Determination of sequestration capacities of iron control chemicals

Titrimetry with electronanalytical endpoint detection was used to determine sequestration capacities of polyphosphates for Fe2+ and Fe3+. These methods have the advantage of directly monitoring sequestration of the metal ions. Potentiometry with a divalent ion ion-selective electrode was used to monitor sequestration of Fe2+; polarography was used to monitor sequestration of Fe3+. Four commercial liquid polyphosphate formulations, a Zn-orthophosphate, a silicate formulation, two solid polyphosphates, and pyrophosphate were studied. No significant difference was found in sequestration capacities for either metal ion among the polyphosphates. Polyphosphates were found to sequester only about 14% as much Fe2+ as Fe3+. The polarographic titration affords an efficient, precise method of studying factors affecting sequestration of iron by polyphosphates.