FTIR Explained
What is FTIR?
Fourier Transform Infrared (FTIR) spectroscopy is a technique used to obtain an infrared spectrum of absorption, emission, or other properties of a sample. This technology is based on the Fourier Transform mathematical method, which converts complex signals into a spectrum of frequencies. FTIR is commonly applied in chemical analysis to identify and quantify organic compounds, pharmaceuticals, polymers, and environmental samples by analyzing the molecular vibrations within a sample.
FTIR spectroscopy is widely used for gas analysis, offering a fast, sensitive, and non-destructive means of detecting and quantifying gases in various applications, including environmental monitoring, industrial processes, and laboratory analysis. FTIR gas analysis relies on the principle that gases absorb specific frequencies of infrared light based on their molecular structure, allowing the identification and quantification of multiple gases in a single measurement.
How FTIR Works
Infrared Source: An FTIR instrument emits a broad spectrum of infrared light that passes through a beam splitter, which divides the light into two separate beams. One beam reflects off a moving mirror, while the other reflects off a stationary mirror.
Interferometer: The beams from the two mirrors are recombined to create an interference pattern or interferogram, which captures all the infrared light absorbed and emitted by the sample across a wide range of wavelengths simultaneously.
Sample Interaction: The combined infrared light beam is directed at the sample. When the sample absorbs specific frequencies, the energy is used to cause molecular vibrations, such as stretching or bending of chemical bonds. Different molecular structures absorb infrared light at different, characteristic wavelengths, producing a unique spectral fingerprint.
Detector and Interferogram Analysis: The light that has interacted with the sample passes to a detector, which records the intensities over time as the mirror moves. This data forms an interferogram that contains the complete spectral information of the sample but in the time domain.
Fourier Transformation: The interferogram is then mathematically converted into a spectrum using the Fourier Transform. This transformation translates the time-domain signal into a frequency-domain spectrum, displaying the intensities of absorption at different wavelengths.
Spectrum Output: The resulting spectrum shows peaks corresponding to different molecular vibrations, which can be analyzed to identify the sample's molecular composition. Peaks correspond to specific functional groups or bonds within the molecules, and the pattern of these peaks serves as a molecular fingerprint for identification and quantification.
How FTIR Gas Analysis Works
Infrared Light Source and Interferometer: The FTIR instrument generates infrared light and splits it using an interferometer, similar to other FTIR applications. This split beam is recombined to create an interferogram that contains information across a broad range of infrared frequencies.
Gas Sample Cell: The infrared beam is directed through a gas sample cell, which is designed to optimize the path length of the light through the gas, enhancing the instrument’s sensitivity. The sample cell can be heated or cooled to control conditions, especially for volatile compounds or gases that condense easily.
Molecular Absorption: As the infrared beam passes through the gas, molecules in the sample selectively absorb specific frequencies of the infrared light based on their chemical bonds. Each gas molecule has a unique absorption pattern, creating a distinct spectral "fingerprint."
Detector and Fourier Transformation: The beam emerging from the sample cell reaches a detector, which records the intensities of light at each wavelength. This raw data forms an interferogram, which is then converted into a spectrum by Fourier Transform. The resulting spectrum displays peaks corresponding to the specific frequencies absorbed by the gas molecules.
Spectral Analysis: By comparing the measured absorption peaks against known reference spectra for different gases, the FTIR system can identify which gases are present. The intensity of each peak corresponds to the concentration of that gas, allowing for quantification.
Real-Time Monitoring: FTIR gas analyzers can continuously monitor gas concentrations, making it possible to track changes over time. This is beneficial for real-time monitoring in industrial or environmental settings, where gas levels can vary significantly and require quick response.
Advantages of FTIR Technology
- Speed: FTIR captures all wavelength information at once, unlike traditional dispersive spectrometers, making it faster.
- Resolution: The use of interferometry and Fourier Transform allows for high spectral resolution and accuracy.
- Sensitivity: FTIR is highly sensitive, enabling the detection of low concentrations of compounds. FTIR is capable of detecting trace gases at very low concentrations with accuracy.
- Non-Destructive: FTIR can often analyze samples without altering or damaging them, which is beneficial for certain applications, like biological or art conservation analysis.
- Multi-Component Analysis: FTIR can detect and quantify multiple gases simultaneously in a single measurement.
- Real-Time Monitoring: It provides rapid analysis, which is crucial for time-sensitive applications like emissions monitoring.
Key Applications of FTIR Gas Analysis
Environmental Monitoring:
- Air Quality: FTIR is used to monitor pollutants like carbon monoxide, nitrogen oxides, sulfur dioxide, and volatile organic compounds (VOCs) in air quality monitoring stations.
- Greenhouse Gases: It is commonly applied to detect greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, which are critical in climate change research.
- Industrial Process Control: Combustion Analysis: FTIR can analyze exhaust gases in combustion processes, providing information on emissions for regulatory compliance and process optimization.
- Chemical Manufacturing: In chemical plants, FTIR is used to monitor reaction by-products and to ensure safe levels of potentially hazardous gases.
- Petroleum and Gas Industry: FTIR detects hydrocarbon gases in oil refineries and gas processing facilities, helping to monitor for leaks and optimize refining processes.
Medical and Biotechnological Applications:
- Respiratory Gas Analysis: FTIR is used in healthcare to analyze exhaled breath, aiding in the detection of metabolic or respiratory conditions.
- Biogas Analysis: FTIR monitors biogas production, including methane and other gases, which is important in renewable energy generation.
Laboratory and Research:
- Chemical Research: FTIR is essential for research in gas-phase chemical reactions, providing insights into reaction mechanisms and kinetics.
- Academic Research: FTIR aids in atmospheric research and environmental science studies, including real-time analysis of gases in controlled environments.
Gasmet Feature
Gasmet is a company based in Finland. Their technology was developed at a University in Finland in the early 1990s. Their technology is based on Fourier Transform Infared (FTIR). They didn’t invent FTIR technology, what they did was perfected it. They have developed methods to lower the detection limits of FTIR into the lower PPB range, for over five thousand gases. They also have developed the ability to take FTIR technology out of the lab and put it in both a portable instrument for industrial hygiene and hazmat applications and also into CEMS systems they can be directly mounted onto a smokestack.
They have ruggedized the FTIR technology to take it out of the lab and into the field. They also have unique software that will notify a user if the current library of gases doesn’t match the gases in the sample. The instruments can measure up to fifty gases at a time. If there’s a fifty first or fifty second gas also present, the instrument will mark that in the results as an error.
The end user can do a search of the recorded spectra from the sample that was taken, identify the other gases that are there, load those gases into the library and continue to do measurements in real time. It’s the only portable FTIR analyzer that can go into the field and take continuous real time measurements down into the PPB range without any cross sensitivity.
Go to: ETAPII's Gasmet Company Page
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