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2,3,3,3-tetrafluoro-2-(trifluoromethyl) propanenitrile (C$$_4$$F$$_7$$N) is being researched as an alternative to sulfur hexafluoride (SF$$_6$$) for applications in gas-insulated switchgear. We independently assessed the effectiveness of gas chromatography-mass spectrometry (GC-MS) and a novel method of feedback-assisted multipass-cavity spontaneous Raman spectroscopy (SRS) for the trace quantification of impurities in C$$_4$$F$$_7$$N and its related byproducts. A total of fourteen gases were identified with estimated concentrations as low as 20 parts-per-million (ppm) for C$$_3$$F$$_6$$ using GC-MS and 7.4 ppm for CH$$_4$$ using SRS, and as high as 500 ppm for CF$$_4$$ using GC-MS and 1430 ppm for CO using SRS. While GC-MS is highly effective in selectively detecting and quantifying trace contaminants, it necessitates separate detectors for various gases, such as CH$$_4$$ and H$$_2$$. SRS succeeded in detecting CF$$_4$$ and C$$_2$$F$$_6$$ at concentrations of 465 and 100 ppm, respectively, and in placing an upper bound of several hundred ppm for other analytes. Crucially, SRS holds potential for portability---and thus for field applications---in gas-insulated switchgear equipment diagnostics.
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Raman scattering applied to human breath analysis
The chemical composition of exhaled human breath can be strongly correlated to medical conditions such as lung cancer or gastrointestinal diseases. To establish these correlations and, most importantly, to use them in diagnostics, chemical gas detection needs to be performed at trace concentrations, typically at parts-per-million (ppm) levels or below, for many compounds simultaneously. Traditional methods such as gas chromatography, a workhorse in scientific laboratories, is ill-suited for the fast, inexpensive point-of-care diagnostics that would be needed to build statistically-meaningful ensembles over large populations. With the increasing availability and decreasing cost of high power diode lasers and of uncooled CMOS cameras, spontaneous Raman spectroscopy (SRS), a vibrational molecular fingerprinting tool, is emerging as an economic alternative. Although gas SRS scattering cross sections are only on the order of 10$$^{-31}$$ cm$^2$/sr, considerable progress in the development of enhancement techniques has been made over the past decade. The purpose of this work is to review SRS enhancement approaches in the context of established human breath tests, and to provide a comparison with alternatives. Already, numerous trace gases such as H$$_2$$, CH$$_4$$, $$^{13}$$CO$$_2$$, and volatile organic compounds like acetone can be rapidly quantified in breath at concentrations below 1 ppm with SRS. With improvements in resolution and design of enhancement systems, SRS-based sensors could be scalably deployed in, e.g., pharmacies, and non-invasively screen for dozens of analytes at the parts-per-billion level.
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- Award ID(s):
- 2116275
- PAR ID:
- 10532220
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- TrAC Trends in Analytical Chemistry
- Volume:
- 177
- Issue:
- C
- ISSN:
- 0165-9936
- Page Range / eLocation ID:
- 117791
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1016/j.trac.2024.117791
