Hubert Byliński, Jacek Gębicki, Tomasz Dymerski, and Jacek Namieśnik of the Faculty of Chemistry at the Gdańsk University of Technology in Poland have recently published a very insightful review of direct mass spectrometry (MS) techniques. Their review focuses on four of the more significant direct MS techniques, including Selected Ion Flow Tube Mass Spectrometry (SIFT-MS).
Direct MS has arisen because of a desire for reduced sample preparation and faster analysis than is provided by traditional techniques for analysis of organics, which are usually based on chromatography. The authors note in their abstract:
“One of the major sources of error that occur during chemical analysis utilizing the more conventional and established analytical techniques is the possibility of losing part of the analytes during the sample preparation stage. Unfortunately, this sample preparation stage is required to improve analytical sensitivity and precision. Direct techniques have helped to shorten or even bypass the sample preparation stage; and in this review, we comment of some of the new direct techniques that are mass-spectrometry based.”
This is indeed true of SIFT-MS! But SIFT-MS adds several benefits that no other direct MS technique does:
- Ultra-soft ionization.
“The SIFT-MS technique is closely related to the PTR-MS technique, but SIFT-MS provides several advantages. In SIFT-MS… the ionization in the flow tube is softer (in PTR-MS – drift tube and in SIFT-MS –flow tube). In the drift tube, there is much more fragmentation of analyte ions for the same compounds than in the flow tube, and in consequence, interpretation of the mass spectra can be more difficult. This effect can be related to higher collision energies in the drift tube (0.2 eV) than the thermal collision energies (0.038 eV) in the flow tube (Blake et al., 2009)…” (p. 347).
- The ability to instantly switch the species used for chemical ionization (the “reagent” or “precursor” ion).
“Furthermore, the switching between reagent ions in SIFT-MS is rapid as opposed to [proton transfer reaction switchable reagent ion mass spectrometry (PTR-SRI-MS)]…” (p. 347).
In practice, real-time switching means that:
“As opposed to the other design solutions using mass spectrometry, the SIFT-MS technique makes it possible to identify and distinguish between the chemical compounds with identical nominal mass but with a different arrangement of individual functional groups related to each other, such as acetone and propanol. It is possible that during one analysis several reaction ions can react with isobaric compounds, the result of which is completely different final products that are obtained from them, which reach the mass spectrometer analyzer…” (p. 347).
- Detection of a wider range of compounds.
“The SIFT-MS technique is more convenient than PTR-MS with hydronium ions as precursor ions in analysis of some compounds, such as formaldehyde or hydrogen cyanide, that have proton affinities close to that of water. In PTR-MS, where the effective temperature is much higher than in SIFT-MS (the order of 1000 K), the reactions between the protonated analyte and water in the sample take place at a much higher rate. It complicates the measurement of these compounds. In SIFT-MS, the compounds such as formaldehyde or hydrogen cyanide can be easily measured at room temperature during proton transfer reaction in the flow tube (Prince et al., 2010).” (p. 347).
Combined, these benefits make SIFT-MS unique among direct air analysis techniques, as Byliński et al. note in their summary (p. 353):
“Examination of the influence of the matrix on the final result of analysis is also an important element of the analytical procedure. In the case of the techniques described above, it is possible to control the relevant parameters to minimize the contributions from other compounds that may be present. The introduced modifications do not influence the possibility of determination of analytes at a trace level nor lengthen the time of sample preparation. These factors are in MALDI – MS, the matrix composition and in SIFT – MS, it is the selection of the precursor ion.”
SIFT-MS is a unique solution for gas and headspace analysis! For more information on SIFT-MS, view our introductory webinar, download our technology overview brochure, browse our website or contact us at firstname.lastname@example.org.
Read the full article (Hubert Byliński, Jacek Gębicki, Tomasz Dymerski & Jacek Namieśnik (2017) “Direct Analysis of Samples of Various Origin and Composition Using Specific Types of Mass Spectrometry”, Critical Reviews in Analytical Chemistry, 47:4, 340-358, DOI: 10.1080/10408347.2017.1298986).