Radiochemical purity of short-lived technetium 99m from commercial suppliers.

Abstract

Three major radiopharmaceutical firms supply separated short-lived 99mTc as sterile sodium pertechnetate, ready for use in brain scans. For small laboratories whose work loads do not justify buying a generator, this “instant” technetium is very convenient. Within the territory covered by the various firms' delivery arrangements, material ordered before 2 P.M. is usually delivered before 8 A.M. the next day. In the spring of 1968 one of these firms announced that it would have to make a 20 per cent shift in its 99mTc calibration in order to be consistent with the calibrations of other suppliers and major laboratories across the country. In a small series of spot-checks on two suppliers (including this one), no indication of such a large discrepancy had been observed here. During the summer and fall of 1968, a series of tests was carried out on routine shipments of 99mTc from all three firms. These tests involved careful calibration comparisons using conventional dilution technics, as well as determinations of the type and level of radiochemical impurities present. The calibration checks, carried out well after the 20 per cent shift previously mentioned, found the three firms agreeing within 7#x00B1; 5 per cent. The results of the radiochemical purity determinations were quite surpnsmg. The impurity pattern consistently observed in material from two of the three commercial suppliers has apparently not been reported in the scientific literature. The Atomic Energy Commission regulations specify that 99mTc must not contain more than 0.1 per cent 99Mo or 0.01 per cent 103Ru, 132Te, or 131I. No other radionuclides are mentioned specifically by the AEC, but a 99mTc product containing less than 0.01 per cent of total radioactive contaminants is generally considered readily attainable (1). Literature reports on the purity of the 99mTc obtained from 99Mo produced by neutron irradiation mention 99Mo levels far below 0.1 per cent, and “traces” of other nuclides (2). The older fission product 99Mo tended to have more types of radiochemical impurities and at higher levels than the neutron-irradiated material. The three firms selling “instant” 99mTc all use 99Mo produced by the (n,γ) reaction. Materials And Methods The materials investigated here were samples taken from routine shipments of “instant” 99mTc from the three commercial suppliers. A 1.00 cc aliquot was transferred from the manufacturer's sterile bottle to a tightly capped typical 0.5-inch diameter plastic vial. The gamma spectra were obtained with the plastic vial containing the 1 cc sample sitting on the face of a 2 × 2-inch scintillation crystal.