WHAT is High-Field Asymmetric Waveform Ion Mobility Spectrometry?

FAIMS is a new technology capable of separation of gas-phase ions at atmospheric pressure (760 torr) and at room temperature. FAIMS can be operated over a wide range of pressures and has been tested above 1500 torr. FAIMS will operate at lower and higher temperatures.

Why is it called FAIMS?

In order for FAIMS to operate, several essential conditions must be met:

(1)Strong electric fields are required. FAIMS typically operates with fields of 10 000 volts/cm.

(2) A periodic electrical waveform is applied to conductive surfaces about 2 mm apart. The electrical waveform must be 'asymmetric', which means that there is a significant difference between the peak +ve voltage, and the peak -ve voltage during the applied waveform. Either of the +ve or the -ve may be higher voltage. For an example, see "How does FAIMS work?".

(3)The device is based on "ion mobility", which means that an electric field is used to drag the ions through a gas which is dense enough that the ions rapidly reach a terminal velocity. The terminal velocity is roughly proportional to the strength of the electric field. This proportionality changes at high electric field and makes the operation of FAIMS possible. Just as importantly, this proportionality is compound-dependent, permitting the separation of ions from each other.

If conditions (1), (2), and (3) are all met, then the device is capable of functioning as a High Field Asymmetric Waveform Ion Mobility Spectrometer.

Does FAIMS have unique properties?

FAIMS is a new atmospheric pressure ion separation technology

Existing ion mobility systems (some available commercially) have the capability of ion separation at atmospheric pressure. FAIMS is a new variation of ion mobility spectrometry. In FAIMS the ions are separated according to their properties while drifting in very high electric fields. Simply stated, each type of ion has an ion mobility which is a constant in low electric fields. At high fields the mobility of each ion deviates from its low-field value. The extent of that deviation is the key to ion separation in FAIMS. More to follow ...

FAIMS is the worlds first atmospheric pressure ion focusing device

Ion focusing means that the ion density increases, analogous to the light intensity increase due to a focusing lens. In other words, the ions are brought into closer and closer proximity to each other as time passes. The ion cloud is compressed, or focused, in volume. Two forces try to expand the ion cloud, ion-ion repulsion and diffusion. In FAIMS these two forces are overcome and the ions are forced together. The ion cloud increases in density (the number of ions per unit volume). No other means of compressing the ion cloud (at atmospheric pressure) exists. In a vacuum, devices such as quadrupoles and ion traps can do this, but these devices fail at higher pressure. FAIMS is the worlds first atmospheric pressure ion trap

Ion trapping is fairly simple. An ion trap mass spectrometer can isolate and hold ions without loss. Unfortunately those devices fail at higher pressure . Only FAIMS can collect and hold ions in a confined place (thus trapping them) at atmospheric pressure .

More details of High Field Asymmetric Waveform Ion Mobility Spectrometry in the next section: How does FAIMS work? HOW