An attribute of a substance which may be distinguished qualitatively and determined quantitatively. In the context of analytical chemistry, the attribute may refer to a physical quantity such as X- or γ-ray energy, or it may refer to a measure of amount such as mass or concentration.
PAC, 1995, 67, 1699
(Nomenclature in evaluation of analytical methods including detection and quantification capabilities (IUPAC Recommendations 1995))
on page 1701