About a 4-fold increase in radioactive concentration of Tc was obtained (cf. approximately 10-12 ml normal saline is required for the elution of Tc from the gel column). Generators containing up to 22.2 GBq (600 mCi) Mo in 6-7 g ZrMo gel column (35 x 13 mm) were prepared and a radioactive concentration of Tc up to 4 GBq x ml (110 mCi x ml) was obtained on the first day of use. The overall recovery of Tc was >90%, Mo breakthrough was 10 to 10% and the duration of concentration was 3-5 min. The chemical impurity in terms of Al, Mo and Zr was <10 ppm each. The same procedure for the concentration of pertechnetate was applied to generators with 12-15 g ZrMo gel beds to obtain a higher capacity Tc gel generator, with similar findings.

m Tc gel generator / Zirconium molybdate / Hospital radiopharmacy evaluation / Microwave drying / Centralized radiopharmacy Summary As a sequel to the process standardization for small scale production of " m Tc gel generators based on zirconium molybdate-"Mo, extensive evaluation of the generator performance including for clinical use was carried out and is reported here. Following the procedure standardized by us earlier, 9 lots of "Mo were converted into ZrMo gel adopting aseptic practices and two different techniques for drying the ZrMo cake -heated air at 60-80 °C and microwave drying at 385 watts. 14 generators, containing up to 18.5 GBq "Mo, supplied for clinical use and evaluated at two hospital radiopharmacies showed satisfactory generator performance. The applicability for preparing larger capacity generators for centralizeid radiopharmacies and feasibility to achieve reduced process time and ease of control by using microwave oven drying have also been established.

We report on the preparation and evaluation of a large size (jumbo) alumina column (approximately 40 g, 90 x 20 mm) chromatographic generator and post-elution concentration of 99Tcm using a single column of a weak anion exchanger. The generator was eluted with approximately 40 ml of a modified single salt buffer solution of 1:1 v/v 0.025 M or 0.05 M NH4OAc:0.7 M AcOH. This eluate was then passed through a small column of DEAE cellulose, a common weak anion exchanger, to trap 99TcmO4-, which was recovered by elution in 6 ml of normal saline. This amounts to a 5- to 7-fold increase in radioactive concentration (RAC) of 99Tcm, when compared to the RAC on direct elution with normal saline from the same jumbo alumina column generator. The overall yield of 99Tcm was in the range of 70-90%. 99Mo breakthrough was 10(-3)-10(-4)%, radiochemical purity was > 98%, and chemical purity, in terms of Al and Mo content, < 10 ppm each. The compatibility of pertechnetate obtained by this method for preparing 99Tcm labelled formulations such as Tc-MDP and 99Tcm-ethyl cysteinate dimer was found to be satisfactory. These promising results open up the feasibility of using (n, gamma) 99Mo adsorbed on a large (40-60 g) alumina column as a relatively more user-friendly source of 99Tcm in comparison to methyl ethyl ketone extraction, and as a producer-friendly process in comparison to the zirconium molybdate gel method.

The effect of subtle variations on zirconium molybdate-Gels exhibiting optimum characteristics were found to be formed at a pH of 4-5 by reacting [Zr]:[Mo] in the mole ratio of 1.25:1 and after drying, the product was dispersed into granules by disintegration with normal saline.

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