http://hl7.org/fhir/StructureDefinition/SubstanceAmount|4.0.1

Base StructureDefinition for SubstanceAmount Type: Chemical substances are a single substance type whose primary defining element is the molecular structure. Chemical substances shall be defined on the basis of their complete covalent molecular structure; the presence of a salt (counter-ion) and/or solvates (water, alcohols) is also captured. Purity, grade, physical form or particle size are not taken into account in the definition of a chemical substance or in the assignment of a Substance ID.