Radiochemical purity testing for 99Tcm-exametazime: a comparison study for three-paper chromatography

The standard radiochemical purity (RCP) determination uses a three-paper chromatography strip and solvent system (TP). The involvement of multiple strips for calculation of percentage primary, lipophilic 99Tcm-exametazime complex is tedious and time-consuming. The significant streaking of radioactivity on the ITLC/SG MEK strip of the TP method indicates that ITLC/SG MEK may not be an ideal system for RCP analysis of 99Tcm-exametazime. This study was undertaken to compare the standard TP method with two other proposed single-strip chromatography systems: Whatman 17 Chr paper with ethyl acetate (WE) and Gelman Solvent Saturation Pads paper with ether (GE). Our results showed that the solvent developing times (n = 55) and Rf values for TP, WE and GE were 130.4 +/- 9.0 s/0.5-1.0, 205.9 +/- 13.0 s/0.2-1.0 and 90.2 +/- 7.5 s/0.8-1.0, respectively. For RCP values ranging from 45.0 to 94.6% (n = 61), both WE and GE closely correlated with TP (r = 0.97 and 0.96). However, in the intermediate RCP range (i.e. 75-85%, n = 25), the false RCP acceptance rate (i.e. RCP > or = 80%) was 40% (10/25) for the WE method versus 4% (1/25) for the GE method. The GE method has the most clear separation of lipophilic 99Tcm-exametazime from other radiochemical impurities and offers the quickest RCP analysis for 99Tcm-exametazime with relatively accurate results.