The most commonly used mass spectrometers in Earth and planetary sciences are magnetic sector and quadrupole spectrometers. These instruments operate by spatially separating ions according to their trajectories before detection. Other types of mass spectrometers utilize ion traps, where analysis is based either on the current induced by the ion trajectory (e.g., Orbitrap) or on the selective ejection of ions followed by their detection. One such ion-trap-based mass spectrometer is the Quadrupole Ion Trap Mass Spectrometer (QITMS). An example of a space-deployable QITMS for analyzing noble gases in atmospheres was developed by JPL (Avice et al., 2019). This instrument operates by applying a high RF voltage at a few MHz to a central electrode, trapping ions along trajectories that depend on their mass-to-charge ratio. Increasing the voltage destabilizes these trajectories, causing ions to be ejected and subsequently detected.
Another type of ion-trap-based mass spectrometer was recently developed by Ermakov and Hinch (2010). This instrument features a different design and operating principle, although the underlying philosophy remains the same. Ions are generated by electron emission from a filament, similar to any electron impact ion source. These ions are then trapped in an ion trap composed of two cages (entry and exit) separated by a transition plate that forms a potential well (-1000V). An RF voltage is also applied to this plate at a frequency of a few hundred thousand Hertz, but with a low amplitude (0.5V). By reducing the frequency, ions are ejected based on their mass-to-charge ratio (Ermakov and Hinch, 2010). This type of instrument is known as an “Autoresonant Ion Trap Mass Spectrometer.” This type of ion-trap-based mass spectrometer is compact in size. The picture shows the disassembled MS1 sited at ISTO. When mounted in a chamber, it measures 15 cm in length (compared to 30–40 cm for a quadrupole and over 200 cm for a magnetic sector spectrometer) and approximately 7 cm in diameter. Its weight is only a few hundred grams, depending on the type of chamber in which it is housed. Its electronics are also small and lightweight. Currently, its power consumption is around 24 W.
The primary advantage of ion-trap-based mass spectrometers lies in the speed of their mass scans, as only the RF frequency needs to be adjusted to eject ions from the trap. A scan from mass 0 to 145, for instance, takes just 80 ms. The collection system is also fast, even in ion-counting mode, which we aim to develop (a few microseconds per pulse). This rapid scanning capability allows for a very large number of analyses, minimizing the effect of ion consumption in the mass spectrometer—an issue faced by magnetic sector and quadrupole spectrometers, which have much slower scanning speeds. Thousands of scans can be performed in just a few minutes, something that is not feasible with other instruments.