Grantee Research Project Results
Final Report: Fourier Transform Infrared Phase Shift Cavity Ring Down Spectrometer
EPA Contract Number: EPD11038Title: Fourier Transform Infrared Phase Shift Cavity Ring Down Spectrometer
Investigators: Dupuis, Julia Rentz
Small Business: OPTRA Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2011 through August 31, 2011
Project Amount: $79,638
RFA: Small Business Innovation Research (SBIR) - Phase I (2011) RFA Text | Recipients Lists
Research Category: SBIR - Air and Climate
Description:
OPTRA Inc. proposed a Fourier transform infrared phase shift cavity ring down spectroscopy (FTIR-PS-CRDS) system for high sensitivity detection of air toxic compounds. Its system operates in the 700 to 1400 cm-1 spectral range wherein lie vapor phase resonance bands for most air toxic compounds and hazardous chemicals. The spectral resolution is 4 or 16 cm-1, depending on the discrimination requirements. OPTRA's approach differs from previous FT-PS-CRDS systems as it has eliminated the external modulator and lock-in detection electronics. OPTRA's system also is the first to be demonstrated in the infrared. Historically, FT-PS-CRDS systems measure a phase delay incurred by light traversing a resonant cavity; the phase delay is in proportion to the product of the ring down time and the modulation frequency. Instead, OPTRA measures the spectrally dependent phase delay of the modulation frequencies imposed by the interferometer itself. This approach is simpler than previous FT-PS-CRDS systems and represents a significant cost reduction without the external modulator. In addition, this approach produces the entire FTIR-PS-CRDS spectra in a single rapid scan, making the technique truly real time and significantly faster than previous techniques. Based on radiometric projections, OPTRA's FTIR-PS-CRDS system will be capable of ppb detection limits with an integration time of 1 second.
Under the Phase I effort, OPTRA designed, built, tested and demonstrated a breadboard FTIR-PS-CRDS system operating in the 700-1400 cm-1 spectral range and thereby established the feasibility of the proposed approach. Phase II plans will include concepts for sensitivity enhancements and the development of a full-scale prototype.
Summary/Accomplishments (Outputs/Outcomes):
OPTRA established the feasibility of the FTIR-PS-CRDS concept via a breadboard design, build, and test. Investigators verified that the FTIR phase spectrum can be used to identify and ultimately quantify trace levels of any analyte that exhibits spectral resonance in the 700 to 1400 cm-1 spectral range. Because most organic and many inorganic hazardous air pollutants do exhibit spectral resonance features in this range, this device is extremely broadly inclusive. As part of the design work, the Phase I effort generated a series of analytical models to predict the overall performance and indicate the trade offs. The modeling indicated a number of areas for sensitivity enhancements to be realized in a Phase II prototype device. The combination of the breadboard results and the analytical models suggests a very sensitive and broadly inclusive trace gas detection system.
Commercialization:
The technology developed under this SBIR project offers significant advantages over commercially available CRDS systems operating in the near IR (NIR). The FTIR-PS-CRDS approach can simultaneously measure a broad range of compounds – both organic and inorganic – at very low concentrations in a single phase spectrum acquired over a sub-second integration time. Commercially available NIR CRDS systems typically require a separate laser per compound and multiple systems are required to cover the same range of compounds the FTIR-PS-CRDS system is capable of detecting. Moreover, NIR systems measure electronic transitions that are not always specific to the molecule and can be confused by spectral interferents. The midwave infrared (MWIR) spectra measured by the FTIR-PS-CRDS system are unique to the molecule and therefore can be used to identify molecules unambiguously and quantify the concentrations, even in the presence of spectral interferents. NIR spectral features also are weaker than MWIR spectral features. For these reasons, OPTRA’s FTIR-PS-CRDS system represents a significant advancement in the state of the art in CRDS. This approach can be thought of as a sensitivity enhancement to traditional FTIR spectroscopy or a spectral range enhancement to traditional CRDS systems.
Potential commercial applications include high sensitivity detection of air toxic compounds, chemical warfare agents, and other hazardous chemicals; industrial monitoring; process monitoring and environmental sensing.
Conclusions:
The FTIR-PS-CRDS technique is feasible and offers many benefits over commercially available CRDS systems that operate in the NIR spectral range. These benefits include broader inclusivity of a wide range of molecules and the ability to simultaneously detect and discriminate among them. To the best of OPTRA's knowledge, this is the first demonstration of FTIR-PS-CRDS using the FTIR as the modulator and also the first demonstration of broadband CRDS in the 700 to 1400 cm-1 spectral range. This approach also offers a considerable measurement bandwidth and cost and complexity advantage over previously executed FTS-PS-CRDS measurements made using an external modulator and lock-in amplifier.
The Phase I effort set the stage for a Phase II development effort to produce a prototype FTIR-PS-CRDS system with enhanced sensitivity to detect a broad range of compounds at part-per-billion detection levels. The Phase II prototype also will realize a more “product-like” form factor.
SBIR Phase II:
Fourier Transform Infrared Phase Shift Cavity Ring Down SpectrometerThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.