How Does FTIR Analysis Work?

How Does FTIR Analysis Work?
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.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.

5 FTIR Analysis Techniques 
 

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

• Attenuated Total Reflectance – ATR spectroscopy only requires that the sample comes into contact with the ATR crystal.
• Specular Reflectance – SR typically occurs with glossy samples, such as glass and crystal.
• Reflection-Absorption – RA works with thin samples such as residues and paints
• Transmission – TR passes IR (radiation) through gas, liquid or solid samples and measures how well the sample absorbs that infrared radiation.
• Photoacoustic – PAS can be difficult, but not impossible. Infrared absorptions are converted to heat inside the sample, creating the photoacoustic signal.

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: 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.