Development of a Continuously Stirred Tank Reactor for Quantitative Binding Determinations using Flow Injection Analysis Electrospray Ionization - Mass Spectrometry

Knowing the binding strength between a drug and its target is a key factor in determining the effectiveness of a drug. Electrospray ionization-mass spectrometry (ESI- MS), a highly sensitive analytical tool, can be used to study drug-target binding. Coupled with flow injection analysis (FIA), ESI-MS binding determinations can be performed faster and more precisely than traditional techniques. Yet, the ESI process can perturb solution binding and introduce error into the measurement. Consequently, a continuously stirred tank reactor (CSTR) arrangement was developed to address this limitation. As a FIA device, the CSTR produces a consistent exponential decay of analyte concentration from a single sample injection. Several experiments are needed to characterize the CSTR before it can be used for ESI-MS binding determinations. First, algorithms describing the analyte independent nature of exponential decay under constant flow rate conditions were validated in a single phase device. Next, a CSTR containing a dispersed solid phase was constructed to study the analyte dependence of decay times.  Analytes that strongly interact with the second phase will be retarded from leaving the device; the result is a net increase in the effective volume experienced by the analyte. With these results in place, a system can be devised to measure the interactions between various species in solution; binding information will be contained in the shape of the decay curve, rather than the magnitude of the mass spectral response for the complex.  As such CSTR FIA-ESI-MS has significant potential to aid the drug discovery process.