Abstract

Electrospray ionisation (ESI) was used to generate gas-phase anions that were subsequently separated by high-field asymmetric waveform ion mobility spectrometry (FAIMS) and detected by quadrupole mass spectrometry (MS). ESI-FAIMS-MS provided selective and sensitive determination of perchlorate at low nanomolar levels, relatively free from the interferences commonly observed for this analysis using conventional ESI-MS. In particular, the gas-phase separation of ions in FAIMS eliminated isobaric overlaps of bisulfate and dihydrogen phosphate with perchlorate. Using the FAIMS interface, analysis of 1 µM perchlorate in a 10 µM sulfate solution yielded a signal-to-background ratio (S/B) improvement of over four orders of magnitude (at m/z −99) compared with ESI-MS. The detection limit for perchlorate (in 9∶1 methanol–water with 0.2 mM ammonium acetate and 10 µM sulfate) was 1 nM (≈0.1 ppb).