The distribution coefficient (partition coefficient) \(K_D\) in solvent extraction is defined as: \(K_D = \dfrac{[\text{solute}]_{\text{organic}}}{[\text{solute}]_{\text{aqueous}}}\) — the ratio of the concentration of solute in the organic (extracting) phase to its concentration in the aqueous phase at equilibrium. A high \(K_D\) means preferential distribution into the organic phase.