Table 1 Definitions of key terms used in the best practice guidelines and reporting standards

Metabolomics

Systematic study of endogenous metabolites and the biochemical processes that they are involved in, within a cell, tissue, or organism.

Endogenous metabolite

Precursor, intermediate, or a product of metabolic biochemical reaction, produced by the host cell or organism.

Untargeted toxicokinetics

Measurement of the absorption, distribution, metabolic biotransformation, and/or excretion of a chemical specifically as part of an untargeted metabolomics toxicity study.

Untargeted

Analytical assay in which the analytes are not predefined and are typically unidentified during initial data acquisition. The approach attempts to measure the broadest range of endogenous metabolites possible. The assay is semi-quantitative.

Targeted

Analytical assay in which the analytes are predefined and identified to MSI level 1 (see supplementary note 11). The assay can be quantitative or semi-quantitative.

Semi-targeted

An assay which combines both targeted and untargeted approaches. Some analytes will comprise a targeted panel (identified to MSI level 1), but the remaining data is acquired and treated as untargeted. The approach attempts to measure the broadest range of endogenous metabolites possible. The assay is at least semi-quantitative.

Semi-quantitative

An assay in which only relative amounts of each analyte can be compared—e.g. a given analyte may be twice the concentration in one sample than another, though the absolute concentrations are not known.

Quantitative

An assay resulting in absolute concentration information for each analyte (e.g. in M or μg/L).

Quality assurance

A set of procedures that are done in advance of analysis and that are used to improve the quality of data.

Quality control (QC)

A set of activities that a laboratory does during or immediately after analysis that are meant to demonstrate the quality of project data.

System suitability QC

QC sample type used to demonstrate the analytical system is fit for purpose and working within specification.

Intrastudy QC (previously termed pooled QC)

QC sample type used within one study with multiple purposes, primarily to assess (and potentially correct for) intrastudy reproducibility.

Intralab QC

QC sample type used within one laboratory to assess (and potentially correct for) any differences between separate studies.

Interlab QC

QC sample type used across multiple laboratories to assess (and potentially correct for) any differences between laboratories.

Process blank

QC sample type used to measure any interfering signals (i.e. contaminants) that may arise from the ‘process’, e.g. extraction, such that these contaminant signals can be removed from a dataset.