通过真空FTIR进行的气体分析——低浓度气体的测量

对于低浓度气体或蒸汽化合物的FT-IR分析，通常需要高信噪比测量。此外，某些气体样品的测量可能会受到仪器中存在的大气水蒸气和二氧化碳的影响，即使是通过氮气净化。由于NO气体的吸收带在水蒸气区，而二氧化氮、二氧化碳和CO气体的吸收带靠近二氧化碳吸收区，因此分析尤其困难。使用全真空仪器系统，可以完全消除光路中的水蒸气和二氧化碳，即使在低浓度下也可以完成这些气体成分的测量。‍Figure 1 illustrates the spectrum of a 2 ppm CO sample by using a 20 m gas cell, demonstrating that the 2 ppm CO gas is measured with a S/N level around 200:1. The noise level with the same measurement conditions is 4 x 10 -5 ABS as displayed in Figure 2, and with this noise level, the measurement of this gas can be easily accomplished with concentrations as low as 20-50 ppb.Application NoteNo.230TR0165-E Analysis Example by Vacuum Model FT/IR (2)Analysis of Low Concentration Gas using Long Pathlength Cell A high S/N measurement is often required for the FT-IR analysis of low concentrations of gas or vapor compounds. In addition，the measurement of certain gas samples can be affected by the atmospheric water vapor and carbon dioxide present in t he instrument， even with nitrogen purging. It is especially di f ficult to analyze NO gas because the absorption band i s in the water vapor regio n ， and NO， CO， and CO gas， whose absorption bands are near the CO， absorption. Using a full-vacuum i nstrument system， the water vapor and carbon dioxide in the light path can be completely eliminated and the measurement of t hese gas components can be accomplished even with low concentrations. Figure 1 illustrates the spectrum of a 2 ppm CO sample by using a 20 m gas cel l ， demonstrating that the 2 ppm CO gas i s measured with a S/N level around 200：1. The noise level with the same measurement conditions is 4 x 105 ABS as displayed i n Figure 2， and wi t h thi s noise level， the measurement of this gas can be easily accompl i shed with concentrations as low as 20-50 ppb. Condition Resolution： 4cm Scans： 500 Detector： MCT Cell ： 20 m pathlength gas cell Fig. 1 2 ppm CO gas Fig.2 Spectrum S/N using the MCT detector