Overview of FT-IR Analysis Technology
FT-IR analysis, or Fourier Transform Infrared Spectroscopy, is an analytical chemistry technique used to obtain the infrared spectrum of a substance. This technique is primarily used to identify chemical substances or detect the presence of specific compounds.
FT-IR analysis is based on the ability of substance molecules to absorb infrared light at specific wavelengths. Different chemical bonds and functional groups will absorb infrared light within a specific infrared wavelength range, producing characteristic absorption peaks. By measuring these absorption peaks, the chemical composition of the sample can be determined.
Analysis Workflow
1. Sample Preparation
For the preparation of solid samples for FTIR spectroscopy, KBr is used. About 2 mg of the sample and 200 mg of KBr are dried and ground. The particle size should be uniform, less than 2 um. The mixture is then compressed to form a transparent granule that can be measured directly. For high boiling point liquids or viscous solutions, they can be added between two NaCl granules. The sample is then tilted and fixed in the sample pool for measurement. For volatile liquid samples, dissolve them in CS2 or CCl4 to form a 10% solution. The solution is then injected into the liquid pool for measurement. Gas samples need to be measured in a gas chamber with two KBr windows on each side. The gas chamber should be evacuated first. The sample can then be introduced into the gas chamber for measurement.
2. Obtaining Background Spectrum by Collection of Interferograms and Conversion to Frequency Data Through Fourier Inverse Transform
The reason we obtain a background spectrum is that the solvent where we place our sample will contain trace dissolved gases and solvent molecules, which will provide information not belonging to our sample. The background spectrum will contain information about the types of gases and solvent molecules, which can then be subtracted from our sample spectrum to obtain only information about the sample.
3. Collect the Single-Beam Spectrum of the Sample
Next, we collect the single-beam spectrum of the sample, which contains the absorption bands of the sample as well as the background (gas or solvent).
4. Calculate the Spectrum of the Sample
The ratio of single beam sample spectrum to single beam background spectrum gives the spectrum of the sample.
5. Data Analysis
Data analysis is completed by assigning the absorption bands observed in the sample spectrum to the appropriate normal vibrational modes in the molecule.
Applications
FTIR spectra are widely used in organic synthesis, polymer science, petrochemicals, pharmaceutical industry, and food analysis. In addition, since FTIR spectrometers can be used in conjunction with chromatographs, they can be used to study the mechanism of chemical reactions and the detection of unstable substances.
Advantages
The main advantages of FT-IR analysis include fast results, little or no sample preparation, non-destructive testing, and detailed information about molecular structure.
Limitations
Although FT-IR is a powerful analytical tool, it cannot provide information about the mass of atoms or the molecular weight in the sample, and it is difficult to analyze complex mixtures containing similar functional groups.
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