Rapid determination of the radiochemical purity of ^99mTc- antimony trisulfide colloid prepared by standard and alternative heating methods

The purpose of this study was to validate a rapid quality control method for the lymphoscintigraphy tracer ^99mTc-antimony trisulfide colloid (^99mTc-ATC). Methods: ATC was labeled with ^99mTc according to the manufacturer's instructions as well as by alternative heating conditions designed to provide a range of percentages of radiochemical purity (RCP): the tracer was prepared in a dry block heater with heating cavities of different sizes, the temperature of the heating block was varied from 70°C to 115°C, or the duration of heating was varied from 15 to 35 min. Anion-exchange minicolumns were Mailed to separate any ^99mTc- pertechnetate impurity from ^99mTc-ATC with physiologic saline as the eluent. Quality control results were compared with the results from the manufacturer's recommended method, which uses an instant thin-layer chromatography (ITLC) strip with saline as the migrating solution. Results: The quality control results obtained with a cartridge method in 2-3 min compared favorably with those obtained with the ITLC method with saline when the tracer was prepared by heating at 115°C in a dry block heater for 35 min (RCPs, 99.4% ± 0.3% [mean ± SD] and 99.2% ± 0.3%, respectively; n = 25). The cartridge and ITLC quality control results also were in excellent agreement (correlation coefficient, 0.99) over a range of RCPs (80%-100%). An alternative anion-exchange cartridge that was tested in this study was not suitable for assaying the RCP of ^99mTc-ATC because of the complete retention of ^99mTc-pertechnetate on the sorbent. Conclusion: Compared with the established ITLC method, the cartridge quality control method tested in this study is rapid and provides a reliable assessment of the RCP of ^99mTc-ATC. For the preparation of ^99mTc-ATC, a dry block heater can be successfully substituted for a boiling water bath and is recommended for heating at high altitudes.