Direct, rapid quantitative analyses of BVOCs using SIFT-MS and PTR-MS obviating sample collection

doi:10.1016/j.trac.2011.05.001

TrAC Trends in Analytical Chemistry

Volume 30, Issue 7, July–August 2011, Pages 945-959

https://doi.org/10.1016/j.trac.2011.05.001 Get rights and content

Abstract

The purpose of this short review is to describe the origins and the principles of operation of selected-ion flow-tube mass spectrometry (SIFT-MS) and proton-transfer-reaction mass spectrometry (PTR-MS), and their application to the analysis of biogenic volatile organic compounds (BVOCs) in ambient air, the humid air (headspace) above biological samples, and other samples. We briefly review the ion chemistry that underpins these analytical methods, which allows accurate analyses. We pay attention to the inherently uncomplicated sampling methodologies that allow on-line, real-time analyses, obviating sample collection into bags or onto traps, which can compromise samples.

Whilst these techniques have been applied successfully to the analysis of a wide variety of media, we give just a few examples of data, including for the analysis of BVOCs that are present in tropospheric air and those emitted by plants, in exhaled breath and in the headspace above cell and bacterial cultures (which assist clinical diagnosis and therapeutic monitoring), and the products of combustion. The very wide dynamic ranges of real-time analyses of BVOCs in air achieved by SIFT-MS and PTR-MS – from sub-ppbv to tens of ppmv – ensure that these analytical methods will be applied to many other media, especially when combined with gas-chromatography methods, as recently trialed.

Section snippets

Introduction and overview

As discussed in other contributions to this Special Issue, the standard approach to the analyses of biogenic volatile organic compounds (BVOCs) in air usually involves the collection of samples into vessels or onto traps, followed by extraction of the BVOCs and their separation by a GC column [1]. With proper use of standards and careful calibration, this approach provides reliable results, but currently cannot deliver absolute quantification in real time. Selected-ion flow-tube mass

Origins of SIFT-MS and PTR-MS

These techniques exploit fast flow-tube or drift-tube reactors combined with CI to analyze trace compounds in air samples in real time, avoiding sample collection and constant calibration, and can provide accurate quantification at the parts-per-billion by volume (ppbv) level and below. However, there are clear differences between SIFT-MS and PTR-MS, which are made clear in the next two sections. Both are developments of the SIFT technique that was created to study the reactions between ions

Ion chemistry underpinning SIFT-MS and PTR-MS

The essential aspect of both SIFT-MS and PTR-MS is the use of soft CI, which minimizes fragmentation of the characteristic product ions, reduces mass spectral overlaps and allows mixtures of compounds in air to be analyzed without using time-consuming separation techniques (as used in GC-MS), thus facilitating real-time analyses. The commonly adopted reagent ions are H₃O⁺, NO⁺ and $O_{2}^{+}$ (occasionally ${NH}_{4}^{+}$ has been used [32]), which are unreactive with the major components of air. So many studies

Sampling methodologies

The major contribution made by both SIFT-MS and PTR-MS is that they provide instruments by which the concentrations of trace gases in air, exhaled breath and headspace above liquids and cultures can be measured in real time, obviating sample collection into bags or onto traps. Thus, the sample and its analytes are not modified or disturbed, and, since many BVOCs are fragile molecules, this is obviously advantageous. Also, the analyses are immediately available, clearly valuable to the health

Illustrative examples of direct analyses of BVOCs

During the relatively short period of existence of SIFT-MS and PTR-MS, these analytical methods have been used for the analyses of many different media. These have been surveyed in recent review papers {SIFT-MS [2], [3]; PTR-MS [4]}. In this short review, we can give only a few examples to illustrate the value of these techniques for the analysis of BVOCs. SIFT-MS has played a leading role in the development of breath research, specifically for the on-line, real-time analysis of trace-gas

Summary remarks and future perspectives

The great value of SIFT-MS and PTR-MS for the analysis of BVOCs is their real-time facility, which avoids sample collection into bags or onto traps that can promote compound modification, and the instant quantification that can be confidently obtained without the need for regular instrument calibration. Also, the very wide analytical range is impressive; SIFT-MS covers concentrations ranging from percentage to ppbv; PTR-MS extends the available sensitivity to sub-ppbv levels and approaching

Acknowledgements and disclosure of conflict of interest

We wish to thank all colleagues who contributed to the work reported in the cited papers and also to Thomas Chippendale for assistance in obtaining SIFT-MS data. No external funding has been used in the preparation of this review. Both authors are Directors and shareholders of Trans Spectra Limited, UK.

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Direct, rapid quantitative analyses of BVOCs using SIFT-MS and PTR-MS obviating sample collection

Abstract

Section snippets

Introduction and overview

Origins of SIFT-MS and PTR-MS

Ion chemistry underpinning SIFT-MS and PTR-MS

Sampling methodologies

Illustrative examples of direct analyses of BVOCs

Summary remarks and future perspectives

Acknowledgements and disclosure of conflict of interest

Atmos. Environ.

Int. J. Mass Spectrom. Ion Processes

Adv. At. Mol. Phys.

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

J. Am. Soc. Mass Spectrom.

BMC Res. Notes

Ann. Occup. Hyg.

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

J. Environ. Monit.

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Kidney Int.

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Bioresour. Technol.

Int. J. Mass Spectrom. Ion Processes

Int. J. Mass Spectrom. Ion Processes

Atmos. Environ.

Int. J. Mass Spectrom. Ion Processes

Build. Environ.

Mass Spectrom. Rev.

Mass Spectrom. Rev.

Chem. Rev.

Mass Spectrom. Rev.

Analyst (Cambridge, UK)

Mass Spectrom. Rev.

Swarm techniques

SIFT applications in mass spectrometry

Med. Biol. Eng. Comput.

Rapid Commun. Mass Spectrom.

Chem. Soc. Rev.

J. Appl. Physiol.