Extraction-Polarograpy Applied to the Microdetermination of Phosphate

Abstract

Phosphate ion can be polarographically determined by adding a known amount of molybdate and measuring the diffusion current due to the reduction of the excess molybdate. This method, however, is disadvantageous to the spectrophotometric one, because the polarographic procedure is less sensitive and interfered by several other constituents. In the present study a new method is developed in which the phosphate ion is extracted as phosphomolybdate into methyl isobutyl ketone and to the organic extract is added aqueous electrolyte solution and methylcellosolve, resulting in a homogeneous solution, in which the hexavalent molybdenum shows prominent and well-defined a.c.polarographic peaks. Fujinaga and others, employed a ternary mixture of chloroform-hydrochloric acidmethylcellosolve system as a polarographic . electrolyte-solvent and succeeded elegantly in the microdetermination of lead by means of diethyldithiocarbamate extraction. In the present study the Takeuchi-Ishii method for the phosphomolybdate extraction into methyl isobutyl ketone was utilized and the polarographic behavior of molybdate ion in the ternary electrolyte-solvent composed of methyl isobutyl ketone, methylcellosolve and an aqueous solution of various electrolytes is investigated. The a.c. polarographic method by Breyer has shown in this case an excellent result. Thus, about hundred microgram quantity of phosphate can easily be determined a.c. polarographically after the phosphomolybdate extraction.