Simultaneous detection of Csub2/subHsub6/sub, CHsub4/sub, and iδ/isup13/supC-CHsub4/sub using optical feedback cavity-enhanced absorption spectroscopy in the mid-infrared region: towards application for dissolved gas measurements

摘要

Simultaneous measurement of Csub2/subHsub6/sub and CHsub4/sub concentrations, and of the δsup13/supC - CHsub4/sub 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 μ m 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 sup?1/sup is obtained in a single scan (0.1?s) over 0.7?cm sup?1/sup . Precisions of 3?ppbv, 11?ppbv, and 0.08?‰ for Csub2/subHsub6/sub , CHsub4/sub , and δsup13/supC - CHsub4/sub , 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.