speciation

in chemistry
https://doi.org/10.1351/goldbook.ST06861
Distribution of an element amongst defined @[email protected] in a system.
Source:
PAC, 2004, 76, 1033. (Glossary of terms used in toxicokinetics (IUPAC Recommendations 2003)) on page 1070 [Terms] [Paper]
This definition replaces an earlier definition of speciation.