Saturday, 15 December 2012

WHAT IS FTIR | FOURIER TRANSFORM INFRARED SPECTROSCOPY


What Is FTIR? 

What is FTIR? A description about "what is FTIR" and a brief introduction of FTIR.

FTIR spectroscopy is also known as Fourier Transform InfraRed spectroscopy, this method of infrared spectroscopy is a widely used method. In this infrared spectroscopy, Infra Red (IR) radiation is passed through a sample. Some of the infrared radiation is absorbed by the sample and some of it are transmitted.
The spectrum which produced, represents the transmission and molecular absorption creating a molecular fingerprint of the sample. This fingerprint region is used for analysis of sample. We know that fingerprint of no two unique molecular structures produce the same infrared spectrum. This property of FTIR is used in spectroscopy for identification of molecule or a compound based on fingerprinting region. This infrared spectrum spectrum represents fingerprint of a sample with different absorption peaks shows different frequencies of vibration between the bond of the atoms in the sample. It is clear that there are different atoms with different combination and hence different fingerprint region and hence unique molecule can be identified based on this property of FTIR.

What is the use of FTIR? 
  • It is used to identify unknown materials. 
  • To determine quality or consistency of materials. 
  • To determine amount of components is a mixture 

Advantages of FTIR 

Some of the advantages of Fourier transform Infrared spectroscopy (FTIR) are as follows: 

  1. Speed- Because all of the frequencies are measured simultaneously, most measurements by FTIR are made in a matter of seconds rather than several minutes. This is sometimes referred to as the Feigett Advantage. 
  2. Sensitivity- Sensitivity is dramatically improved with FTIR for many reasons. The detectors employed are much more sensitive, the optical throughput is much higher referred to as the Jacquinot Advantage. 
  3. Mechanical Simplicity- The moving mirror is the interferometer is the only continuously moving part in the instrument. Thus, there is very little possibility of mechanical breakdown. 
  4. Internally Calibrated- These instruments employ a HeNe laser as an internal wavelength calibration standard referred to as the Connes Advantage. These instruments are self-calibrating and never need to be calibrated by the user. 
Why FTIR?

Fourier Transform Infrared spectrometry was developed in order to overcome the limitation encountered with dispersive instruments. The main difficulty was the slow scanning process. A method for measuring all of the infrared frequencies simultaneously, rather than invividually, was needed. 

A solution was developed which employed a very simple optical device called an interferometer. The interferometer produce produces a unique type of signal which has all on the infrared frequencies "encoded" into it. The signal can be measured very quickly, usually on the order of one second or so. Thus, the time element per sample is reduced to a matter of a few seconds rather than several minutes. 

The original infrared instruments were of the dispersive type. These instruments separated the individual frequencies of energy emitted from the infrared source. This was accomplished by the use of a prism or granting. An infrared prism works exactly the same as a visible prism which separates visible light into its colors (frequencies). A grating is a more modern dispersive element which better separates the frequencies of infrared energy. The detector measures the amount of energy at each frequency which has passed through the sample. This results in a spectrum which is a plot of intensity vs. frequency.


Fourier transform infrared spectroscopy is preferred over dispersive or filter methods of infrared spectral analysis for several reasons: 

• It is a non-destructive technique
• It provides a precise measurement method which requires no external calibration
• It can increase speed, collecting a scan every second
• It can increase sensitivity – one second scans can be co-added together to ratio out random noise
• It has greater optical throughput
• It is mechanically simple with only one moving part

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