移動度の電界強度依存性を利用した大気クラスターイオンの分離

抄録

Microchip-based high field asymmetric waveform ion mobility spectrometry (FAIMS) was used for the separation of the cluster ions generated by a corona ionizer in laboratory air. The hydrated cluster ions such as NO₃^-(H₂O)_n, NO₃^-HNO₃(H₂O)_n, and HCO₃^-HNO₃(H₂O)_n dominated the negative ion mass spectrum, while NH₄^＋(H₂O)_n along with H₃O^＋(H₂O)_n comprised the majority of the ion peaks in the positive ion mass spectrum. FAIMS spectra of these ions were measured using a FAIMS microchip coupled with an atmospheric pressure ionization mass spectrometer. FAIMS spectra of negative ions demonstrated that most of the negative ions tend to increase their mobilities with increasing the electric field strength and that the ions can be separated into up to six groups depending on the differences in ion mobility under a high and a low electric field. Separation of positive ions occurred at lower electric fields than that of negative ions. A single ion peak at low electric fields split into two peaks with increasing the field strength, but they merged to form a single peak again at a higher electric field. Another ion separation was observed to take place at even higher electric fields. This variation of positive ions in FAIMS spectra suggested that the mobilities of the separated ions initially decreased and subsequently increased with increasing the electric field.