Selective Polarographic Determination of Stannous Ion in Technetium Radiopharmaceutical Cold Kits

Abstract

The aim of this work was to develop a selective method for quantification of Sn(II) and Sn(IV) in dimercaptosuccinic acid (DMSA), ethylcysteinate dimer (ECD), methylenediphosphonic acid (MDP), and pyrophosphate radiopharmaceutical cold kits by differential pulse polarography. Methods: A dripping mercury electrode 150 polarographic/stripping analyzer with a conventional 3-electrode configuration was used with 3 M H₂SO₄ and 3 M HCl supporting electrolytes for Sn(II) and Sn(IV), respectively. The polarographic analysis was performed using a 1-s drop time, 50-mV·s⁻¹ scan rate, −50-mV pulse amplitude, 40-ms pulse time, and 10-mV step amplitude. To quantify Sn(IV), oxidation of Sn(II) by H₂O₂ was performed. The calibration curves for Sn(II) and Sn(IV) were obtained in the range of 0–10 μg·mL⁻¹. Results: The analytic curves for Sn(II) in 3 M H₂SO₄ and Sn(IV) in 3 M HCl were represented by the following equations: i (μA) = 0.098 [Sn(II)] + 0.018 (r² = 0.998) and i (μA) = 0.092 [Sn(IV)] + 0.016 (r² = 0.998), respectively. The detection limits were 0.21 μg·mL⁻¹ for Sn(II) and 0.15 μg·mL⁻¹ for Sn(IV). In DMSA, ECD, MDP, and pyrophosphate, 90.0%, 64.9%, 93.2%, and 87.5%, respectively, of the tin was present as Sn(II). In this work, selective determination of Sn(II) and Sn(IV) was achieved using 2 supporting electrolytes (H₂SO₄ and HCl). In 3 M H₂SO₄, only Sn(II) produced a polarographic wave with the maximum current in −370 mV. Under the same conditions, no current could be determined for Sn(IV). In 3 M HCl, Sn(II) and Sn(IV) were electroactive and the maximum currents of the 2 waves appeared in −250 and −470 mV. No other components of the lyophilized reagents had any influence. Conclusion: The developed polarographic method was adequate to quantify Sn(II) and Sn(IV) in DMSA, ECD, MDP, and pyrophosphate cold kits.