Tetrasodium pyrophosphate decahydrate (4.46 g, 10 mmol) was dissolved in the minimum amount of water (about 50 mL) and passed through a column of AG50W X8 resin (100-200 mesh, 4×10 cm bed) poured in water. The column was eluted with water and the eluent was collected in an ice-cooled flask until pH of the eluent approached neutrality. Tri-n-butylamine (Aldrich Gold Label, 7.1 mL, 30 mmol) was added to the eluent and the two phases were stirred vigorously until all of the amine dissolved. The resulting solution was lyophilized. The residue was co-evaporated twice with dry pyridine and once with dry dimethylformamide. The residue was dissolved in dry dimethylforamide (10 mL) and the resulting 1.0 M solution was stored (for as long as one month) at 0° under argon until used.
