Infrared (IR) and FTIR Gas Analysis

How does IR and FTIR spectroscopy work?

Many gases absorb infrared (IR) light at their own specific wavelengths; this absorption acts like the gas's "fingerprint". By measuring at which wavelengths and by how much infrared light passing through a gas cell is attenuated, the type and concentration of the gas can be determined.

An FTIR (Fourier transform infrared) spectrometer passes light through an interferometer and examines all wavelengths simultaneously. The resulting signal is converted to a spectrum by Fourier transform. The spectrum of a multi-component mixture is compared with a library of component spectra to calculate the concentration of each gas. Portable IR analyzers use a variable wavelength filter and a multi-pass long-path gas cell; measurement is at a single wavelength or for multiple components from the library.

Optical gas imaging

Infrared absorption is also used to image gas leaks. Optical gas imaging (OGI) cameras capture the light absorbed by gas in a specific wavelength band, making invisible gas clouds visible. This method is used in leak surveys for methane, CO₂ and many VOCs.

What IR and FTIR measures and where it is used

IR and FTIR methods have a wide range of applications:

• Workplace exposure, industrial hygiene and measurement before confined space entry
• Leak detection and LDAR inspections
• Multi-component analysis in emission and process gases
• Process quality control applications such as CO₂ purity monitoring

Where IR and FTIR works well and where it struggles

Dozens or even hundreds of gases and vapors can be measured with one instrument. The method does not alter the sample and needs no additional reagent. New components can be added through library updates.

Limitations: strong absorbers such as water vapor and CO₂ can interfere with the measurement of some components; spectrum analysis takes these effects into account. Symmetrical gases (O₂, N₂, H₂) cannot be measured in the infrared. Multi-pass gas cells and optics are sensitive to contamination and need regular zeroing.

Choosing an instrument for IR and FTIR

When selecting, whether the application is fixed or portable, whether target components are in the library, the measurement range and hazardous area classification are taken into account. For leak surveys, the camera's detection capability is assessed together with the temperature and wind conditions of the measurement environment.

Tetra and IR/FTIR solutions

Tetra supplies, commissions and services infrared-based analysis and imaging solutions in Türkiye. The product range includes the Thermo Scientific MIRAN SapphIRe portable IR gas analyzer and the Opgal EyeCGas Multi OGI gas leak camera. Tetra also prepares FTIR-based CO₂ impurity monitoring systems as part of process gas analysis systems.