enrichment factor, Sin liquid-liquid distribution

The factor by which the ratio of two substances in the feed must be multiplied to give their ratio after treatment.

$Q A Q B = S A,B Q A ' Q B '$

where $Q A$ and $Q A '$ are the final and initial amounts of species A and $Q B$ and $Q A '$ are the final and initial amounts of species B. Hence $S A,B = E A E B$ where $E$ is the fraction extracted. In terms of $D$ , $n$ , $r$ (where $n$ is the number of stages and $r$ the phase ratio),

$S A,B = 1 − ( 1 + r D A ) − n 1 − ( 1 + r D B ) − n$

Source:

PAC, 1993, 65, 2373 (Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)) on page 2382

Orange Book, p. 90