Three-Dimensional Quadrupole Ion Traps in PTR-MS

The first description of an ion trap in a PTR-MS instrument was published in 2003. To date there are three distinct research groups that have constructed PTR ion trap mass spectrometers (PTR-IT-MS) [51-53]. Some of the driving forces for replacing a linear quadrupole mass filter with a 3D quadrupole trap have been described above, including the convenience for ion-selective CID and the small size of the trap. Another motivation 

Contrast this with a linear quadrupole, which at any instant in time transmits ions with only a single m/z and rejects all others. The duty cycle achieved will depend on the chosen mass scan range and the scan speed but will at best be just a few percent. Consequently, the ion trap is capable of a much higher duty cycle than a linear quadrupole (assuming the latter is operated in the mass scanning mode). However, this need not necessarily translate into a higher detection sensitivity since other factors will also affect this, such as ion transmission efficiency from the drift tube to the quadrupole trap. 

The best limit of detection that has so far been achieved with PTR-IT-MS instruments based on a 3D ion trap is in the region of 50-100 pptv for specific VOCs such as toluene and benzene using 1 min of data accumulation [52] 

---