High-field asymmetric-waveform ion mobility spectrometry (FAIMS or RF-DC ion mobility spectrometry) is an
ion mobility spectrometry
Ion mobility spectrometry (IMS) is an analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas. Though heavily employed for military or security purposes, such as detect ...
technique in which ions at
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibar ...
are separated by the application of a
high-voltage
High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant spe ...
asymmetric waveform at
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the uppe ...
(RF) combined with a static (
DC) waveform applied between two electrodes.
Depending on the ratio of the high-field and low-field mobility of the ion, it will migrate toward one or the other
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
. Only ions with specific mobility will pass through the device.
Application
One application of FAIMS is as an additional separation step between the liquid chromatography separation and mass spectrometric analysis in
Liquid chromatography–mass spectrometry
Liquid chromatography–mass spectrometry (LC–MS) is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography (or HPLC) with the mass analysis capabilities of mass spectrometry (MS). Coupled ...
(LC-MS) as used in
proteomic studies. It allows for online
fractionation
Fractionation is a separation process in which a certain quantity of a mixture (of gases, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in whic ...
of the
analyte
An analyte, component (in clinical chemistry), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The purest substances are referred to as analytes, such as 24 karat gold, NaCl, water, et ...
components to improve detection of
peptide
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...
s in complex samples. LC-MS uses the mass to charge ratio of peptide ions to analyse samples and the resulting spectra are compared to spectral reference libraries. FAIMS can be used to filter out "chemical noise", i.e. compounds whose spectra would interfere with the spectra of the desired compound, either by overlapping with the desired compound's spectra or adding additional peaks to the spectra. It can be used to filter out interfering ions and simultaneously select peptides with charge states that are optimal for analysis.
A further advantage of this technique is that it can be used to select for peptide ions that are of low abundance in the sample. Such low abundance ions are often not analysed because of the limitations of the duty cycles of the mass spectrometers. By selectively removing the more abundant ions FAIMS can assist in distinguishing between ions with similar mass to charge ratios and can prevent a more abundant ion from masking the presence of a less abundant ion.
Devices
Devices utilizing the principle of RF-DC ion-mobility spectrometry include handheld explosive trace detectors "MO-2M" and "Pilot-M".
See also
*
Ion mobility spectrometry
Ion mobility spectrometry (IMS) is an analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas. Though heavily employed for military or security purposes, such as detect ...
*
Electrical mobility
Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field that is pulling them. The separation of ions according to their mobility in gas phase is called io ...
References
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Mass spectrometry