Solution grown organic crystals are usually affected by organic and inorganic impurities, which make difficult the achievement of optimised crystalline and optical properties. For this reason, organic materials must be subjected to specific treatments before being used in crystal growth process. Here, we report on a systematic study in which different techniques (recrystallisation, solvent extraction, complexation by usual chelants) have been used to prepare crystal growth quality material for NMU. Purification process has been assisted by analysis of HPLC, UV-VIS absorption, ICP-MS and fluorescence. Results show that appropriate sequential treatments can largely improve the material purity as directly verified in the crystal growth process, where a remarkable increase of growth stability has been observed.