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 H 2 SO 4 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-mVÁs 21 scan rate, 250-mV pulse amplitude, 40-ms pulse time, and 10-mV step amplitude. To quantify Sn(IV), oxidation of Sn(II) by H 2 O 2 was performed. The calibration curves for Sn (II) and Sn(IV) were obtained in the range of 0-10 mgÁmL 21 . Results: The analytic curves for Sn(II) in 3 M H 2 SO 4 and Sn(IV) in 3 M HCl were represented by the following equations: i (mA) 5 0.098 [Sn(II)] 1 0.018 (r 2 5 0.998) and i (mA) 5 0.092 [Sn(IV)] 1 0.016 (r 2 5 0.998), respectively. The detection limits were 0.21 mgÁmL 21 for Sn(II) and 0.15 mgÁmL 21 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 (H 2 SO 4 and HCl). In 3 M H 2 SO 4 , only Sn(II) produced a polarographic wave with the maximum current in 2370 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 2250 and 2470 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. Radi opharmaceutical cold kits for labeling with 99m Tc contain Sn(II) for reduction of technetium to lower oxidation states that are chemically reactive to specific ligands. Besides these ligands, the cold kits usually contain stannous chloride (SnCl 2 ) and different additives (complexing agents, antioxidants, and buffers). The amount of stannous ions varies (0.03-1.5 mg of SnCl 2 ), although a minimum concentration must be present to guarantee the lyophilized reagent shelf life and to allow efficient labeling with 99m Tc (1).Depending on the medium composition, Sn(II) ions in low-concentration solutions (,2.0Á10 24 M) are oxidized, and the formation of basic complexes takes place above pH 2.00 (2,3). The quantitative determination of Sn(II) in radiopharmaceutical cold kits is an important aspect of quality control, and the analytic method must be accurate even in the presence of Sn(IV) ions (4).Such techniques as colorimetry, titrimetry, spectrophotometry, voltammetry, and polarography have been described in the literature for Sn(II) determination in cold kits (5-12).Zimmer et al. studied the formation of a red porphyrin complex in the presence of Sn(II) ions using a colorimetric method....
