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New integrated solution reliably measures air toxins

By Laura Provoost
Agilent GC Product Manager

Air pollution is an issue of major concern worldwide. Pollutants in the air can be encountered both indoor and out. These toxic particulates are found in everything from vehicle exhaust to cooking fires… forest fire smoke to volcanic eruption vapor, as well as volatiles and semivolatiles from industrial processes. The challenge for analysts is to gather uniform samples and execute multiple testing methods seamlessly on an ongoing basis.

To provide analysts with a robust solution – that enables autosampling, reduces gas and energy use, and simultaneously analyzes volatiles and semivolitiles – we combined the capabilities of the Agilent 7890B GC system and Agilent 5977A Series GC/MSD with the Markes UNITY thermal desorption (TD) system. The Markes UNITY TD captures organic pollutants prior to injection – and when combined with the Agilent 7890B GC and 5977A MSD, provides a complete system for air sampling, desorption, and testing. It is an integrated solution enabling consistent sampling that conforms to standard methods and routinely achieves lower detection limits. In this article, we will discuss two applications to demonstrate how well it works.

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Figure 1. Diurnal profile of selected hydrocarbons, showing distinct differences between traffic-free and traffic-heavy periods.

Unattended round-the-clock air analysis

Volatile hydrocarbons in urban air could contribute to the production of ground-level ozone, one of the main constituents of smog. These compounds of interest are generally referred to as ozone precursors. Vehicle emissions are thought to be the main source of ozone precursors, which range in volatility from acetylene (ethyne) to trimethylbenzene and include benzene, toluene, xylene and buta-1,3-diene. European [1] and US regulations [2] require round-the-clock monitoring of target species in all major urban centers to assess possible links between periods of high traffic density and high pollution levels. This continuous real-time monitoring also provides an insight into industry emissions and can be used to monitor weather effects such as wind direction, rainfall, and temperature inversion.

To evaluate the combined system’s unattended performance in the field, we analyzed air quality from a forested semi-rural area that has high volumes of traffic during the working week and very few cars on weekends. Figure 1 shows a diurnal profile of various compounds from 4:40PM on a Sunday through Monday evening.

The difference between the traffic-free and peak periods was distinct. Most of the hydrocarbons were at low levels during the traffic-free periods, with rapid increases during peak commuting hours. Importantly, the system ran unattended with no intervention required during the trial, while detection limits – even in this relatively clean environment – were also satisfactory.

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Figure 2. Chromatograms of air samples from office, laboratory, and outside were collected using “Universal” sorbent tubes and desorbed splitless.

EPA Method TO-17 for monitoring air toxins

We collected office, laboratory, and semi-rural outside air samples onto Markes ‘Universal’ sorbent tubes. The sample flow rate was 50 mL/min for 20 minutes, giving a total volume of 1 L in each case. We then analyzed each sample tube splitless using a full-scan MS method from 10 to 300 amu. The data are shown in Figure 2. Semivolatiles that were not seen in the laboratory or outside air samples were evident in the office sample, presumably outgassed from soft furnishings.

Trust our combined solution for consistently accurate air analysis.

Government and industry laboratory chromatographers who want reliable, accurate, and consistent air pollution testing of volatiles and semivolatiles can rely on the Agilent 5977/7890B Series GC/MSD and Markes Unity Series 2 TD integrated system. Take time now to learn more about the many benefits of Agilent’s air analysis solutions, and order your copy of our new Air Monitoring Poster (5991-2380EN).

Acknowledgment

We thank Markes International Ltd for use of the chromatograms and supporting text.

References

1. EC directives 96/62/EC (1996) and 2000/69/EC (2000). http://ec.europa.eu/environment/air/legis.htm
2. US Clean Air Act Amendments (1990). http://www.epa.gov/air/caa/

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