The Principle of FTIR

FTIR is a type of spectroscopy that used infrared light. The results of FTIR sample is a spectrum that is like a molecular fingerprint. The spectrum depicts the transmission and absorbance of light for all the infrared wavelengths.

The Process

A sample is placed into an FTIR spectrometer. The light source will pass different wavelengths of light through the sample. On the other side of the sample is a detector which detects the light that is transmitted through the sample.

Algorithm

Fourier algorithms are used to transform the absorbance and transmittance information into a spectrum. These algorithms are complicated and a computer program is used for the calculations.

Spectrum

Each peak on the infrared spectrum, will correspond to a chemical bond. By comparing the percent transmittance for each wavelength and comparing them with known chemical transmittance it is possible to determine the structure of unknown compounds.

Background

Normally a background spectrum is collected along with the sample spectrum. This will remove instrument characteristics from the sample spectrum. Think of it as zeroing the machine before running a sample.

References

• ThermoNicolet Corporation: Introduction to Fourier Transform Infrared Spectrometry
• Daham: Principles of Fourier Transfer Infrared Spectroscopy