Removing micronutrient metal cation interferences prior to titrimetric determination of polyphosphate chain length

Abstract

Evaluntion of chain lengths of polymeric phrosphates is essential for the characterization of polyphosphate-based fertilizers. The titrimetric method, which is the most reliable and simple means of determining number average chain lengths (n), cannot be applied to solutions containirrg micronutrtrient ions. In this investigation, methods have been purposed for the elimination of metal ion interference prior to the titrimetric determination of the average chain length of polyphosphate solutions. When Cu2+, Fe3+, Mn2+, Mg2+ or Mo6+ are present the solutions, solvent extraction of their complexes with 8-hydroxyquinoline at appropriate pH, prior lo titration, was very eflective. The interference due to Zn2+ was conveniently masked by the addition of potassium ferrocyanide and the titration carried out in the presence of the insoluble complexes. These methods do not introduce any perceptrure additional error in the determination of n. They cab also be conveniently combined when more than one interfering ion is present in the polyphosphate solution. These methods, therefore, offer a rapid, simple, and reliable means tor analyzing micronutrient polyphosphate fertilizers.