Radiochemical purity of D,L-hexamethylpropylene amine oxime and analysis of urine-excreted HMPAO decomposition species.

The radiochemical purity of hexamethylproxypropylene amine oxime (HMPAO) was determined in 16 preparations using the three-strip method. Immediately post-formulation, 90.3% +/- 4.0% (mean +/- SD) of the activity was associated with the primary lipophilic complex having an Rf of 0.45 +/- 0.11. We recorded a significantly higher content of sodium pertechnetate Tc 99m in methylethyl ketone (MEK) (21.1% +/- 8.5%) than in saline (5.0% +/- 3.7%; P less than 0.001). To clarify this finding, we ran sequential chromatograms (t = 0, 1, 2, 3 h) and found that the primary complex steadily disappeared, with a rate constant of 0.31 h-1. These results suggest that there is a decomposition of the primary complex during chromatography in MEK that might be responsible for the larger fraction of sodium pertechnetate Tc 99m in MEK. Eluate composition might influence the Rf of the lipophilic complex and the rate of its in vitro decomposition. In another experimental setting, we investigated 99mTc-HMPAO decomposition species in urine after application of a suspension of labelled leukocytes by performing sequential chromatographic analyses in 11 patients. At 1 h after application, urinary activity reflected the presence of a secondary complex (84.8% +/- 9.2%) and sodium pertechnetate Tc 99m (15.2% +/- 9.2%). The values after 3 h were markedly different (91.4% +/- 4.8% and 8.6% +/- 4.8%; P less than 0.001). Thus, urinary activity mostly consisted of a secondary complex, increasing with time.