How Does FTIR Analysis Work?

Introduction to FTIR Analysis

FTIR stands for Fourier Transform Infrared Spectroscopy. FTIR Analysis measures the infrared region of the electromagnetic radiation spectrum, which has a longer wavelength and a lower frequency than visible light. This spectrum is measurable in a sample when submitted to infrared radiation (IR). The basic theory at work is that the bonds between different atoms absorb light at different frequencies.

With FTIR testing, the light is measured using an infrared spectrometer which produces the output of an infrared spectrum. The FTIR spectrum is a graph of infrared light absorbance by the substance on the vertical axis and the frequency (wavelength) on the horizontal axis.

How FTIR Works
Pros and Cons of FTIR
FTIR Case Studies
5 FTIR Analysis Techniques
FTIR Testing Process
Additional FTIR Resources
FTIR FAQ

How FTIR Works

FTIR analysis measures the range of wavelengths in the infrared region that are absorbed by a material. This is accomplished through the application of infrared radiation (IR) to samples of a material. The sample’s ability to absorb the infrared light’s energy at various wavelengths is measured to determine the material’s molecular composition and structure.

Unknown materials are identified by searching the IR spectrum against a database that has a wide range of reference spectra. Materials can be quantified using the FTIR materials characterization technique as long as a standard curve of known concentrations of the component of interest can be created.

Fourier Transform Infrared Spectroscopy Analysis can be used to identify unknown materials, additives within polymers, surface contamination on a material, and more. The results of the tests can pinpoint a sample’s molecular composition and structure.

A simple device called an interferometer is used to identify samples by producing an optical signal with all the IR frequencies encoded into it. The signal can be measured quickly.

Then, the signal is decoded by applying a mathematical technique known as Fourier transformation. This computer-generated process then produces a mapping of the spectral information. The resulting graph is the FTIR spectrum which is then searched against reference libraries for identification.

With the microscope attachment, samples as small as 20 microns can be analyzed. This allows quick and cost-effective identification of unknown particles, residues, films or fibers. FTIR testing can also measure levels of oxidation in some polymers or degrees of cure in other polymers as well as quantifying contaminants or additives in materials.

Pros and Cons of FTIR

Pros

Identify compounds as small as 10 to 20 microns
In many cases, analysis does not harm the sample, nor is the sample altered by analysis.
In FTIR analysis, absorbance bands across the mid-Infrared spectrum are measured simultaneously, allowing a lot of analytical information very quickly
Analysis itself can be completed very quickly, as well; Innovatech analysts can complete expedited requests in as little as 24 to 48 hours
Useful for analyzing a wide variety of organic and some inorganic substances
Wavelength measurement is known absolutely, which makes analytical techniques such as spectral subtraction quick and highly accurate

Cons

Because FTIR analysis subjects the sample to all of the mid-infrared frequencies simultaneously, if noise occurs in one part of the radiation from the infrared source, it will spread through the spectrum.
Changes in atmospheric conditions can affect FTIR analysis, making it difficult to use on highly-sensitive samples or samples that must be studied over a long period of time.
FTIR is a bulk analysis method, which makes it best for locating and identifying broad categories of substances in a compound; it is less capable of identifying trace amounts of materials in mixtures with other materials.

FTIR Case Studies & Applications

FTIR analysis has multiple real-world applications. Numerous case studies illustrate how FTIR analysis provides critical insights into material composition and structure, showcasing its utility across various industries.

Forensic Fiber Testing Uses FTIR Techniques to Reveal Foreign Fibers

A medical device company uses FTIR analysis to protect a critical component.
Read the case study

FTIR Analysis Helps Monitor HIV Patients

Researchers explore the use of Fourier Transform Infrared Spectroscopy (FTIR) as a cost-effective alternative for monitoring metabolic changes in HIV patients.
Read the case study

Gemologists Use FTIR to Identify Fake Diamonds

FTIR helps gemologists identify diamonds’ molecular compositions and distinguish between natural and synthetic varieties.
Read the case study

See more FTIR case studies

5 FTIR Analysis Techniques

There are several FTIR analysis sampling techniques that can be used to understand a material’s structure and identify the material, each with their own proficiency:

Attenuated Total Reflectance – In ATR spectroscopy, an infrared beam is guided onto a dense and highly-refractive crystal at a very specific angle. The beam reflects off the crystal and comes into contact with the sample. The testing technique records changes that occur in the reflected beam after it contacts the sample.

