Polarographic determination of Sn(II) in samples containing Sn(IV) such as in 99m-Technetium radiopharmaceutical kits

A sensitive, alternative method to titrimetry or spectrophotometry for the evaluation of tin(II) ions (0–5 μg ml−1) in matrices containing tin(IV) ions was investigated. Differential pulse polarography was chosen. The supporting electrolyte was a buffer solution 0.7M NaF/0.1 M NaNO3/0.1 M HEPES at pH 8. The potential was swept from −500 to −800 mV vs. Ag/AgCl/ saturated KCl, using a dropping mercury electrode with a drop time of 1 s, a sweep rate of 4 mVs−1, a differential modulation with a pulse time of 40ms, a delay time of 20ms, a measurement time of 20ms and a pulse amplitude of −50 mV. In technetium labelling kits, containing medronic acid (methylenediphosphonic acid), 10−3 M ZnCl2 was added to the supporting electrolyte in order to eliminate the interference of medronic acid. This polarographic method is suitable for the determination of Sn(II) in samples containing Sn(IV) with or without medronic and ascorbic acid.