Applications of Fourier Transform Infrared Spectroscopy (FTIR)

What is FTIR?

Fourier Transform Infrared Spectroscopy (FTIR) is a widely used analytical technique that measures the interaction of IR radiation with a sample to provide chemical identification. FTIR is a relatively modern technique, with the first affordable instrument produced in the late 1950s. You are likely to find at least one FTIR instrument in most analytical laboratories.

What are Common Applications of FTIR?

The most popular application is typically still the identification check of a sample of known composition/chemical structure against a known/certified reference standard. FTIR is generally a bulletproof reliable technique for this type of analysis.

Anyone who has studied chemistry will likely remember the tutorials on FTIR where the unique absorption pattern of samples is analysed to identify functional groups and molecular structures by identifying the types of bonds present. I certainly remember having to learn common absorption bands such as those associated with carbonyl compounds (such as carbon dioxide) which is in the range of 1670 to 1780cm^-1. This is an important group not only for characterization of compounds, but to identify interference from atmospheric carbon dioxide in the sample analysis. However, there is much more that can be achieved from FTIR than a simple identification check depending on your area of research/interest.

FTIR in Various Industries

I have listed some common and some not so common industries and applications below.

• Pharmaceutical/Chemical Industry – Identification check of chemicals or pharmaceuticals against a known reference standard
• Materials Science – Researchers can analyse different types of known/unknown polymers, coatings or other materials to assess their composition. This can be done against a library of known polymers or other compounds and aids in understanding the structure, behaviour, performance and potential applications of such materials
• Food and Beverage Analysis – The food industry uses FTIR to assess nutritional content, detect adulterants, and ensure product quality and safety
• Gas analysis – Using multiple sizes of specialized gas cells to analyses samples in a gaseous form be it standard identification checks or analysis of samples from processes such as anaerobic digestion
• Contaminant analysis – This could relate to environmental samples to test for things like air and water quality. The use of an FTIR microscope has been an advantage in this area when examining microplastic contamination
• Quantitation – Quantitation by FTIR using a calibration curve is possible. Although not as common as with other techniques such as UV or chromatography, it can be effective if your sample does not produce a good chromophore but has characteristics which make it better suited to analysis by FTIR
• Forensics – FTIR assists forensic experts in analysing trace evidence, identifying unknown substances, and supporting criminal investigations
• Continuous or Time Course measurement – allows spectra to be collected to monitor changes in sample composition over time such as during an ongoing reaction process (e.g. polymerization reactions)
• Art Conservation – The composition and manufacture of paints and other materials used in art and similar areas has changed over time. FTIR aids in analysing pigments, dyes, and binding materials used in artworks. Which contributes to effective dating along with restoration and preservation efforts

Typical application – Identification testing using a known reference standard

Background

As mentioned in my introduction above, this is the most common application that is used for the FTIR technique. This applies most widely to pharma and biopharma companies. Any company in this space will have to test their products (including raw materials, intermediates and final products) to generally accepted official monographs (such as USP/EP) or specifically filed analytical test methods.

FTIR application

Traditionally, the transmission measurement of solid samples by FTIR involves mixing a small quantity of your powder sample with an inert substance like potassium bromide (KBr) and compressing it with a hydraulic press to form a thin disc. The quantities of sample and KBr are typically weighed to produce a disc of a particular concentration (e.g. 1% sample in KBr). This allows for consistent discs and spectra to be produced, which is important for comparison in spectral libraries if using your own measured standard spectra to perform a pass/fail judgement. Any significant mismatch in transmission between your sample and standard spectrum could result in a failure being noted. For liquid samples, the analysis is performed by placing a few drops of sample on a solid KBr plate and clamping a second KBr plate on top. The liquid sample can then be analysed by placing the sample holder into the FTIR instrument. A standard can be analysed in the same manner to allow for comparison

What is ATR?

In more recent years, the advancement of FTIR has produced a related technique called ATR-IR. ATR is an accessory that can be inserted into the traditional sample compartment to replace the disc holder. It does not require the use of KBr or the preparation of discs. Instead, the sample is placed onto a small crystal with pressure applied through an arm on top of the accessory. This has advantages in terms of speeding up the process of sample analysis as there is no time-consuming disc preparation and cleaning of the crystal between samples is quick and easy. The trade-off is that because the ATR crystal is small (much smaller than the size of a standard KBr disc), the amount of energy that travels through the sample is reduced by around 80-90%. It doesn’t suit all applications but is ideally suited to identification measurements where labs will typically be analysing a large number of samples in one session.

