UPLC-HRMS/MS analysis allows a greater level of molecular detail to be inspected by separating the geochemical DOM background across a wide elution period, albeit without finely detailed chromatographic resolution , and enabling determination and annotation of truly resolvable metabolite features . In Table , the number of features found in TRM-0522 in positive and negative mode UPLC-HRMS and UPLC-HRMS/MS are presented. A variety of resolvable features were found over a wide range of retention times and masses, numbering 233 (negative) and 261 (positive). Unlike the typical broadly eluting features found in the geochemically degraded DOM background, these features are well resolved and can be used as reference peaks for method development, validation, and drift correction if TRM-0522 is included in metabolomics datasets. The number of library hits found using GNPS molecular networking was surprisingly low (only 5 per ionisation mode, and most of these known laboratory contaminants). This may be due to the fact that so much of DOM is not characterised and annotated , and may also be due to the extraction method used here being poor at retaining particularly hydrophilic compounds. Possibly, the pipeline and gravel filtration method used to collect coastal water for the aquarium activities at the research site also filters out many known metabolites. However, hundreds of resolvable features were found at the MS1 and MS2 level (Figure ), they simply were not matched to known compounds.