Fourier Transform Infrared Spectroscopy (FTIR)

Fourier transform infrared radiation spectroscopy can be used to study both organic and inorganic materials.

To the left: close up of an instrument. To the right: a woman looking at a computer screen.

To the left: the microscope can be used in reflection and in transmission mode. Coatings are measured using the reflection mode, while thin samples in transmission mode, preserving the structure. To the right: The IR spectrum contains information on the molecular structure of the sample and allows in many cases the identification the material. Photos: UiO.

The interaction of infrared radiation (IR) with the matter causes absorption of wavelengths characteristic for certain moieties. The absorption is plotted against the energy of the infrared radiation in the resulting spectrum. Interpretation of the spectrum allows both the identification of chemical groups (carbonate, sulphate, organic acids etc.), and of compounds by comparison with a database.

However, if compounds are chemically similar, it could be difficult to distinguish them only through infrared radiation. Therefore, infrared radiation spectroscopy is often coupled to other complementary techniques (e.g. Raman spectroscopy, XRD, LC/MS or GC/MS). Infrared radiation spectroscopy cannot detect single chemical elements directly.

Close up of a microscope.
Left: The microscope can be used in reflection and in transmission mode. Here we see the micro ATR used to examine cross-sections. Right: In the standard ATR mode, a small sample is placed on the little crystal window in the centre of the metal plate, and pressed. Photos: UiO.

Infrared radiation can be divided into three regions, depending of the wavelength. Each region requires a separate detector:

  • Far-infrared region (20-400 cm1): compounds that are not detectable in the mid-infrared region exhibit signals in the far-infrared region, among which oxides and sulphides being the most common examples
  • Mid-infrared region (400-4000 cm1): the region, which is commonly used to identify organic and inorganic compounds
  • Near-infrared region (4000-40 000 cm1): this region is mostly used to study carbohydrates, e.g. wood and binding media

FTIR can be used to study both organic and inorganic materials

Typical examples of organic materials in the cultural heritage field are:

  • binding media (oils, proteins, carbohydrates)
  • varnishes (resins)
  • supports (paper, canvas, wood)
  • textile fibres
  • food residuals (butter, oil, honey, wine, etc.)
  • dyes
  • polymers (conservation treatments, plastics, etc.)
  • wood
  • leather

Examples of inorganic materials include:

  • pigments
  • minerals
  • glass
  • ceramics
  • mortars
  • plasters
  • corrosion products (e.g on metals, glass or other substrates)

Different configurations FTIR can work with

The FTIR-instrument available at SciCult-KHM is equipped to work in different configurations, depending from type of sample and research question:

  1. Attenuated total reflectance (ATR): this device – the most frequently used – allows the analysis of a large range of samples, from liquids to solids. The advantage is of a simple and quick measurement, but the structure of the sample is compromised. 
  2. Transmission mode that allows bulk analysis of solid and liquid samples, both qualitatively and quantitatively. Most accurate way of measuring.
  3. IR microscopy used for high-resolution qualitative analysis of microsamples through transmission, reflectance, and ATR. The microscope allows automatic point analysis and area mapping. Here it is possible to keep the structure of the sample to a certain degree. Cross-sections can be investigated.
Published Sep. 21, 2022 10:34 AM - Last modified Sep. 21, 2022 1:28 PM
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