ATR spectroscopy only requires that the sample comes into close contact with the ATR crystal, and so minimal or even no sample preparation is required to use it. ATR can be used to analyze a wide variety of solids and, depending on the ATR crystal’s structure, some liquids. It’s particularly useful for analyzing thick or multilayered samples such as paints, rubbers, plastics, or coatings.
Specular Reflectance – Specular reflectance, or SR, spectroscopy involves reflecting an IR beam directly off of the sample surface at such an angle that specular, or singular and direct, reflection occurs (as opposed to diffused reflection).
SR typically occurs when testing glossy, flat, and reflective samples, such as glass and crystal. It is primarily used to evaluate the surfaces of coatings, thin films left on reflective surfaces, or contaminated metal surfaces.

Reflection-Absorption – Infrared Reflection Absorption Spectroscopy (IRAS) measures the amount of a reflected infrared beam that is absorbed as it passes through the sample by measuring the wavelength of the beam after it contacts the sample.
IRAS is used to study thin samples such as residues, plants, or sub-monolayer films left behind on reflective surfaces.

Transmission – Infrared Transmission Spectroscopy works a lot like IRAS, except the infrared radiation passes directly through the gas, liquid or solid samples to be tested. The resulting change in spectrum after the beam passes through the sample gives testers an understanding of what the sample contains.

Like IRAS, Infrared Transmission Spectroscopy is generally used for very thin samples (typically, samples analyzed via Infrared Transmission Spectroscopy may be no thicker than a few ten micrometers. .
Photoacoustic – Infrared Photoacoustic Spectroscopy (PAS) can be difficult, but it’s not impossible. This analysis technique involves intermittently exposing the sample to infrared radiation over time. As the sample absorbs the Infrared radiation, those absorptions are converted to heat inside the sample, creating a photoacoustic signal. By measuring this photoacoustic signal, analysts can determine the structure and make-up of the sample.

PAS is highly useful for evaluating samples in their original, whole forms, so it’s most frequently used on samples that can’t be crushed or exposed to chemicals, such as bone, seashells, and other sensitive organic materials.

What about UV Vis?

UV (ultraviolet) is similar to FTIR analysis in that they both use light. However, ultraviolet light is usually monochromatic, while FTIR uses multiple color frequencies.

FTIR Testing Process

Step 1: Place sample in FTIR spectrometer.

The spectrometer directs beams of IR at the sample and measures how much of the beam and at which frequencies the sample absorbs the infrared light. The sample needs to be thin enough for the infrared light to transmit through, or a thin slice of the material must be removed.

Reflectance techniques can be used on some samples and no damage is done to the sample. Samples conducive to reflectance are residues, stains or films on a fairly flat reflective surface or somewhat pliable materials that are thin enough to fit under the microscope using the attenuated total reflectance attachment to the microscope.

Step 2: Identify the samples.

The reference database houses thousands of spectra, so samples can be identified. The molecular identities can be determined through this process.

FTIR Sampling

Samples as small as 10 microns can be evaluated using FTIR analysis. The tiny sample size allows for cost effective identification of particles, residues, films or fibers. FTIR analysis can also measure levels of oxidation or degrees of cure in some polymers as well as measuring the level of contaminants or additives.

Learn more about FTIR Sampling Techniques.

Additional FTIR Resources

Overview of FTIR Spectroscopy
Learn more about what FTIR is and how it can be used across an array of industries. This informative page describes the pros and cons of FTIR testing, as well as Innovatech Labs’ FTIR services, including the FTIR analysis process, requirements for a sample, testing capabilities and more.
FTIR Applications and Service Details
More information on specific industry applications of FTIR testing, and how to find out if FTIR testing is right for your analysis needs.
FTIR Resources and Learning Materials
Interested in studying FTIR without the student ID? Learn how to find FTIR tutorials, reference books, manuals, software and database bundles. With information and links to further study, this page will help you get started.
FTIR Sampling Techniques
Discover some of the FTIR analysis methods used by scientists, university researchers and Innovatech’s own analysts to test samples.

FTIR FAQ

What is FTIR?

Fourier Transform Infrared spectroscopy (FTIR) measures the infrared region of the electromagnetic radiation spectrum, which has a longer wavelength and a lower frequency than visible light. This spectrum is measurable in a sample when submitted to infrared radiation (IR). The basic theory at work is that the bonds between different atoms absorb light at different frequencies.

