Thompson Bruce T, Inberg A, Croitoru N, Mizaikoff Boris
Brown & Williamson Tobacco Corp., P.O. Box 1056, Macon, Georgia 31202, USA.
Appl Spectrosc. 2006 Mar;60(3):266-71. doi: 10.1366/000370206776342661.
Infrared spectroscopy is commonly applied to the analysis of small gas-phase molecules. One of the limitations of using Fourier transform infrared (FT-IR) spectroscopy for these applications is the time response of long path length gas cells. Hollow waveguides (HW) that transmit in the mid-infrared spectral range have higher optical efficiencies compared to long path length cells due to smaller cell volumes. This study characterizes a silver coated, 2 mm inner diameter HW for the analysis of carbon monoxide (CO) and nitric oxide (NO) and compares the performance to a 3 m gas cell and traditional gas analyzers. The HW was found to have a CO response time less than the NDIR analyzer and approximately one-tenth of the response time on the FT-IR system equipped with a 3 m gas cell. The utility of the increased response time was demonstrated by measuring CO concentrations in sidestream cigarette smoke at the same temporal resolution as an NDIR analyzer. A 10 to 60% increase in sensitivity using various frequencies for both CO and NO was observed using the HW compared to the 3 m multipass gas cell. However, cost savings for gas-sensing applications can be achieved on a per analyte basis by using FT-IR spectroscopy, especially in combination with a HW gas-sensing module, which is significantly less expensive than a multipass gas cell.
红外光谱法通常用于分析小的气相分子。对于这些应用而言，使用傅里叶变换红外（FT-IR）光谱法的局限性之一是长光程气室的时间响应。由于气室体积较小，在中红外光谱范围内传输的中空波导（HW）与长光程气室相比具有更高的光学效率。本研究对一种内径为2 mm的镀银HW进行了表征，用于分析一氧化碳（CO）和一氧化氮（NO），并将其性能与一个3 m气室和传统气体分析仪进行了比较。结果发现，HW对CO的响应时间比非分散红外（NDIR）分析仪短，约为配备3 m气室的FT-IR系统响应时间的十分之一。通过以与NDIR分析仪相同的时间分辨率测量侧流香烟烟雾中的CO浓度，证明了响应时间缩短的实用性。与3 m多程气室相比，使用HW对CO和NO在不同频率下的灵敏度提高了10%至60%。然而，通过使用FT-IR光谱法，尤其是与HW气敏模块结合使用，在气体传感应用中可以在每种分析物的基础上实现成本节约，HW气敏模块比多程气室便宜得多。
