Abstract. Simultaneous measurement of C2H6 and CH4
concentrations, and of the δ13C-CH4 isotope ratio is
demonstrated using a cavity-enhanced absorption spectroscopy technique in
the mid-IR region. The spectrometer is compact and has been designed for
field operation. It relies on optical-feedback-assisted injection of
3.3 µm radiation from an interband cascade laser (ICL) into a V-shaped
high-finesse optical cavity. A minimum absorption coefficient of 2.8×10-9 cm−1 is obtained in a single scan (0.1 s) over 0.7 cm−1. Precisions of 3 ppbv, 11 ppbv, and 0.08 ‰ for
C2H6, CH4, and δ13C-CH4, respectively, are
achieved after 400 s of integration time. Laboratory calibrations and tests
of performance are reported here. They show the potential for the
spectrometer to be embedded in a sensor probe for in situ measurements in ocean
waters, which could have important applications for the understanding of the
source and fate of hydrocarbons from the seabed and in the water column.
Simultaneous Detection of C2H6, CH4 and δ13C-CH4 Using Optical Feedback Cavity Enhanced Absorption Spectroscopy in the Mid-Infrared Region: Towards Application for Dissolved Gas Measurements