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 analyzer 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 analyze the “really small and polar molecules” is also an area where GC and LC have their limitations. Formic-/acetic acid and form-/acetaldehyde are analyzed straight away down to 1ppb in most matrices.
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.
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.
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.
Theese are 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 analyze 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 analyzed in the “Analyzer” quadrupole.
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
Photo from our demolab in Skovlunde. With GERSTEL MPS on the top.
The system has recently been developed in conjunction with a GERSTEL thermal desorption system, and can therefore now also be used for the analysis of 3.5 ”TD tubes. The system enables really fast analysis, with typical run times between 3 – 7 minutes.
The TD tubes are fed by a GERSTEL Robotic autosampler, and therefore the system may also be used for (really fast) static headspace analysis. These possibilities extend the versatility of the SIFT.
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