Recent developments and applications of selected ion flow tube mass spectrometry (SIFT‐MS)

Abstract

Selected ion flow tube mass spectrometry (SIFT‐MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts‐per‐trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real‐time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT‐MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound (VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT‐MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT‐MS are mentioned.

Robust Automated SIFT-MS Quantitation of Volatile Compounds in Air Using a Multicomponent Gas Standard

“…The reaction mechanisms of the positively charged reagent ions have been reviewed in detail previously. , More recently, some discussion of the mechanisms of the negatively charged ions has been added, together with preliminary observations on the impacts of nitrogen carrier gas on ions of both polarities. , It is unnecessary to cover the mechanistic details again here. The salient point, however, is that SIFT-MS reagent ions provide multiple reaction mechanisms to the user, which enable real-time, simultaneous analysis of chemically diverse volatile compounds (see, e.g., the fumigant application), and selection of the most sensitive and specific product ions for the sample matrix. The relevance of a mechanism to a given compound depends on the specific gas-phase ionization energetics, and these generally follow trends for a given functional group.…”

“…8,13 However, while such methods are now widely adopted by industry, they are substantially different from the previously published methods lacking a gas standard. 14,15 This article, therefore, serves to fill an important need not covered in recent review articles on the ion−molecule chemistry 8 and applications 9 of SIFT-MS. It does this in two main ways.…”

Increasing the Robustness of SIFT-MS Volatilome Fingerprinting by Introducing Notional Analyte Concentrations

“…Selected ion flow tube mass spectrometry (SIFT-MS) is a relatively underexploited analytical technique for real-time analysis of volatile organic compounds (VOCs) and inorganic gases and has been extensively reviewed elsewhere. − …”

How to Use Ion-Molecule Reaction Data Previously Obtained in Helium at 300 K in the New Generation of Selected Ion Flow Tube Mass Spectrometry Instruments Operating in Nitrogen at 393 K

“…Selected ion flow tube-mass spectrometry (SIFT-MS) is a soft chemical ionization technique increasingly used globally to directly analyze volatile organic compounds (VOCs) within gaseous media. , SIFT-MS has become a particularly popular technique in the analysis of human breath in clinical settings; , the monitoring of the environment (i.e., atmospheric chemistry); − headspace analysis of samples (such as foods and cosmetics); , the analysis of contaminants within hydrogen (as a fuel); as well as airborne molecular contaminants in semiconductor manufacturing . A common theme in this diverse scope of applications of SIFT-MS is the attempt at immediate and absolute quantification of targeted VOCs.…”

“…It is, however, important to note that conditions in various instruments used over the last 35 years have not always been identical. Many original studies of the ion chemistry of H 3 O + , NO + , and O 2 +• reagent ions were completed on laboratory SIFT instruments with flow tubes 40 to 100 cm long, operating with He at a pressure of 0.5 Torr at a temperature of 300 K. Later, smaller instruments called Mk 1, Mk 2, Profile 3 , Voice100, and Voice200infinity were developed and used for SIFT kinetics studies, initially in He, at pressures ranging from 0.6 to 1 Torr and temperatures between 300 and 400 K. , Later, the N 2 carrier gas was introduced, which is now used almost exclusively at pressures of 0.4 to 0.5 Torr and temperatures from 390 to 400 K for practical analyses using the Voice200infinity. ,, …”