Separation of 99mTc by saline elution
The growth of 99mTc in the radionuclide generator reaches a maximum at about 23 hours from the original condition where only atoms of 99Mo are present. The chemical form of the parent 99Mo is such that it is strongly bound to the alumina in the column. The chemical form of the daughter however allows it to be easily washed from the column using sterile isotonic saline.
All generator systems in common use for production of 99mTc provide for the repeated elution of this radionuclide by the passage of an isotonic saline solution over an alumina column with collection of the eluted material in an appropriate shielded container. The isotonic saline solution is generally drawn slowly through the column by the use of a vacuum in the collection (product) vial. For details of the elution process see Elution. Although great care is taken to obtain a product free from all unwanted impurities it is imperative that a series of checks and controls are in place to confirm the identity and purity of the eluted 99mTc. Among the impurities that may be encountered are aluminium ions from the alumina column, 99Mo due to "breakthrough" of the parent radionuclide, other radionuclidic impurities that arise due to the method of production and purification of the parent 99Mo, radiolysis products, pyrogens, and microorganisms. Although not considered an impurity, there will also be varying amounts of 99Tc as a "carrier", which will influence the specific activity of the final products (also see Product issues with eluted 99mTc).