SIFT-MS (Selected Ion Flow Tube – Mass Spectrometry) is an ultra-fast analytical tool for “smaller” molecules, typically up till MW 250, the system may however be used up till a MW 400. The system is based on a quadrupole analyser, and has a unit-mass resolution. The method has an extended selectivity, as it is possible to ionize with up till 3 different positive, or 5 negative ions, giving a soft ionization of the reactants. This gives an increased selectivity on molecules with the same MW, and therefore gives a possibility for the analysis of mixtures without GC or LC as a preceding separation method.
The possibility to analyse the “really small and polar molecules” is also an area where GC and LC have their limitations. Formic-/acetic acid and form-/acetaldehyde are analysed straight away down to 1ppb in most matrices. The system is available in two different set-up’s:
On-line use: Here a gas phase system is measured continuously. This set-up is therefore recommended for the monitoring of processes, indoor-air (the system is probably a dream for generating air-exchange data), in general, surveillance of processes where the concentration/development of target(s) has an impact on the process-in question.
Off-line use: This is a discontinuous measurement, where the samples are placed in vials. In this set-up the system is integrated with a GERSTEL autosampler/robot. The analysis time is typically around 60 -120 seconds between each headspace injection and the system is therefore well suited for a large number of analyses/24h. This may be microbiological screening or batch production control.
On its way!: The system has recently been developed in connection with a thermal desorber, and may therefore be used for the analysis of 3.5” TD tubes. We have not seen the system yet, but the sensitivity is probably down to low ppt, maybe high ppq. The analysis time will probably be around 5-10 minutes.
The system is built over a quadrupole mass spectrometer, but differs from an ordinary (GC-)MS system by not using EI but components from the surrounding air: : H2O, O2, NO, NO2 and NO3, which are ionized to form up till 8 precursor ions: H3O+, OH–, 02+, O–, O2–, NO+, NO2– and NO3–. The system may therefore easily analyse components in humid air, without bias.
These are selected for passage, one at a time, through the first quadrupole, and ionize the reactants which are added in a flow tube. Because of the soft ionization, only little fragmentation is seen, but the reactants ionize differently based of the choice of the precursor ion, this gives good selectivity also on more complicated matrices.
The ionized reactants are now analysed in the “Analyser” quadrupole, see also the video below. The system may be run in either continuous “Scan” mode, or with somewhat better sensitivity in “SIM” mode. As in ordinary GC/MS, the Scan gives the possibility to detect unknowns, whereas the SIM is mostly used for target analysis.
Contact: Jens Glastrup
Goto: SIFT-MS homepage
SYFT has released a number of brochures on the system:
General overview of the technology.