Dissolve it in aqueous Me2CO and allow crystallisation to proceed slowly; otherwise very small crystals are formed. No trace of Me2CO is left in the crystals after drying at 120o [Davies & Staveley Trans Faraday Soc 53 19 1957]. Also, the salt can be precipitated from a dilute AcOH solution of sodium tetraphenylborane in the presence of NHions. After standing for 5minutes, the precipitate is filtered off onto a sintered porcelain crucible, washed with very dilute AcOH and dried at room temperature for at least 24hours [Vendlandt Anal Chem 28 1001 1956]. Alternatively a solution of sodium tetraphenylborane (5% excess) in H2O is added to NH4Cl solution. After 5minutes the precipitate is collected, washed several times with H2O and recrystallised from aqueous Me2CO. [Howick & Pflaum Analyt Chim Acta 19 342 1958, Beilstein 16 IV 1625.]
