Trace analysis of impurities in 3′-azido-3′-deoxythymidine by reversed-phase high-performance liquid chromatography and thermospray mass spectrometry

Abstract An analytical method has been developed for the detection of trace amounts of impurities in 3′-azido-3′-deoxythymidine referred to herein as AZT (Zidovudine). A sample extract was preconcentrated by normal-phase high-performance liquid chromatography (HPLC) with subsequent on-line reversed-phase HPLC-thermospray mass spectrometry (TSP-MS). During the sample extraction and concentration step, carried out by semipreparative normal-phase chromatography, the preliminary separation of the impurities from the AZT takes place. The organic solvent (dichloroethane-acetonitrile, 40:60) is evaporated from the collected fractions and the compounds are redissolved in a smaller volume of the reversed-phase mobile phases for a further degree of concentration. The collected fractions are then subjected to reversed-phase HPLC-TSP-MS. The influence of acetonitrile concentration and pH on the reversed-phase separation together with the sensitivity of the TSP-MS detection have been examined to maximise detection levels. The 3′-azido-3′-deoxy-5′-O-tritylthymidine, triphenyl methanol and 3′-chloro-3′-deoxythymidine, which are route-indicative impurities formed during the synthesis can be detected in the 50–100 ppb (w/w) range.