An investigation of aspects of radiochemical purity of ^99mTc-labelled human serum albumin nanocolloid.

Nanocolloidal human serum albumin radiolabelled with <sup>99m</sup> Tc provides a diagnostic radiopharmaceutical for sentinel node lymphoscintigraphy. NanoHSA (Nanotop), a commercially available kit, enables the simple preparation of this radiopharmaceutical via reconstitution with pertechnetate eluted from a generator. Thin-layer chromatography is widely used for determining radiochemical purity in clinical nuclear medicine. Quality control methods recommended by the manufacturer were sometimes reported to yield variable results. Therefore, we proposed and evaluated three alternative thin-layer chromatography methods for the quality control of [ <sup>99m</sup> Tc]Tc-NanoHSA from a commercially available kit. The radiochemical purity of [ <sup>99m</sup> Tc]Tc-NanoHSA determined with all methods was reproducible and met the requirements of the SPC and the European Pharmacopoeia (≥ 95%). Our quality control using iTLC-SG chromatographic paper in methyl ethyl ketone mobile phase identified only free pertechnetate as impurity, resulting in > 99% RCP. The quality control using iTLC-SG in 85% methanol or iTLC-SA in 0.9% NaCl identified an additional small fraction of a hydrophilic impurity, resulting in 95-97% RCP. Glucose was identified as a potential <sup>99m</sup> Tc-carrying hydrophilic species contributing to hydrophilic impurities. Our quality control of [ <sup>99m</sup> Tc]Tc-NanoHSA with non-polar mobile phase tended to underestimate the amount of hydrophilic impurities, although without compromising the final quality of the radiopharmaceutical. Alternative TLC methods using aqueous mobile phases enabled a more accurate determination of hydrophilic impurities