Measuring trace volatile organic compounds (VOCs) in the Earth’s atmosphere can shed light on important processes, such as the formation of photochemical smog or the formation of aerosols. However, as VOCs typically occur at low levels in the atmosphere and can be reactive, measuring them has often required time-consuming sample preparation techniques that increase analytical uncertainty.
Measuring samples directly can overcome this problem. Selected ion flow tube mass spectrometry (SIFT-MS) directly analyzes and quantifies traces gases in real-time. A research team at the Max Planck Institute for Biogeochemistry in Germany recently set SIFT-MS the task of measuring trace VOCs, optimizing their methods to meet the challenges associated with atmospheric trace gas analysis.1
So, how did SIFT-MS perform? The research team found that SIFT-MS could effectively perform direct measurement of a mixture of trace VOCs. Though SIFT-MS has detection limits suitable for routine trace gas analyses in atmospheric samples as standard, the researchers were able to push these limits to sub-ppb levels, allowing for analysis of lower-than-ever concentrations. They also evaluated instrument stability over time, an important factor when collecting atmospheric data, especially over longer time periods. They found that the easy and rapid daily validation function offered by Syft Technologies SIFT-MS delivered good long-term stability and could be further improved by customizing the method.
The researchers then compared SIFT-MS to another technology that allows direct analysis of gases: proton transfer reaction mass spectrometry (PTR-MS). Whilst SIFT-MS had comparable dynamic range and sensitivity to PTR-MS, SIFT-MS outperformed PTR-MS in several key ways. Firstly, SIFT-MS was more robust to changes in humidity than PTR-MS. This is an important advantage when measuring atmospheric samples, which vary in water content. Secondly, SIFT-MS was identified as more useful than PTR-MS for analyzing mixtures, such as would be found in real samples. This is because the additional reagent ions and reactions offered by SIFT-MS provide extra information about compound structure and allow separation of certain isomeric compounds. Finally, the ease of use and lower cost of SIFT-MS were highlighted.
The take home message? SIFT-MS can meet the challenges of measuring VOC trace gases in atmospheric samples, whilst offering cost effectiveness, ease of use and cutting-edge performance.
- Lehnert, A.-S., Behrendt, T., Ruecker, A., Pohnert, G., and Trumbore, S. E.: SIFT-MS optimization for atmospheric trace gas measurements at varying humidity, Meas. Tech., 13, 3507–3520, 2020.
The full text of the article is available here: https://doi.org/10.5194/amt-13-3507-2020