FTIR (Fourier Transform Infrared) spectrometers are innovative devices used in polymer science, organic synthesis, pharmaceutical industries, petrochemical engineering, and food analysis. Aside from these various applications, they are also commonly combined with chromatography to detect unstable substances in different chemical reaction mechanisms.

Let’s talk about what an FTIR spectroscopy instrument is, its components and how they function, and the application of this machine in various fields. 

What is an FTIR Spectroscopy Instrument?

Agilent FTIR spectroscopy instruments utilize FTIR analysis, an analytical content for identifying organic, inorganic, and polymeric materials. These machines use infrared light in scanning test samples to observe their chemical properties. 

The FTIR spectroscopy instrument became one of the most utilized machines because different chemical molecules and substances can produce various spectral fingerprints. It mainly converts the output from the detector into a spectrum that can be interpreted and formulates patterned spectra with structural insights. 

How does an FTIR Spectroscopy Instrument Work?

What Is FTIR Spectroscopy Instrument and How It Operates

The main components of an FTIR spectroscopy instrument are the source, the interferometer, and the detector. To get the most accurate readings, make sure that all these components are working efficiently. 

Light Source 

The light source is a broadband emitter and is typically a mid-IR ceramic source, a far-infrared mercury lamp, or a near-infrared halogen lamp. 

Michelson Interferometer

The interferometer is the most important component of the FTIR spectroscopy instrument, and it’s based on the Michelson Experimental Setup. It consists of a beam splitter and two mirrors: one fixed and one translating forward and backward. The beam splitter is responsible for transmitting half of the radiation it receives and reflecting the remaining half. 

When the radiation strikes the beam splitter, it divides into two separate beams. One of these separated beams is transmitted to the fixed mirror, and the other beam to the translating mirror. These two mirrors will reflect back the radiation to the beam splitter. 

The reflected radiation is again halved, with one half transmitted and the other half reflected by the beam splitter. This results in one beam passing directly to the spectrometer’s detector and the other beam going back to the light source. 


The beam that passes through the detector will be converted to photons and then into measurable electric signals that the computer will read. Several common detectors used are the following:

  • Room temperature DLATGS used for routine analyses
  • Cooled liquid nitrogen used for high-sensitivity applications
  • Si-photodiodes used for near-IR and visible infrared
  • Silicon bolometers for far-infrared

The Purpose and Applications of FTIR Spectroscopy Instrument

The FTIR spectroscopy instrument is widely used in different quality control processes to evaluate industrially-manufactured materials, and FTIR spectroscopy is the common first step in material analysis. A change in the absorption band characteristic patterns in the spectrometer indicates a change in the material composition or possible contamination. 

When a certain product is found to have problems during the visual inspection, the origin of the problem is commonly determined using FTIR microanalysis. This is a common technique for the chemical composition analysis of smaller particles. 

Generally, FTIR spectroscopy instruments are cost-effective machines used for the following:

  1. Identifying and characterizing unknown materials, including films, powders, solids, and liquids.
  2. Identifying the presence of contamination on materials, including particles, powders, fibers, and liquids.
  3. Identifying additives after polymer matrix extraction.
  4. Determining decomposition, oxidation, and uncured monomers in most failure analysis investigations.
  5. Gain kinetic information on the decay or growth of infrared absorptions.

Advantages of FTIR Spectroscopy Instrument 

The FTIR spectroscopy instrument has three main advantages compared to a dispersive infrared spectrometer:

Multiplex Advantage 

The multiplex advantage is an important new development for FT-IRs because it can speed up sample processing and analysis. In FTIR spectroscopy instruments, the interferometer does not need to separate energies and divide them into individual frequencies before obtaining measurements. In the interferogram, each point has information about each light wavelength measured. 

Each stroke is equivalent to one infrared spectrum scan when the moving mirror is struck, and the individual scans are combined for signal averaging. With the traditional dispersive instrument, each wavelength passing across the spectrum should be individually measured, slowing the process down. 

Throughput Advantage

The FTIR spectroscopy instrument does not limit how much light reaches the detector through the slit. It also uses the least number of necessary mirrors, leading to fewer reflective losses. With this, more energy will reach the sample and the detector than a traditional dispersive spectrometer. 

