Thermo Scientific - What is FAIMS?

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What is FAIMS?


The patented FAIMS (high-Field Asymmetric waveform Ion Mobility Spectrometry) technology separates gas-phase ions at atmospheric pressure. Desolvated ions enter the annular region between two concentric cylindrical FAIMS electrodes and are transported toward the mass spectrometer entrance via a flow of clean, dry gas. Within the gas filled region of the electrodes, the ions oscillate as a result of a waveform causing alternating high and low electric fields. The waveform is asymmetric; the high field is applied for one time unit followed by an opposite-polarity low field component applied for twice as long. Separation of ions during the two opposite polarity phases of the waveform is caused by behavior differences of the ions under the high- and low-field conditions.
Over time, ions travel toward one or the other electrode. A low dc voltage compensates for this migration resulting in a select ion subset being transmitted into the MS. The magnitude of the so-called “compensation” voltage (CV) is compound dependent. Ions requiring a different CV for transmission are removed from the ion beam, thus selectivity is achieved. The CV may be set to a constant value or stepped during an LC-MS run to coincide with the elution of specific analytes. High analyte transmission efficiency is achieved with this increase in selectivity by means of a unique ion focusing mechanism arising from the cylindrical geometry of the FAIMS electrodes.