Fourier Transform Infrared Spectroscopy (FTIR)

 

Fourier Transform Infrared Spectroscopy (FTIR)

Fourier Transform Infrared Spectroscopy (FTIR)

¨  FTIR spectroscopy is an analytical technique, which is used for identification of Organic, Polymeric, Inorganic compounds in Pharmaceutical industry, Petrochemical engineering, And Food industries.

¨  FTIR uses Infrared light  to scan test sample and observe chemical properties. It works on the fingerprint of molecules, which is a great tool for us in chemical identification.

¨  The range of infrared region is 12800 ~ 10 cm^-1 near-infrared region (12800 ~ 4000 cm^-1), mid-infrared region (4000 ~ 200 cm^-1) and far-infrared region (50 ~ 1000 cm^-1).

¨  FTIR Spectrophotometers are 3^rd generation Infrared Spectrophotometers having following advantages.

¨  Higher signal to noise ratio than other spectrophotometers.

¨  Very short scanning time and wide scan range.

¨  Wave number accuracy is very high.

¨  Resolution capability is very high.

¨  Stray light interference is minimum.

Instrumentation

¨  Source

¨  Interferometer

¨  Sample Compartment

¨  Amplifier

¨  Detector

¨  Computer System

Michelson Interferometer

¨  Michelson interferometer is the most important part of the FTIR.

¨  It consist of two mirrors lined perpendicular and a beam splitter.

¨  One of the mirrors is stationary and other one is moveable.

¨  The beam splitter is lined in such a way that when light is passing through it, it transmit half of the light and half of the light is reflects.

¨  Upon reflection the beams recombined at the beam splitter.

        

 

Interferogram

¨  Spectrum or signal format that is obtained through FTIR spectroscopy is termed as interferogram.

Functional Group Region

¨  Functional group region lies from 4000cm-1 to 1450cm-1, it contains few peaks.

Finger Print Region

¨  Finger print region lies from 1450cm-1 to 500cm-1, it usually contains a bunch of peaks.

How FTIR Works

¨  FTIR is based on the Michelson interferometer Experimental setup as shown in previous slide

¨  The interferometer consist of Source, beam splitter, fixed mirror, movable mirror(translates back and forth very precisely), and output.

¨  The beam splitter is made of special material which transmits half radiation and reflects half radiation.

¨  The radiation from the source strikes beam splitter which is divided into two beams, one beam transmits to fixed mirror and 2^nd beam reflects back to beam splitter.

¨  Again half radiation transmits and half reflects back to beam splitter.

¨  This transmission and reflection results in one beam passes to output (detector) and the other beam back to the source.

Principle of FTIR

¨  The basic principle of FTIR is to identify the functional group by providing or striking the material with some energy packets (in the form of IR light/Radiation).

¨  The functional group in a material attached with each other with specific bonds. And these bonds will produce some stretching, wagging and vibrational movement when struck by IR source.

¨  Now when IR radiation passes through a molecule, some radiation will be absorbed and some radiation passes through. The absorbed radiation is converted into that movement   ( Rotational, Vibrational) by sample molecule, representing the molecular fingerprint (Functional Group) of sample.

¨  The resulting signal on detector produce a spectrum which is shown on our monitor of computer attached to FTIR.

Applications

¨  Analysis of different materials in food industry.

¨  Identification and analysis of materials in Pharmaceutical industry.

¨  Analysis of environmental pollutants.

¨  Useful in carrying out different identifications in forensic laboratories.

¨  Analysis of polymers can be carried out.

¨  Geological studies can also be performed with the help FTIR spectroscopy.