Purify the pyrophosphate by chromatography on Whatman No 1 paper using tert-butyl alcohol/formic acid/water (20:5:8, RF 0.60) or 1-propanol/ammonia/water (6:3:1. RF 0.48). Alternatively purify it by chromatography on a DEAE-cellulose column or a Dowex-1 (formate form) ion-exchanger using formic acid and ammonium formate as eluents. A further purification step is to convert it to the monocyclohexylammonium salt by passage through a column of Dowex-50 (cyclohexylammonium form) ion-exchange resin. It can also be converted into its lithium salt.