The ratio of the total mass of a solute in the extract to that in the other phase.
It is the product of the (concentration) distribution ratio and the appropriate phase ratio.
It is synonymous with the concentration factor or mass distribution ratio, this latter term being particularly apt.
The term concentration factor is often employed for the overall extraction factor in a process or process step.
PAC, 1993, 65, 2373
(Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993))
on page 2384
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook