Analyzing Volatile Organic Compounds (VOCs) In the Environment

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The analysis of volatile organic compounds (VOCs) is one of the most important topics under discussion at Pittcon 2017 in Chicago. The accurate measurement of VOCs enters numerous scientific arenas from the detection of VOCs as biological markers for cancer cells (health monitoring chemical fingerprint) [1] to monitoring the environment for levels of VOCs deemed harmful to human health [2, 3, 4].

The identification and quantification of both commercial (paints, coatings and fossil fuels) and naturally occurring VOCs has become an essential part of analytical chemistry. Volatile organic compounds typically occur at low levels and are many and varied and so research in this field requires detection and identification at low level requiring lower and lower limits of detection (LOD) or even ‘concentration’ (e.g., headspace analysis) and identification [5].

Traditionally the most useful methods have involved solid phase microextraction e.g., Tenax tubes and sensitive techniques such as GC-MS to resolve and quantify VOC mixtures [6] but there are now more sensitive techniques that can provide real-time sensing of VOC levels by direct injection mass spectrometry (DIMS) [7]. Some of these techniques [7] include MS-e-noses, atmospheric-pressure chemical ionization (APCI), proton-transfer-reaction mass spectrometry (PTR-MS), and selected ion-flow-tube mass spectrometry (SIFT-MS). All of these instrument configurations will be on display with various expert vendors during Pittcon 2017.

Direct Injection

Direct injection MS techniques are regularly used for rapid detection and accurate quantification of VOCs [7] and proton transfer reaction mass spectrometry (PTR-MS) [8] is one of the methods used regularly for the on-line analysis of biogenic and anthropogenic VOCs. State-of-the-art PTR-TOFMS instruments based on time-of-flight mass spectrometry such as the latest offering from Ionicon (Pittcon 2017) for ultra-trace VOC analysis have achieved detection limits of 20 parts per trillion after 100 ms and 750 parts per quintillion after just 1 min [9].

This type of system is ideal for the analysis of volatile organic compounds that might be obtained in a clinical environment, for example, the analysis of VOC cancer biomarkers from human breath samples. PTR-MS is a soft ionisation method that uses H3O+ ions to handover protons to all compounds that have a greater proton affinity than water. The nitrogen and oxygen in air are not ionised by the hydronium beam, but the majority of VOCs are ionised by H3O+ with little or no fragmentation.

Other molecules such as hydrogen sulphide (H2S), hydrogen cyanide (HCN) and ammonia (NH3) are also detectable by the H3O+ PTR-MS technique. The ionisation occurs in a low pressure reactor (0.1 to 2mbar) in dilute conditions to avoid any competition for charge between different analyte molecules, as could be possible with API sources.

Miniaturization and Portable Instruments

With the measurement of VOCs in the environment there has been a demand for miniature/portable mass spectrometry (MS) systems for in situ analysis. Miniature MS is now an attractive reality and the challenge to overcome the size and weight limitations of conventional MS has been realized. MS instruments are being condensed and improved to allow portability and accessibility, and some are even adapted for handheld operation.

Portability in MS is also a sign that systems are now amenable to ‘non-experts’ such as firefighters, police officers and environmental inspectors. MS miniaturization technology will be discussed at Pittcon 2017 in Chicago. Sessions will be provided on the subjects of ion traps and there will be a symposium on the ‘Miniaturization of MS’.

Various companies will provide presentations and demonstrate their mass spectrometer products across a range of applications. The Miniature Mass Spectrometry symposium will include a presentation on the Portable Digital Linear Ion Trap Mass Spectrometer from the Guangzhou Hexin Instrument Co., Ltd. This portable instrument has a foot print of only 45.5cm x 42.1cm x 22.1cm, a sensitivity of 5ppb @ 30 seconds sampling time (toluene), a scanning rate of 10000amu/sec and weighs less than 25 kg.

Environmental Sampling

For environmental detection in oil and gas installations or city centers handheld portability for MS systems is the best solution. In these cases the total VOC concentration is the important figure and a photo ionization detector is the ideal solution. The VOC-TRAQ® II from MOCON® Inc. – Baseline (exhibitor at Pittcon 2017) is a portable, hand-held, photoionization detector which is designed to evaluate total volatile organic compounds (TVOC). This highly compact instrument is ideal for air quality consultants or safety engineers, has no moving parts and with a rapid response time operates using just the simplicity of diffusion.

The analysis of air samples for VOC content over a set collection time has now been made easier with the availability of reliable automated detection systems. Extrel (exhibitor at Pittcon 2017) provide the MAX300-AIR Environmental Mass Spectrometer, which is custom designed for environmental VOC analysis. This instrument is an industrial gas analyzer that uses quadrupole mass spectrometry for the rapid detection and quantitation of a wide variety of VOC based industrial contaminants. A single analyzer can measure unlimited compounds and be automated to monitor more than 160 sample points across a manufacturing area.  Benzenes, esters, alcohols, ketones, alkanes, chloroalkanes and alkenes are the major emission components and the most frequently monitored VOCs are benzenes [10].

Conclusion

VOCs can be harmful to health and although the general consensus is that industries such as oil and gas, vehicle manufacture and furniture manufacture are the most prolific producers the highest health risk from VOCs is in the home and office. Instrumentation is now achieving a level of sophistication where VOC levels can be monitored in the workplace, on-site or even in the home to protect human health. The applications for VOC detection are many and varied and with the growing complexity of the range of VOCs that have to be monitored, organizations have to keep up with the most recent developments in analysis equipment. Miniature MS is set to be a definite advantage  VOC analysis and the Pittcon symposium is an ideal place to learn of recent developments.

References

  1. Kamila Schmidt and Ian Podmore, Current Challenges in Volatile Organic Compounds Analysis as Potential Biomarkers of Cancer, Journal of Biomarkers, Volume 2015 (2015), Article ID 981458, 16 pages, http://dx.doi.org/10.1155/2015/981458
  2. Russell, et al., Science, July 28, 1995, 269: 491-495;
  3. Bergin,et al., Environmental Science and Technology, December 1995, 29:3028-3037.
  4. Barro, R.; et al. (2009). "Analysis of industrial contaminants in indoor air: Part 1. Volatile organic compounds, carbonyl compounds, polycyclic aromatic hydrocarbons and polychlorinated biphenyls". Journal of Chromatography A. 1216 (3): 540–566.
  5. Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)”, U.S. Environmental Protection Agency, Office of Solid Waste, SW-846 Method 8260B, revision 2, December 1996.
  6. http://cdn.intechopen.com/pdfs/22746.pdf
  7. Biasioli, Franco; Yeretzian, Chahan; Märk, Tilmann D.; Dewulf, Jeroen; Van Langenhove, Herman (2011). "Direct-injection mass spectrometry adds the time dimension to (B)VOC analysis". Trends in Analytical Chemistry. 30 (7): 1003–1017.
  8. Ellis, Andrew M.; Mayhew, Christopher A. (2014). Proton Transfer Reaction Mass Spectrometry - Principles and Applications. Chichester, West Sussex, UK: John Wiley & Sons Ltd. ISBN 978-1-405-17668-2.
  9. Sulzer, Philipp; Hartungen, Eugen; Hanel, Gernot; Feil, Stefan; Winkler, Klaus; Mutschlechner, Paul; Haidacher, Stefan; Schottkowsky, Ralf; Gunsch, Daniel; Seehauser, Hans; Striednig, Marcus; Jürschik, Simone; Breiev, Kostiantyn; Lanza, Matteo; Herbig, Jens; Märk, Lukas; Märk, Tilmann D.; Jordan, Alfons (2014). "A Proton Transfer Reaction-Quadrupole inferface Time-Of-Flight Mass Spectrometer (PTR-QiTOF): High speed due to extreme sensitivity". International Journal of Mass Spectrometry. 368: 1–5.
  10. Wang, H., Nie, L., Li, J. et al. Chin. Sci. Bull. (2013) 58: 724. doi:10.1007/s11434-012-5345-2

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