https://doi.org/10.1351/goldbook.S06073
Amount-of-substance of a component divided by the mass of the system.
Notes:
- The term component is recommended for clinical chemistry, ISO uses 'substance'.
- The term system is recommended for clinical chemistry, ISO uses mixture.
- Use of the term level as a synonym for content is deprecated.
- In describing a quantity, content must be clearly differentiated from concentration.