STPP or sodium triphosphate is an inorganic compound with the formula Na5P3O10. STPP, sodium tripolyphosphate is the sodium salt of the penta-anion polyphosphate, which is the conjugate base of triphosphoric acid. Sodium tripolyphosphate is produced by heating a stoichiometric mixture of disodium phosphate, Na2HPO4, and monosodium phosphate, NaH2PO4, under carefully controlled conditions. Sodium tripolyphosphate stpp.