Determination of nanomolar levels of perchlorate in water by ESI-FAIMS-MS

Electrospray ionisation (ESI) was used to generate gas-phase anions that we re subsequently separated by high-field asymmetric waveform ion mobility sp ectrometry (FAIMS) and detected by quadrupole mass spectrometry (MS). ESI-F AIMS-MS provided selective and sensitive determination of perchlorate at lo w nanomolar levels, relatively free from the interferences commonly observe d 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 mu M perchlorate in a 10 mu M sulfate solution yielded a signal-to-bac kground ratio (S/B) improvement of over four orders of magnitude (at m/z -9 9) compared with ESI-MS. The detection limit for perchlorate (in 9:1 methan ol-water with 0.2 mM ammonium acetate and 10 mu M sulfate) was 1 nM (approx imate to 0.1 ppb).