[en] HDEHP is used as the metal ion extractant in an extractive scintillator solution for the assay of alpha emitters. In this application it is necessary that the HDEHP be as color-free as possible to minimize quenching in the scintillator and as free of monoalkyl phosphoric acid and polyphosphates as possible. HDEHP was purified by various methods: copper precipitation, vacuum distillation, caustic scrubbing. The results are presented. (U.K.)