Polarographic determination of edetate disodium in eyewash and ophthalmic decongestant solutions

The quantitative analysis of edetate disodium in nonprescription eyewash and ophthalmic solutions is described. The method involves differential pulse polarography using a dropping mercury electrode. A known concentration of cadmium or zinc is added to a buffer in a polarographic cell. The sample solution is incremented into the cell with a micropipet. The peak current decreases because the resulting chelate is not reducible at the potentials used. The quantity of edetate disodium in the sample then is determined graphically. Some contact lens cleaning and wetting solutions containing polymeric compounds are amenable to assay to edetate disodium if extraction, precipitation, centrifugation, or dilution steps minimize the maximum suppressor effect of the additives. These steps are very effective with cellulose ether compounds but are ineffective with polyvinyl alcohol.