As the application of LC/MS entered ever more challenging areas, the demand for an added dimension of differentiation was needed, which helped to give rise to ion mobility–enabled MS. Several major vendors now offer the technology.

Ion mobility is a technique that utilizes an applied electric field to separate molecular ions based on their mobility through a buffer gas that can either be at atmospheric pressure or significantly lower. An individual ion’s mobility is based on its size and shape, as well as its mass and charge. This is in contrast to MS, which separates ions based only on their mass-to-charge ratio. Ion mobility provides a complementary dimension of separation that is useful with isobaric species.

Stand-alone ion mobility spectrometers (IMS) are used for explosives and narcotics detection and defense applications, but the combination of the technology with MS is a more recent development. While the majority of LC/MS applications do not require the technology, an increasing number of applications, mostly in bioanalysis, can greatly benefit by the use of ion mobility to separate more complex samples that are more likely to have hard-to-resolve compounds.

There are two major ways in which ion mobility is integrated with MS systems. The first to be developed, and the far simpler method, is to use it as an ion-filtering device at the inlet to the MS. Ion mobility–filtering technology, referred to as Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) by some and differential ion mobility spectroscopy by others, is available as an aftermarket product or an integrated option on new LC/MS systems. Such technology has been applied to ion traps, triple quadrupoles and Q-TOF MS systems. A more advanced usage of ion mobility technology is to integrate it in between mass analyzers, where it is used more as an additional dimension of separation, rather than simply a filter. This requires higher-speed systems and is much more difficult to manage. This more advanced usage has thus far only been designed into high-end Q-TOF systems.

Although the first development of ion mobility technology for coupling to MS began in the 1980s, the first commercial product was not released until 2001 when Ionalytics introduced an aftermarket FAIMS module (see IBO 5/15/03). Although the company pursued agreements with all major LC/MS vendors, Thermo Fisher Scientific acquired Ionalytics in 2005 (see IBO 8/15/05). In 2006, Waters began an overhaul of its Q-TOF LC/MS product line with the introduction of the SYNAPT line (see IBO 6/15/06), which incorporated Triwave ion mobility technology after the quadrupole mass analyzer. At ASMS, AB SCIEX introduced SelexION technology (see page 8).

The market for LC/MS systems with ion mobility capabilities is now close to $100 million annually and should see very strong double-digit growth in the near term. New offerings should drive the adoption rate.

IMS-MS at a Glance:

Leading Suppliers

• Thermo Fisher Scientific

• Waters

• AB SCIEX

Largest Markets

• Pharmaceutical

• Academia

Instrument Cost

• $400,000–$800,000 (full systems); $75,000–$100,000 (upgrades/aftermarket)