Webber M E, Claps R, Englich F V, Tittel F K, Jeffries J B, Hanson R K
Appl Opt. 2001 Aug 20;40(24):4395-403. doi: 10.1364/ao.40.004395.
Measurements of NH(3) and CO(2) were made in bioreactor vent gases with distributed-feedback diode-laser sensors operating near 2 mum. Calculated spectra of NH(3) and CO(2) 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(-1) was selected for trace gas monitoring. For CO(2), an isolated transition at 5007.787 cm(-1) 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(3) and 40 ppm for CO(2). We report on the quasi-continuous field measurements of NH(3) and CO(2) 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.
使用工作在2μm附近的分布反馈二极管激光传感器对生物反应器排放气体中的NH₃和CO₂进行了测量。利用计算得到的NH₃和CO₂光谱来确定吸收传感器进行检测的最佳跃迁。对于氨，选择了5016.977 cm⁻¹处一个强且孤立的吸收跃迁用于痕量气体监测。对于CO₂，选择了5007.787 cm⁻¹处一个孤立跃迁来测量变化范围很大的浓度（500 ppm至10%），对于低摩尔分数有足够的信号，对于高摩尔分数又不会光学厚度过大。使用直接吸收和一个总光程为36米的多通流通池，我们实现了NH₃的最低检测限为0.25 ppm，CO₂的最低检测限为40 ppm。我们报告了在NASA约翰逊航天中心，使用便携式自动化传感器系统，在45小时的数据采集窗口内记录的生物反应器排放气体中NH₃和CO₂浓度的准连续现场测量结果。
