Evaluation of high-field asymmetric waveform ion mobility spectrometry coupled to nanoelectrospray ionization for bioanalysis in drug discovery

The potential of high-field asymmetric waveform ion mobility spectrometry (FAIMS) coupled to nanoelectrospray ionization (nanoESI) as a method to improve sample throughput for bioanalysis in a discovery pharmaceutical setting was explored in this work. The ability of FAIMS to separate gas-phase ions in the millisecond timescale was exploited to eliminate the need for liquid chromatography. Samples were introduced into the FAIMS electrodes/mass spectrometer using offline nanoESI at 20 nL/min and 1.5 kV. Signals were averaged for 30 s after which the next sample could be analyzed. The separation of simple mixtures, e.g., the removal of metabolite and endogenous interferences from parent drug, was demonstrated. Moreover, the application of nanoESI attenuated the ion suppression effects that normally plague conventional electrospray. On average, approximately two-thirds of the neat sample signal intensity was preserved in extracted plasma samples. Standard curves were prepared for several compounds and linearity was obtained over approximately two to three orders of magnitude. This methodology was further tested with the analysis of plasma samples from a mouse pharmacokinetic study. Concentration values determined using nanoESI-FAIMS were comparable to those determined using conventional LC/MS as demonstrated by percent differences of less than 30%. This work demonstrated the proof of concept that the combination of FAIMS and nanospray ionization can be a potentially useful tool to improve the throughput of discovery bioanalysis.