Measurements of NH<sub>3</sub> and CO<sub>2</sub> were made in bioreactor vent gases with distributed-feedback diode-laser sensors operating near 2 μm. Calculated spectra of NH<sub>3</sub> and CO<sub>2</sub> were used to determine the optimum transitions for interrogating with an absorption sensor. For ammonia, a strong and isolated absorption transition at 5016.977 cm<sup>−1</sup> was selected for trace gas monitoring. For CO<sub>2</sub>, an isolated transition at 5007.787 cm<sup>−1</sup> was selected to measure widely varying concentrations [500 parts per million (ppm) to 10%], with sufficient signal for low mole fractions and without being optically thick for high mole fractions. Using direct absorption and a 36-m total path-length multipass flow-through cell, we achieved a minimum detectivity of 0.25 ppm for NH<sub>3</sub> and 40 ppm for CO<sub>2</sub>. We report on the quasi-continuous field measurements of NH<sub>3</sub> and CO<sub>2</sub> concentration in bioreactor vent gases that were recorded at NASA Johnson Space Center with a portable and automated sensor system over a 45-h data collection window.
© 2001 Optical Society of America
Michael E. Webber, Ricardo Claps, Florian V. Englich, Frank K. Tittel, Jay B. Jeffries, and Ronald K. Hanson, "Measurements of NH3 and CO2 with Distributed-Feedback Diode Lasers Near 2.0 μm in Bioreactor Vent Gases," Appl. Opt. 40, 4395-4403 (2001)