Fourier Transform InfraRed spectrometer (FT-IR)
Infrared spectroscopy is a fast and easy method for identifying organic substances.
The technique: Infrared light is sent onto or through the sample. The substance is identified by comparing its IR spectrum with spectra from known substances in a library. If the sample contains several different substances, a more advanced analysis has to be carried out. Fourier Transform IR has the advantage that it works well on small samples and that the results are obtained relatively fast. The technique is well suited for the analysis of polymers, textiles, oils, paper, etc.
Several specialised techniques are available:
ATRPotassium bromideMicroscopeOther methods
The instrument: We have a Perkin-Elmer System One-spectrometer, equipped with ATR and microscope.
Key features of the instrument:
Number of spectra in the library | 3000 |
Sample requirements:Amount | > 1 mg |
State | Solid or liquid |
Contact person: Kjell Windsland, phone: +47 98 28 39 41
Further description of the special techniques:
Attenuated Total Reflectance (ATR) is used for surface analysis of soft samples and liquids.
See figures below. The sample is put on top of the blue crystal. The IR beam picks up a signal since it passes a few micron into the sample before it is reflected. It is therefore important to obtain good contact between the crystal and the sample. This can be achieved by pressing the sample down on the crystal as shown in the right hand image. If the substance under study is a liquid, it is simply dropped onto the crystal, thereby obtaining optimal contact.
Light path in the ATR setup.
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Equipment to push the sample onto the crystal.
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Potassium bromide (KBr) does not influence the IR spectrum in the wave number range 4000 til 400 cm-1. This technique can be used when the sample material can be crushed or ground. A couple of milligram of sample is mixed with about 200 mg of KBr powder. The mixture is pressed into a tablet which is then used in the analysis.
Light path with the KBr-technique.
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Sample holder with a KBr-tablet, ready
to be analysed in the sample chamber.
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Microscope: With a microscope one can analyse very small samples, down to 5 µm x 5 µm. Both transmission and reflection techniques can be used.
FT-IR Microscope
Other methods: There are a number of other IR techniques, among others:
- Specular reflectance is used to analyse thin layers on metals.
- Diffuse reflectance is used to analyse powder samples. The powder is put in a separate holder which is especially made for this method.
- By using special cells one can also analyse gases.
- Quantitative analysis is possible, but is more complicated and time-consuming.
