Comparison of heterogeneous and homogeneous radioactivity flow detectors for simultaneous profiling and LC-MS/MS characterization of metabolites.

Methods for simultaneous liquid chromatography-radioactivity monitor (LC-RAM) metabolite profiling and LC-tandem mass spectrometry (MS/MS) characterization of metabolites are described. Profiling and characterization of metabolites from three drug candidates from different therapeutic areas were compared using in-line heterogeneous LC-RAM-MS/MS and homogeneous LC-RAM-MS/MS methods. Although comparison shows that simultaneous metabolite profiling and characterization can be achieved using either heterogeneous or homogeneous-LC-RAM-MS/MS systems, a homogeneous system has the advantage in the following aspects, (1) sensitivity; (2) ease of method transfer; (3) less peak broadening problems due to the drug or metabolites adhering to the RAM cell; (4) accuracy in quantitation of the metabolites; and (5) the ability to load larger volumes of unprocessed biological fluids. Furthermore, the study shows that some of the possible metabolites that do not ionize well with electrospray ionization (ESI) and eluded detection by heterogeneous-LC-RAM detection could be very easily detected and characterized using a homogeneous-LC-RAM-MS/MS system.