Frequently asked questions about ultraFAIMS

What is ultraFAIMS?

UltraFAIMS is a microscale chip-based field asymmetric ion mobility spectrometer designed for interfacing with mass spectrometers to provide extra separation of ions based on their differential mobility.

Can it be interfaced with any mass spectrometer?

The ultraFAIMS chip has a very small footprint (approx 2mm thick and 17mm in diameter) and can be floated to 6kV, which means it can be interfaced with most mass spectrometers. Our objective is to develop interfaces compatible with a wide range of mass spectrometers (see our products page for up to date information on available interfaces), and we also provide a development kit for users who would like to develop a bespoke interface.

Does it work with ionization sources other than electrospray?

Yes, any ionization source can be interfaced with the device provided it produces desolvated gas phase ions. Our stand-alone products use radiation sources, corona ionization and UV ionization, and ultraFAIMS has been interfaced with standard ESI, nanospray, DESI and extractive electrospray sources.

Do I have to remove the ultraFAIMS device when I don’t need extra separation?

Not necessarily. When the ultraFAIMS separation fields are disabled, the device transmits all ion species simultaneously and this makes it extremely quick to switch between FAIMS and non-FAIMS mode. Inevitably there will be some ion losses while the device is in place, so when sensitivity is critical you may wish to remove the device. This can be done in a few minutes without venting the mass spectrometer.

How does it work?

In a FAIMS device, ions pass between a pair of electrodes across which an alternating high/low electric field is applied. This electric field, known as the dispersion field (DF), makes the ions drift towards one or other electrode, with the drift velocity being a function of the field strength, the charge on the ion and the way the mobility of the ion changes between the high and low field portions of the cycle. The change in mobility is due to changes in the collision cross section of the ion resulting from structural rearrangements or clustering/declustering with neutral ions under the influence of the field. The net sideways drift means that most ions collide with the electrodes and are annihilated. However, ions can be selectively transmitted by superimposing a DC field, the compensation field (CF), in the opposite direction across the electrodes to cancel out the sideways drift – at different CF values, different species are transmitted. FAIMS devices can generally all operate in filtering mode, where the CF is held at a fixed value to transmit a subset of ions, or gradually stepped through a discrete range of values. Certain FAIMS devices, including ultraFAIMS, are also able to operate in scanning mode, where the CF is repeatedly swept through a range of values, producing a spectrum of ions separated by differential mobility.

How do I decide what settings to use?

In many cases you can use whatever LC, source and MS settings you normally use for the method you are running. To find the FAIMS parameters, the easiest way is to run a two-dimensional sweep – in which the CF is repeatedly swept over the full range, with the DF gradually being increased in steps. You can then review the data produced to determine what CF and DF values appear to give the best separation of the analytes you are interested in. You might then choose to cycle through a sequence of static CF/DF points, e.g. for targeted analysis, or to fix the DF and continue sweeping the CF through all or part of the full range for a more untargeted analysis.

Do I need additional gases or consumables?

The system does not require any additional gas flow to operate and the only consumable is the ultraFAIMS chip itself. Solvent modifiers or alternative gases can optionally be added to the carrier gas flow to enhance separation in some cases, but these are not essential.

Can modifiers be used to enhance separation with ultraFAIMS?

Yes, as mentioned above, the addition of solvent vapours to the carrier gas at the low percent concentration level does change the differential mobility behaviour of ions in the ultraFAIMS device, and this can provide a way of significantly enhancing separation – this is thought to be due to clustering/declustering of the analyte ions with the solvent molecules causing a change in differential mobility. Effective modifiers include methanol, butanol, acetone, acetonitrile, and isopropanol, although currently the behaviour of different modifiers is hard to predict a priori, so selection of a modifier tends to be an empirical process. Gases such as carbon dioxide, argon, helium or hydrogen can also be used as modifiers (typically at much higher concentrations than solvent vapours).

What peak capacity does it provide and how much does it affect transmission?

Without modifiers, the basic peak capacity of the device is around 10-15, and transmission compared to the non-FAIMS mode typically ranges from approximately 5-100%, though this is analyte specific. In many cases, the absolute transmission is not the key metric, but rather the increase in signal-to-background provided by the device – this is very application dependent but results so far have shown that increases of up to several orders of magnitude are possible.

How do you clean the chip and how long does it last?

The chip module can be removed from the interface for cleaning in a couple of minutes. It can then be submerged in suitable cleaning solvents and sonicated for a few minutes. The choice of solvent will depend on what analytes and solvents you have been running through the device. Once the chip has dried thoroughly, it can be replaced onto the interface. Chip lifetime is very dependent on usage and frequency of cleaning, but they typically last a few months before any performance degradation is seen. The chip module is a consumable part and replacements can be ordered from Owlstone.

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