How does FTIR work?

With FTIR testing, the light is measured using an infrared spectrometer which produces the output of an infrared spectrum. The FTIR spectrum is displayed as a chart. The vertical axis shows how much infrared light the substance absorbs. The horizontal axis represents the frequency, or wavelength, of the light.

Here’s a breakdown:

Infrared Radiation: FTIR analysis exposes a sample to infrared light. This light has a longer wavelength and a lower frequency than visible light.
Molecular Absorption: Different molecular bonds within the sample absorb specific frequencies of this infrared light. This absorption happens because the energy of the infrared light causes the molecules to vibrate.
Spectrum Generation: The spectrometer in an FTIR system measures the light that passes through the sample and the light that’s absorbed. It uses this information to create a spectrum, which is essentially a graph showing the different frequencies of infrared light absorbed by the sample.
Data Interpretation: By analyzing the absorption pattern (spectrum), scientists can determine what types of bonds are present in the sample. This helps identify the material’s molecular structure and composition.

What does FTIR measure?

What is FTIR analysis used for?

FTIR Analysis can be used to identify unknown materials, additives within polymers, surface contamination on a material, and more. The results of the tests can pinpoint a sample’s molecular composition and structure.

How do you analyze FTIR results?

The x-axis—or horizontal axis—represents the infrared spectrum, which plots the intensity of infrared spectra. The peaks, which are also called absorbance bands, correspond with the various vibrations of the sample’s atoms when it’s exposed to the infrared region of the electromagnetic spectrum. For mid-range IR, the wave number on the infrared spectrum is plotted between 4,000 to 400 cm-1. The y-axis—or vertical axis—represents the amount of infrared light transmitted or absorbed by the sample material being analyzed.

The absorbance bands seen when a material absorbs the infrared light are typically grouped within two types: group frequencies and molecular fingerprint frequencies.

Group frequencies are characteristic of small groups of atoms or functional groups such as CH₂, OH, and C=O. These types of bands are typically seen above 1,500cm-1 in the infrared spectrum and they’re usually unique to a specific functional group, making them a reliable means of identifying functional groups in a molecule.

As for fingerprint frequencies, these are highly characteristic of the molecule as a whole; they tell what is going on within the molecule. These types of absorbances are typically seen below 1500cm-1 in the infrared spectrum; however, some functional groups will absorb in this region as well.

As a result, this region of the spectrum is less reliable for identification, but the absence of a band is often more indicative than the presence of a band in this region. For more information, read: A Beginner’s Guide to FTIR Analysis: Interpreting & Analyzing Results

What is the difference between IR and FTIR?

The difference between IR and FTIR is that IR uses a monochromatic system, which takes the absorption of the monochromatic IR light at a time and plots the spectrum.

FTIR uses a Michelson interferometer, which measures the interference of waves, such as light or radio waves. The interferometer creates a beam of different frequencies of light at once. It then determines how much of that beam is absorbed by the sample to construct an interferogram as the raw signal.

The interferogram represents the light intensity as a function of the position of the mirror in the Michelson interferometer, not as a function of wavelength as occurs in dispersive IR instruments. The signal is this “Fourier Transformed” to produce the intensity as a function of wavenumber. FTIR is a more effective and faster analytical technique compared to IR.

What are the advantages of FTIR?

FTIR is the go-to technique in many instances. Very little material is needed for an analysis and the analysis is relatively quick and inexpensive compared to other analytical techniques.

FTIR can be used to identify solids, liquids or gasses. Attenuated total reflectance FTIR allows the surface of a material to be analyzed when looking at multi-layered compounds, coatings or even thin films of a foreign material on a surface. With hundreds of thousands of reference spectra available, identification of the class of the primary component of a compound is highly likely.

What are the most important FTIR sampling techniques?

Attenuated Total Reflectance (ATR) is the most common FTIR sampling technique. This can be done using a horizontal ATR accessory on a bench or using an ATR objective on a microscope attachment to an FTIR. ATR allows the sample to be analyzed with minimal sample prep, with creating intimate contact with the sample the only constraint for this technique.

Other techniques of sampling include reflectance, where a material on a reflective surface can be analyzed in situ, transmittance, where the IR beam is shone through a thin slice of the material, diffuse reflectance, which is used for powders and rough surface solids, and specular reflectance, which is used for samples with reflective surfaces.