In solvent extraction processes, organic phase impurities can negatively impact separation factors, hydrolytic performance, and overall system robustness. The resulting inconsistent performance can affect the process-level viability of a separation concept, and thus knowledge of the impurities present, their effects on the process, and how to remove them are vital. Deleterious impurities may be introduced into a system from reagent synthesis, or result from degradation via radiolysis and hydrolysis during use. In this work, the acidic extractant, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP])-proposed for application in extractive processes aimed at separating trivalent minor actinides from lanthanides and other fission products-is characterized with respect to its common impurities and their impact on Am(III) stripping in the Actinide Lanthanide SEParation (ALSEP) system. To control impurities in HEH [EHP], existing purification technologies commonly applied for the acidic organophosphorus reagent were assessed and a new chromatographic purification method specific to HEH [EHP] is presented.