selectivity ratio

https://doi.org/10.1351/goldbook.S05569
Synonymous with selectivity coefficient.
Source:
PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2386 (https://doi.org/10.1351/pac199365112373)