Selected ion flow tube mass spectrometry (SIFT-MS) and proton transfer reaction mass spectrometry (PTR-MS) are techniques that offer real-time analysis for volatile organic compounds (VOCs) and both techniques use soft chemical ionization to analyze a wide range of VOCs.
SIFT-MS employs three positive reagent ions (H3O+, NO+ and O2+) and five negative ions (OH-, O-, O2-, NO2– and NO3-) all of which are produced in-situ by ionizing a mixture of ambient air and water. Application of three or more reagent ions gives SIFT-MS a significant advantage in the discrimination of isomeric compounds compared to PTR-MS.
In Syft Technologies SIFT-MS instruments, the reagent ions are rapidly mass selected in milliseconds and selectively react with trace VOCs in very well controlled thermal ion-molecule reactions in a carrier gas medium, allowing SIFT-MS to analyze whole air for VOCs at pptv levels in real time. The truly low levels fragmentation of the product ions enable the technique to be highly suitable for quantitation.
At inception PTR-MS used just protonated water ions (H3O+) as the reagent ion. Recently a “switchable” reagent ion (SRI-PTR-MS) has become available. However, the timescale for switching reagent ions is about ten seconds (offline) for PTR-MS hence making it impractical to monitor real-time changes with multiple reagent ions.
The reagent ions are not mass selected and are injected immediately into a drift tube where reactions occur with VOCs in the gas sample. Identification of the analyte is by means of the resulting product ion masses arising from uncontrolled reagent ion – analyte reactions hence producing inconsistent reaction products.
Syft Technologies’ SIFT-MS instruments provide very clear technical and operational advantages compared to the various commercial forms of PTR-MS. Significant advantages include but are not limited to:
- Rapid switching of reagent ions, allowing multiple reagent ions to be used in a single scan, saving time and sample, and allowing instantaneous results
- True soft ionization with lower energy and less fragmentation, meaning less spectral confusion and more precise compound identification and quantitation.
Want to learn more? Download the Technical Comparison of SIFT-MS and PTR-MS (white paper) or check our brochures