Areas of growing Interest in FTIR:

1. Plastics/microplastics

Background

In recent years, there has been increased focus on reducing single-use plastics. This is part of wider measures to tackle climate change and our overall impact on the environment. Single-use plastics have contributed to significant levels of pollution worldwide. This has caused unsightly build-up in landfills and damage to rivers, lakes, and oceans. Discarded plastic packaging has caused issues for animals, such as entanglement or choking if swallowed. This can be painful and impossible to undo without human intervention.

The knock-on effects of plastic pollution can now be seen in the volume of microplastics detected in many animals, particularly aquatic ones. This contamination carries over into humans as the food chain has become contaminated. Air-borne microplastic particles are also having an impact. It has been estimated that every year, an average human consumes as much plastic as would be contained in 50 plastic shopping bags.

As a result, research into microplastics and their effect on animals and humans has increased in recent years. Microplastic particles have now been detected in the lungs and even within human cells. This has caused increasing concern among the scientific and healthcare community about the long-term effects on our bodies. These include increased cancer risk, lung problems such as COPD and Asthma, and damage to other major organs.

FTIR application – Plastics

Analysis of plastics (including microplastics) is possible using FTIR. This can be enhanced using an FTIR microscope system. Plastics consist of polymers with unique chemical structures. These can be characterised and identified according to their absorption bands. The FTIR microscope can be used to view much smaller areas of the samples. This allows for detailed analysis to identify imperfections and microscopic contaminants within the sample. FTIR also allows the use of spectral libraries to identify samples of unknown content against known standards. The libraries are extensive and varied. They include standard polymers, polymer mixes, and thermally damaged plastics. This makes FTIR a very helpful tool when researching or analysing any type of plastic samples.

2. Anaerobic Digestion

Background

Anaerobic digestion involves sealing manure and other biomass feedstocks into an air-free container. Consequently, this allows bacteria to break them down. The process produces biogas and a digestate by-product. Additionally, you can add other biomass feedstocks. These include domestic food waste, waste from food processing, silage, and crops grown specifically for anaerobic digestion.

Biogas mainly consists of methane and smaller amounts of carbon dioxide. Furthermore, it contains trace amounts of nitrogen, hydrogen, ammonia, and hydrogen sulphide. The methane content varies between about 50% and 80%. Meanwhile, the carbon dioxide content ranges from 20% to 50%. You can use biogas to generate electricity or heat. Refining the process can maximise the methane content. Moreover, further extraction and purification can produce biomethane with a methane content of 99%. This is suitable for addition to the natural gas grid. You can scale the process to suit the needs and location of the facility. For example, this includes farms, food processing plants, or dedicated plants generating biogas and electricity for the national grid. Finally, the digestate by-product, rich in phosphorus, makes an excellent enhanced fertiliser.

FTIR Application – Biogas

You can analyse samples of biogas from the process using FTIR to determine the contents of the mixture and assess the efficiency of the process. You can also potentially use it to monitor the process on an ongoing basis with a flow-through cell setup. Various sizes of gas cells are available, from short path cells of 50mm up to large, long path cells of 30m, to suit all applications. The benefit of FTIR lies in its simplicity, allowing for quick analysis turnaround.

Shimadzu and Mason Technology – Excellence in Science

Shimadzu, available exclusively from Mason Technology, offers a comprehensive range of FTIR instruments, renowned for their precision, reliability, and innovative technology, catering to diverse applications in environmental, pharmaceutical, and industrial testing.

Highlights from their FTIR Instrument Range 

• IRXRoss Spectrophotometer: creates a new concept for infrared spectroscopy. It offers the optimal solution for a new era with a range of diverse application requirements.
• IRSpirit-X Spectrophotometer: Extremely compact instruments that can still be used with standard accessories from Shimadzu and other manufacturers. IRSpirit instruments come with IR Pilot software, which offers 23 application programs without the need for parameter setup.
• Full range of Shimadzu FTIR Instruments