Presented by:

AISWARYA.A.T,I M.Pharm.,Dept. of Pharmacy Practice,Grace college of pharmacy.

FTIR

A spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, 5 microns to 20 microns.

FTIR (Fourier Transform Infra Red) spectrometer obtains an infrared spectra by first collecting an interferogram of a sample signal using an interferometer, then performs a Fourier Transform on the interferogram to obtain the spectrum.

FTIR

An interferometer is an instrument that uses the technique of superimposing (interfering) two or more waves, to detect differences between them.

The FTIR spectrometer uses

To separate IR light, a grating is used.

Grating

Light source

Detector

Sample

Slit

To select the specified IR light, A slit is used.

Dispersion Spectrometer

In order to measure an IR spectrum, the dispersion Spectrometer takes several minutes.

Also the detector receives only a few % of the energy of original light source.

Fixed CCM

B.S.

Moving CCM

IR Light source

Sample

Detector

An interferogram is first made by the interferometer using IR light.

The interferogram is calculated and transformed into a spectrum using a Fourier Transform (FT).

FTIR

In order to measure an IR spectrum,FTIR takes only a few seconds.

Moreover, the detector receives up to 50% of the energy of original light source (larger than D.S)

Comparison B/W Dispersion Spectrometer & FTIR

COMPONENTS OF FTIR

IR Radiation sourceBeam SplitterFixed mirrorMoving mirrorCollimating mirrorsSample holderHelium Neon laserDetector

FTIR - WORKING

Interferometer

He-Ne gas laser

Fixed mirror

Movable mirror

Sample chamber

Light

source

(ceramic)

Detector

Beam splitter

Better sensitivity and brightnessHigh wavenumber accuracy Enhanced frequency Resolution Wavenumber range flexibility less time consuming Datas can be stored & reanalysed

FTIR – ADVANTAGES & DISADVANTAGES

More expensiveRequire precision for mirror movementDetection of compound is influenced by watervapour, pathlength & chemical interference

Fellgett's (multiplex) Advantage

FT-IR collects all resolution elements with a complete scan of the interferometer. Successive scans of the FT-IR instrument are coded and averaged to enhance the signal-to-noise of the spectrum.

Theoretically, an infinitely long scan would average out all the noise in the baseline.

The dispersive instrument collects data one wavelength at a time and collects only a single spectrum. There is no good method for increasing the signal-to-noise of the dispersive spectrum.

Jacquinot Advantage

FT-IR uses a combination of circular apertures and interferometer travel to define resolution. To improve signal-to-noise, one simply collects more scans.

More energy is available for the normal infrared scan and various accessories can be used to solve various sample handling problems.

The dispersive instrument uses a rectangular slit to control resolution and cannot increase the signal-to-noise for high resolution scans. Accessory use is limited for a dispersive instrument.

Connes Advantage

An FT-IR uses a He-Ne laser as an internal wavelength standard. The infrared wavelengths are calculated using the laser wavelength, itself a very precise and repeatable 'standard'.

Wavelength assignment for the FT-IR spectrum is very repeatable and reproducible and data can be compared to digital libraries for identification purposes.

Opaque or cloudy samples

High resolution experiments (as high as 0.001 cm-1 resolution)

Trace analysis of raw materials or finished products

Depth profiling and microscopic mapping of samples

Kinetics reactions on the microsecond time-scale

Analysis of chromatographic and thermogravimetric sample

fractions

APPLICATIONS