Gas analysis by vacuum FTIR – measurement of low concentration gases

Download PDF November 9, 2022


FTIR-4000 and 6000 Spectrometers
FTIR-4000 and 6000 Spectrometers

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.

Fig 1. 2 ppm CO gas
Fig 2. Spectrum S/N using an MCT detector


  • Resolution: 4 cm-1
  • Scans: 500
  • Detector: MCT
  • Cell: 20 m pathlength gas cell

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About the Author

Dr. Carlos Morillo received his Post Doc at Advanced Industrial Science & Technology in Fukuoka and was a Research Scientist at Kyushu University in Japan where he lived for several years. Carlos received his Doctor of Engineering from Kyushu University and his Masters and BS from Simon Bolivar University in Caracas Venezuela. He is an Applications Scientist at JASCO.