Gas analysis by vacuum FTIR – measurement of low concentration gases
November 9, 2022
Introduction
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 the instrument, even with nitrogen purging. It is especially difficult to analyze NO gas because the absorption band is in the water vapor region, and NO2, CO2 and CO gas, whose absorption bands are near the CO2 absorption. Using a full-vacuum instrument system, the water vapor and carbon dioxide in the light path can be completely eliminated and the measurement of these gas components can be accomplished even with low concentrations.
Figure 1 shows the spectrum of a 2 ppm CO sample measured using a 20m gas cell, demonstrating that the 2 ppm CO gas can be 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.
Condition
- Resolution: 4 cm-1
- Scans: 500
- Detector: MCT
- Cell: 20 m pathlength gas cell
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