REMOVING MICRONUTRIENT METAL CATION INTERFERENCES PRIOR TO TITRIMETRIC DETERMINATION OF POLYPHOSPHATE CHAIN-LENGTH

Evaluation of chain lengths of polymeric phosphates is essential for t he characterization of polyphosphate-based fertilizers. The titrimetri c method, which is the most reliable and simple means of determining n umber average chain lengths ((n) over bar), cannot be applied to solut ions containing micronutrient ions. In this investigation, methods hav e been proposed for the elimination of metal ion interference prior to the titrimetric determination of the average chain length of polyphos phate solutions. When Cu2+, Fe3+, Mn2+, Mg2+, or Mo6+ are present in t he solutions, solvent extraction of their complexes with 8-hydroxyquin oline at appropriate pH, prior to titration, was very effective. The i nterference due to Zn2+ was conveniently masked by the addition of pot assium ferrocyanide and the titration carried out in the presence of t he insoluble complexes. These methods do not introduce any perceptible additional error in the determination of (n) over bar. They can also be conveniently combined when more than one interfering ion is present in the polyphosphate solution. These methods, therefore, offer a rapi d, simple, and reliable means for analyzing micronutrient polyphosphat e fertilizers.