The fraction or percentage (R%) of the total quantity of a substance extracted (usually into the organic solvent phase) under specified conditions. Specifically, $R_{\text{A}}=\frac{Q_{\text{A}}}{{\left(Q_{\text{A}}\right)}^{{}^{\prime }}}$, where ${\left(Q_{\text{A}}\right)}^{{}^{\prime }}$ and $Q_{\text{A}}$ are the original and final quantities of the substance A. This term is not recommended. Fraction extracted should be used.