The fraction or percentage (
R%) of the total quantity of a substance extracted (usually into the organic solvent phase) under specified conditions. Specifically, R A = Q A Q A ', where Q A ' and Q A are the original and final quantities of the substance A. This term is not recommended. fraction extracted should be used.
Sources:
Orange Book, 2nd ed., p. 90 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2385 (https://doi.org/10.1351/pac199365112373)