Generally, the higher signals in the FTIR spectrometers also lead to a better signal-to-noise ratio, improving the machine’s sensitivity for smaller absorptions. So, the details in the sample will also be more distinguishable and clearer. 

Precision Advantage

The laser used in an FT-IR spectrometer is the reference signal and timekeeper for this high precision instrument. It also travels at speeds similar to other components within its own system. This can provide accurate readings without being confused by interference from outside sources such as sunlight or ambient temperature fluctuations.

Due to this, the spectra collected from an FTIR spectroscopy instrument can be compared and still get accurate readings even though they are five minutes or five months apart. Unfortunately, this advantage is not available in dispersive infrared systems or the systems that need external calibration standards. 

Interpreting FTIR Spectrograph

Data interpretation in FTIR spectrographs is not straightforward. The total spectrum the machine generates is a series of absorbed energy responses, and the absorbed bands seen on the spectrograph are not completely degenerative and discrete. 

Because the energy peak, as seen on the bands, can move around depending on the matrix and chemical factors, you cannot automatically predict which band the peak belongs to. With this, you must interpret the spectrum as an entire system, and it helps if you seek help from experienced analysts for proper characterization and identification. 

It’s also possible for the FTIR analysis to quantify functional groups with a complete understanding of the chemistry and standard of available reference materials. The graphs show that the absorbance intensity can help correlate to the functionality quantity present in the samples used. 

However, you must still remember that since the FTIR spectroscopy instrument utilizes bulk analytical techniques, it cannot present accurate information in small concentrations. 

Sampling Methods of FTIR Spectroscopy 

What Is FTIR Spectroscopy Instrument and How It Operates

FTIR spectroscopy has four major sampling methods: Attenuated Total Reflectance, transmission, specular reflectance, and diffuse reflectance. 

Attenuated Total Reflectance 

Attenuated total reflectance measures the changes occurring in internally reflected infrared beams when the specific beam comes in direct contact with the sample. The infrared beam is then directed to a crystal optically dense and contains a high refractive index at a specific angle. 

Its internal reflectance creates evanescent waves that will extend beyond the crystal’s surface straight to the sample in contact with. The evanescent wave will then be attenuated in the infrared spectral region where the sample absorbs energy. Then the attenuated beam will return and exit through the crystal to reach the machine’s detector. 

An interferogram signal is then recorded by the detector, and it will be used to create and generate an infrared spectrum. Most FTIR spectroscopy instruments widely use this sampling method. Its main advantages include minimal penetration of the sample and its accuracy even on thick and difficult samples. 

Attenuance total reflectance can also examine the following hard solids:

  • Plastics
  • Laminates
  • Rubbers
  • Natural powders
  • Coatings
  • Paints 


The transmission technique is one of the easiest methods because you don’t need a separate accessory. You just need to place the sample into the infrared beam, and when the beam passes through it, the energy transmitted is measured, and a spectrum is already generated. This simple sampling method is best for quantitative work, and several standard operating procedures are based on it. 

Specular Reflectance

A surface measurement technique is a specular reflectance, and this sampling method uses the reflective efficiency principle. According to this principle, every sample consists of a refractive index. This index varies with the light frequency to which it’s exposed. 

Specular reflectance measures how much energy is reflected from the sample’s surface instead of measuring the amount of energy passing through the sample. You can measure this by examining the bands of frequency, giving you the qualitative data of the sample absorbency.

Diffuse Reflectance

Diffuse reflectance involves the incident radiation penetrating the sample particles and scattering from them. When the infrared beam focuses on a particulate material, its incident beam interacts with the particle, and radiation reflects off the particle’s topmost surface without penetrating it. Afterwhich, the light undergoes several reflections from the surfaces of the particle without penetration. 

The common applications of diffuse reflectance include solids that can be ground to form a fine powder, such as rigid polymers and tablets. 

FTIR Spectroscopy Instrument and Its Advancements


The FTIR spectrometer provides efficient and advanced sample analysis methods, providing more accurate and precise readings during spectrograph interpretation. Thanks to this innovative machine, scientists and researchers can now separate, analyze, and make comprehensive conclusions on specific samples used in culture, food industry, science, etc. 

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