INTRODUCTION - Stannous ion, Sn (II), is the most effective and widely used reducing agent in 99mTc-radiopharmaceutical cold kits. However, Sn (II) is unstable in the presence of oxygen and in aqueous solutions it can precipitate as an insoluble basic chloride or oxidize to Sn (IV) by dissolved oxygen. The quantitative determination of Sn (II) in the manufacturing process and storage of radiopharmaceutical kits is an important procedure to assure the quality during the shelf life. The Sn (II) content is usually found in the range of 30-1500 μg /vial. AIM - The aim of this work was to quantify Sn (II) and Sn(IV) in EC and ECD radiopharmaceutical cold kits by differential pulse polarography during expiration time (12 months). METHODS - EC and ECD contain 0.300 and 0.125 mg of SnCl2 2H2O, respectively, in each vial formulation. The analysis was performed using a dripping mercury electrode 150 polarographic/stripping analyzer with a conventional 3-electrode configuration. The experimental conditions were 1s drop time, 50 mV s-1 scan rate, -50 mV pulse amplitude, 40 ms pulse time and 10 mV step amplitude. The supporting electrolytes for Sn (II) and Sn (IV) determinations were 3 mol L-1 H2SO4 and 3 mol L-1 HCl, respectively. A differential pulse polarogram of the supporting electrolyte was obtained in the range of -200 to -800 mV before and after 5 successive additions of 20 μL of 1,000 μg mL-1 Sn(II) or Sn(IV) standard solution into the cell, and the polarographic waves of 0, 2.0, 4.0, 6.0, 8.0 and 10.0 μg mL-1 tin concentrations were recorded. The maximum current (μA) of the waves (peak height) was used to obtain the analytical curve and quantify Sn (II) and Sn (IV) in the cold kits. Taking part of the stability studies, 3 different batches of EC and ECD were analyzed up to 12 months. The samples were reconstituted with 1 mL of deaerated purified water and 100, 320, 80 and 20 μL aliquots were added into the cell to determine Sn (II) and Sn (IV).

RESULTS - The polarographic method was adequate to quantify Sn (II) and Sn(IV) in EC and ECD cold kits during manufacture and storage. There was no significant variation among the replicates.

CONCLUSION - All the results for Sn (II) content into the EC or ECD vial were in the acceptable limits guaranteeing the 12 month expiration time.