Fourier transform infrared spectroscopy (FTIR) is a quick, simple, and efficient technique for identifying and quantifying the constituent elements in any sample. The capacity to identify and quantify nearly any gas, coupled with its resilience and accuracy, makes FTIR gas analysis technology suitable for a wide range of commercial uses.
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A Brief Overview of FTIR Gas Analyzers
Infrared spectroscopy is the study of how infrared photons interact with materials through absorption, emission, or reflection. Fourier Transform Infrared gas analyzers evaluate the absorption of infrared light by gases to determine the concentration of gases in any specimen.
FTIR gas analyzers efficiently scan the entire infrared spectrum of the entire specimen simultaneously. The interference pattern created by the sensor, known as an "interferogram," encapsulates all essential information evaluated across all wavelengths and the signal is subjected to Fourier transform. The computer software performs the necessary computations and displays the IR spectrum to the user.
Industrial Utilization of FTIR Gas Analyzers
FTIR gas analyzers are used in a variety of fields, including environmental monitoring, industrial process control, and automotive research. In environmental monitoring, FTIR gas analyzers can be used to measure the concentrations of greenhouse gases, such as carbon dioxide and methane, in the atmosphere. In industrial process control, FTIR gas analyzers can be used to monitor the concentrations of gases in industrial processes, such as the production of chemicals or petrochemicals.
Working Principles of FTIR Gas Analyzers
The concept of infrared absorption spectroscopy is utilized by FTIR gas analyzers. Infrared absorption spectroscopy is a technique that involves passing a beam of infrared radiation through a sample and measuring the amount of infrared radiation that is absorbed by the sample.
For almost seventy years, IR spectroscopy has served as a standard method for materials characterization in the laboratory. An infrared spectrum is a sample's identity, with absorption peaks corresponding to the frequency of oscillations between the bonding of the atoms that make up the material. Each molecular complex is made up of a distinct combination of atoms, so no chemical products exhibit the same infrared spectrum. As a result, infrared spectroscopy can provide an accurate assessment (qualitative analysis) of the unique composition of any substance.
To measure the concentration of gases in a sample using an FTIR gas analyzer, the sample is placed in the path of the infrared beam, and the absorption spectrum of the sample is measured. The resulting absorption spectrum is then analyzed using specialized software to determine the concentration of each gas present in the sample. The concentration of each gas is calculated by comparing the absorbance of the gas at specific wavelengths to the absorbance of a reference gas with a known concentration.
Components of FTIR Gas Analyzers
A typical FTIR spectrometer is made up of an IR source, an interferometer, a specimen compartment, a sensor, an amplification system, an A/D converter, and microprocessor software.
A wideband emitter, such as a mid-IR ceramic device or a far-IR mercury lamp, is commonly used as the source. The interferometer, which comprises a beam-splitter, a static reflector, a mobile mirror, and a timed laser, is the core component of an FTIR analyzer. The beam-splitter divides light from a source into two channels, one with a fixed mirror and the other with a movable mirror. The light is directed through the specimen and onto a sensor, where it is transformed from the time domain to the frequency domain using a Fast Fourier Transform.
Advantages and Limitations of FTIR Gas Analyzers
FTIR gas analyzers are highly sensitive and can detect trace amounts of gases down to parts-per-billion (ppb) levels. They can measure multiple gases simultaneously, making them suitable for analyzing complex gas mixtures. Simple operational methods and affordable maintenance of FTIR analyzers are major advantages over traditional methods. They do not require frequent calibrations and are versatile enabling their use in a wide range of applications.
FTIR gas analyzers might seem the best fit, however, several limitations exist. FTIR gas detectors are very costly when contrasted to other analytical methods such as gas chromatography (GC) and mass spectrometry (MS). They are ineffective for evaluating some substances, such as water vapors, which absorb infrared radiation scarcely. Additionally, for some applications such as those in the semiconductor sector, where very precise detection limits are necessary, the sensitivity of FTIR analyzers raises a big concern.
Recent research published in the journal Case Studies in Thermal Engineering provides data regarding the gas emission characteristics of nitrification waste using thermos-gravimetric analysis coupled with Fourier transform infrared spectrometry (TG-FTIR). In the contemporary chemical industry, nitrification is a crucial process. Nitro groups (-NO2) are introduced into organic molecules in this aggressive exothermic process.
It was found that the thermal degradation of nitrification waste took place in three phases. Physical reactions including vaporization influenced stage I, while chemical thermal degradation predominated phases II and III.
When nitrification waste was heated at a rate of 8°C/min with oxygen levels of 21% and 15%, the products were thermally decomposed, and the FTIR spectra of these products revealed clear gas absorption peaks at high temperatures (about 300°C). The FTIR analyzer spectra revealed stage 1 consisting of CO2 and H2O peaks while stage 2 consisted of relatively higher CO2 amounts. However, in stage 3 large quantities of CO2 were released along with spectra corresponding to NO2 indicating the decomposition of nitrous waste.
The findings of this study can improve our understanding of the thermal behavior of nitrification material and provide the basis for an efficient framework to prevent thermal hazards.
Researchers have developed new techniques for improving the accuracy and precision of FTIR gas measurements, such as improved data processing algorithms and the use of reference gas standards. There has been a push towards the development of portable, miniaturized FTIR gas analyzers for use in field measurements and remote monitoring applications. Additionally, there has been a lot of interest in the use of quantum cascade lasers (QCLs) in FTIR gas analyzers has increased in recent years due to their high power and stability. All these steps would ensure the success of FTIR analyzers in the coming years.
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References and Further Reading
Gasmet, 2023. FTIR – Fourier Transform Infrared. [Online]
Available at: https://www.gasmet.com/
[Accessed 7 January 2023].
Tang, Y. et. al. (2022). Thermokinetics and gas emission characteristics of nitrification waste under different oxygen contents by using TG-FTIR technique. Case Studies in Thermal Engineering, 102689. Available at: https://doi.org/10.1016/j.csite.2022.102689
JASCO, 2023. Fundamental Theory and Applications of FTIR Spectroscopy. [Online]
Available at: https://jascoinc.com/learning-center/theory/spectroscopy/fundamentals-ftir-spectroscopy/
[Accessed 7 January 2023].
Thain, S., 2022. IR Spectroscopy and FTIR Spectroscopy: How an FTIR Spectrometer Works and FTIR Analysis. [Online]
Available at: https://www.technologynetworks.com/analysis/articles/ir-spectroscopy-and-ftir-spectroscopy-how-an-ftir-spectrometer-works-and-ftir-analysis-363938
[Accessed 6 January 2023].
Giechaskiel, B.; Clairotte, M. (2021). Fourier Transform Infrared (FTIR) Spectroscopy for Measurements of Vehicle Exhaust Emissions: A Review. Appl. Sci. 11. 7416. Available at: https://doi.org/10.3390/app11167416
ThermoFisher Scientific, 2022. Introduction to Gas Phase FTIR Spectroscopy. [Online]
Available at: https://assets.thermofisher.com/TFS-Assets/MSD/brochures/gas-phase-ftir-spectroscopy-introduction-BR52338.pdf
[Accessed 6 January 2023].
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