Identity confirmation of 99m Tc-MAG3, 99m Tc-Sestamibi and 99m Tc-ECD using radio-LC-MS Tom Verduyckt 1 , Davy Kieffer, Dieter Huyghe, Bernard Cleynhens, Kristin Verbeke 2 , Alfons Verbruggen, Guy Bormans * Laboratory of Radiopharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, University of Leuven, Herestraat 49, B-3000 Leuven, Belgium Received 24 April 2002; received in revised form 5 March 2003; accepted 7 March 2003 Abstract Due to the low concentrations in which 99m Tc-radiopharmaceuticals are obtained (4  /40 ng/ml), confirmation of the identity of these tracer agents in the European Pharmacopoeia is generally performed only indirectly by assessment of their retention times on RP-HPLC. We have investigated whether it is possible to obtain more direct proof of the identity of technetium-99m labelled radiopharmaceuticals using radio-LC-MS. As representative examples, negatively charged 99m Tc-MAG3, positively charged 99m Tc-Sestamibi and neutral 99m Tc-ECD were used. The three technetium- 99m radiopharmaceuticals were prepared in several conditions to obtain variable relative amounts of radiochemical impurities and variable concentrations of the complexes (pico- to nanomolar). The preparations were analyzed on a reversed phase C18 HPLC column using a radio-LC-MS system equipped with a time of flight mass spectrometer with electrospray ionization in positive( 99m Tc-Sestamibi, 99m Tc-ECD) or negative( 99m Tc-MAG3, 99m Tc-ECD) mode. For each of the studied complexes, the main peak in the radiometric channel coincided with the expected molecular ion mass of the corresponding technetium complex in the mass spectrometer channel. The relative error on the measured accurate mass was in the range of 10 ppm. The identity of several radiochemical impurities of the three technetium complexes was also confirmed or established. It is concluded that radio-LC-MS can be a sensitive aid in quality control of ‘no carrier added’ radiopharmaceuticals. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Radio-LC-MS; Radiopharmaceutical; 99m Tc-MAG3; 99m Tc-Sestamibi; 99m Tc-ECD; HPLC 1. Introduction Technetium-99m ( 99m Tc) is the most frequently used radionuclide for in vivo imaging studies in Nuclear Medicine. It owes its popularity to its nearly ideal physical characteristics (i.e. short physical half-life (T 1/2 ) of 6 h; g energy of 140 keV; no particulate emission during decay) and * Corresponding author. Tel.:  /32-16-343-738; fax:  /32-16- 343-891. E-mail address: guy.bormans@uz.kuleuven.ac.be (G. Bormans). 1 Grant-holder of the Flemish Institute for promotion of scientific /technological research in the industry (IWT). 2 Postdoctoral Fellow of the Fund for Scientific Research, Flanders, Belgium. Journal of Pharmaceutical and Biomedical Analysis 32 (2003) 669  /678 www.elsevier.com/locate/jpba 0731-7085/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0731-7085(03)00174-2