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Fourier Transform Infrared Spectrometer (FTIR)

Fourier Transform Infrared Spectrometer (FTIR) 


Molecules are formed by chemical bonding of atom which FT/IR determine molecular structure vibration and rotational energy OR Identification of chemical function groups.

Fourier Transform Infrared Spectrometer
Image Source-Google | Image by -QC/QA Methodology
When IR beam goes to beam splitter. It is divided in two directions; one IR beam goes to movable mirror and other goes to stationary mirror. Movable mirror move around 21cm. Both IR beam return to beamsplitter thus it have different wavelength, these IR beam goes to detector through sample and detector send electronic signal to computer.

Calibration of FTIR:

Calibration done by the using calibrated polystyrene film which have 36 ┬Ám thickness and check the below parameter.
  1. Resolution performance
  2. Verification of wave number
Resolution performance:
Step 1= Record the spectrum of a secondary polystyrene film of 36 micro meter thickness the film has a reference number and a validity certificate traceable.
Step 2= Check the percent absorbance at the absorption minimum at 2870.0 cm-1 and absorption maximum at 2849.5 cm-1. The difference percent absorbance between the two should be greater than 0.33 The difference between the percent absorbance at the absorption minimum at 1589.0 cm-1 and the absorption maximum at 1583.0 cm-1 should be greater than 0.08. 
Maximum      : at about 2849.5 cm-1
Minimum       : at about 2870 cm-1
Transmittance  : Grater than 6% for prism instrument
Transmittance  : Grater than 18% for grating instrument and
Maximum      : at about 1583 cm-1
Minimum       : at about 1589 cm-1
Transmittance  : Grater than 6% for prism instrument

Transmittance  : Grater than 12% for grating instrument 
Verification of wave number scale: 
Step 1= The wave number scale verified by using traceable serialized secondary polystyrene standard of 36 micrometer thickness which has transmittance minimum absorption Maximum at the wave number in cm-1 as shown below
Step 2= Transmission minim and acceptable tolerances of polystyrene film.
3060.0 (±1.0) cm-1
2849.5 (±1.0) cm-1
1942.9 (±1.0) cm-1
1601.2 (±1.0) cm-1
1583.0 (±1.0) cm-1
1154.5 (±1.0) cm-1
1028.3 (±1.0) cm-1
The frequency for calibration as every three month.

Additional information about FTIR

Question: Why using KBr and NaCl for blank.?
Answer: Its nature does not interfere with sample.It has know peak.Before testing it must be heat at 80°C for 3 hrs. because released moisture.
Question: Why using polystyrene film for calibration of FTIR.?
Answer: Because it shows an accurate result any condition & any temperature.
Question: What mean by Fourier transform.?
Answer: Fourier transform of the time domain transitional signal yield the corresponding frequency. Spectrum this is high resolution technique yielding M/Z ratio to about one thousand of Dalton.
Question: What is the purpose of FTIR?

Answer: Fourier Transform Infrared Spectroscopy also known as FTIR Spectroscopy, It is an analytical technique used to identify organic, polymeric, and, in some cases, inorganic materials. FTIR infrared light to scan of test samples and show chemical properties.
Question:What is in the fingerprint region?
Answer:The region to the right-hand side of the diagram (from about 1500 to 500 cm-1) usually contains a very complicated series of absorption. These are mainly due to all manner of bending vibrations within the molecule. This is called the fingerprint region.
Question:What is the functional group region IR?
Answer: The functional group region runs from 4000 cm-1 to 1450 cm-1, and the fingerprint region from 1450 cm-1 to 500 cm-1. ... The functional group region contains relatively few peaks. These are typically associated with the stretching vibrations of functional groups.


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