API. Afterward, equivalent metadata columns were matched between MTBLS and ReDU. For example, "NCBITaxonomy'' was matched to "Organism", "UBERONBodyPartName'' to "Organism part", "Instrument" to "MassSpectrometer" and so on. MTBLS already uses publicly controlled ontologies allowing easy matching to ReDU ontology. For ReDU columns where no equivalent predefined column was present in MTBLS, we attempted to find the equivalent columns via the non-default column names the submitter employed. For example, to retrieve the ReDU variable "BiologicalSex" we looked at whether a factor column "sex" or "gender" was deposited. If the same spectral raw file was available in multiple formats, only the open format (.mzML or .mzXML) was kept.