collected in a sterile 5 mL product vial. *2.5. [89Zr]Zirconium-Oxalate Characterization*

### *2.5. [89Zr]Zirconium-Oxalate Characterization* 2.5.1. Determination of Radionuclidic Purity

2.5.1. Determination of Radionuclidic Purity The radionuclidic purity of 89Zr was determined by gamma-spectroscopy using a high purity germanium (HPGe) detector (Ortec, Oak Ridge, TN, USA). A 4-h scan of a diluted aliquot (50–80 kBq) was performed at the end of purification. To determine longer-lived contaminants, scanning was The radionuclidic purity of <sup>89</sup>Zr was determined by gamma-spectroscopy using a high purity germanium (HPGe) detector (Ortec, Oak Ridge, TN, USA). A 4-h scan of a diluted aliquot (50–80 kBq) was performed at the end of purification. To determine longer-lived contaminants, scanning was repeated after three half-lives.

#### repeated after three half-lives. 2.5.2. Determination of Effective Specific Activity

2.5.2. Determination of Effective Specific Activity The effective specific activity (MBq/µmol) of 89Zr was determined by labeling *p-SCN-Bz-*DFO with purified [89Zr]zirconium oxalate. *p-SCN-Bz-*DFO was selected as it is a commonly used chelator for labeling antibodies with 89Zr [17,18]. Specific activity was calculated for three consecutive batches The effective specific activity (MBq/µmol) of <sup>89</sup>Zr was determined by labeling *p-SCN-Bz*-DFO with purified [89Zr]zirconium oxalate. *p-SCN-Bz*-DFO was selected as it is a commonly used chelator for labeling antibodies with <sup>89</sup>Zr [17,18]. Specific activity was calculated for three consecutive batches of [89Zr]zirconium oxalate. A stock solution of *p-SCN-Bz*-DFO in DMSO (1 mg/mL) was prepared

of [89Zr]zirconium oxalate. A stock solution of *p-SCN-Bz-*DFO in DMSO (1 mg/mL) was prepared and

and 15 reaction tubes were prepared by 1:2 serial dilution in ultrapure water (500 µL) to give a final *p-SCN-Bz*-DFO concentration in the range of 2.07E-02 to 1.267E-06 µmol. A solution of [89Zr]zirconium oxalate was neutralized with the 2 M NaCO<sup>3</sup> (pH 7 ± 0.2) and added to the *p-SCN-Bz*-DFO solutions. The resulting solutions were incubated at 37 ◦C on a shaker at 650 RPM for one hour. After incubation, 1 µL aliquots were spotted on iTLC and analysed by using citrate buffer (100 mM, pH 5.0) as a mobile phase. iTLC plates were measured using radio-TLC scanner. The results of the *p-SCN-Bz*-DFO titration with <sup>89</sup>Zr were plotted and fitted with a sigmoidal dose-response curve to generate an EC<sup>50</sup> value which was used to calculate specific activity in MBq/µmol.
