Selective polarographic determination of stannous ion in technetium radiopharmaceutical cold kits

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.

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-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 H(2)O(2) was performed. The calibration curves for Sn(II) and Sn(IV) were obtained in the range of 0-10 μg·mL(-1).

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 (μA) = 0.098 [Sn(II)] + 0.018 (r(2) = 0.998) and i (μA) = 0.092 [Sn(IV)] + 0.016 (r(2) = 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 (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 -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.

The developed polarographic method was adequate to quantify Sn(II) and Sn(IV) in DMSA, ECD, MDP, and pyrophosphate cold kits.