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99mTc radiopharmaceuticals are widely used in medical imaging diagnostic procedures. They can help to diagnose a large number of diseases affecting the bones and major organs of the body such as the heart, brain, liver, kidney, and thyroid.

99mTc radiopharmaceuticals are usually prepared from so-called «cold kits». A cold kit consists of the ligand to which 99mTc is complexed, a reducing agent, a buffer, stabilizers, and further ingredients. Sn(II) is a typical reducing agent. It reduces the Tc(VII) that is added to the cold kit to a lower oxidation state which then forms the stable organic complex.

For quality control, the Sn(II) content has to be determined in the kit vial. Sn(II) can be selectively determined using differential pulse polarography. The freeze-dried content of the vial is dissolved in diluted nitric acid prior to determination. 

Polarography is a straightforward, sensitive, selective, and interference-free method for the determination of mg/L levels of Sn(II) in radiopharmaceuticals.

Cold kit for preparation of sodium pertechnetate (99mTc) injection.

884 Professional VA
Figure 1. 884 Professional VA

After dissolving and diluting the sample with nitric acid supporting electrolyte, the polarographic determination of Sn(II) is carried out on the 884 Professional VA with the Multi-Mode Electrode pro as working electrode using the parameters listed in Table 1. The concentration of Sn(II) is determined by three additions of Sn(II) standard addition solution.

Table 1. Parameters
Parameter Setting
Working electrode DME
Mode DP – Differential Pulse
Start potential -0.22 V
End potential -0.66 V
Peak potential Sn(II) -0.35 V
  • Working electrode: Multi-Mode Electrode pro with standard glass capillaries
  • Reference electrode: Ag/AgCl/KCl (3 mol/L) reference electrode with electrolyte vessel. Bridge electrolyte: KCl (3 mol/L)
  • Auxiliary electrode: Platinum rod electrode

The determination of Sn(II) in cold kits for sodium pertechnetate (99mTc) injection can be carried out in a simple and straightforward manner. The method is selective and free of interferences. It is suitable for concentrations in the mg/L range.

Figure 2. Determination of Sn(II) in a 99mTc injection preparation kit with 3 standard additions.
Table 2. Result
Sample Concentration [mg/L]
99mTc injection preparation kit 22.1
  1. International Atomic Energy Agency, Technical Report No. 466 «Technetium-99m Radiopharmaceuticals: Manufacture of Kits», Vienna, 2008
  2. Zolle, Ilse (Ed.), Technetium-99m Pharmaceuticals Preparation and Quality Control in Nuclear Medicine, Springer, 2007

Metrohm AG

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Internal reference: AW VA CH4-0566-082017