FT-IR Spectrometer

In this topic, God willing, we will talk about an infrared Fourier transform spectrometer and everything related to it.

Double beam FT-IR spectrometer

  Most of the infrared spectrometers used are double-  beam spectrometers, because the low infrared energy, the instability of the light source and the unit of measurement, and the need to amplify the resulting weak electrical signals makes a two-beam design necessary for these devices.

 

FT-IR Spectrometer is one of the laboratory equipments that this devices, the source rays are separated into two equal beams by means of a rotating mirror and a light interrupter, where the source rays oscillate alternately between the sample cell and the reference cell.

Finally, the sample beam passes alternately to the radiological analysis unit, as shown in the following figure:

 

Fourier transform infrared FT-IR spectrometer

It is called in English: Fourier Transform Infrared (FT-IR) Spectrometry or Fourier Transform Infrared Spectrometer

Fourier transform infrared spectrometer (FT-IR) is a technology used to obtain infrared spectroscopy for the absorption or emission of a solid, liquid, or gaseous substance.

The Fourier spectrometer simultaneously collects high-resolution spectral data over a wide spectral range. This provides a significant advantage over a scattering spectrometer, which measures intensities over a narrow range of wavelengths simultaneously.

The idea of ​​\u200b\u200bthe work of the FT-IR device

The objective of an absorption spectrometer (FT-IR) is to measure how much light a sample absorbs at each wavelength.

So the most obvious way to do this, dispersion spectroscopy, is to shine a monochromatic beam of light onto a sample, measure the amount of light absorption, and repeat each different wavelength. (eg this is how some UV spectrometers work)

– FT-IR spectroscopy is a less easy way to obtain the same information. Instead of shining a monochromatic beam of light (a beam of only one wavelength) into the sample

– This technique shines a beam containing many frequencies of light simultaneously and measures the amount of absorption that that beam absorbs from the sample.

The packet is modified to contain a different set of frequencies, giving a second data point.

his process is repeated several times.

The computer takes all this data and works backwards to infer what the absorption is at each wavelength.

The beam described above is created by starting with a broadband light source – one that contains the full spectrum of wavelengths to be measured. The lamp lights up in a Michelson interferometer, which is a specific configuration of mirrors, one of which is moved by a motor. As this mirror moves, each wavelength of light in the beam is periodically blocked, transmitted, blocked or transmitted by the interferometer due to wave interference. Different wavelengths are modulated at different rates, so that the beam emerging from the interferometer at each moment has a different spectrum.

Computer processing is required to convert the data (light absorption per mirror position) into the desired result (light absorption per wavelength). The required processing turns out to be a common algorithm called the Fourier transform (hence the name “Fourier transform spectroscopy”). Raw data is sometimes called “interference”.

Features of the FT-IR spectrometer

(1) High analysis speed

The speed advantage was realized because all wavelengths in the spectral domain were examined together and the absorption spectra were displayed in real time.

(2) The absence of cracks and gratings

The absence of a minimum energy of the elements makes it possible that the full energy of the ray that occurs at any point in time will be available. On the other hand, due to the high scanning speed of several spectra added together and the average results of the signal in several fields, it improved its sensitivity.

(3) simultaneous modulation of frequencies

Although a Nicholson interferometer modulates all present frequencies simultaneously, there is no equal to stray light that contributes to a clear spectrum.

(4) calibration of combined wavelengths

The device is based on a He-Ne laser, which is used internally for self-calibration of individual frequencies to have an accuracy of more than (0.01) cm-1. However it is still advisable to run the polystyrene thin film reference spectrum occasionally and compare it to the standard spectrum kept in the reference library at the time of installation.

(5) Absence of moving components

The absence of moving components except for the moving mirror reduces wear and tear.

(6) Absence of clamps and longitudinal slits method

Its absence ensures the coherence of the beams and the absence of discontinuities along the spectral range.

(7) Spectral interference feature

Spectral overlap feature, which helps to compare with standard reference spectra stored in commercial spectrometers or in public libraries.

The high sensitivity inherent in this technology allows efficient use of all device attachments such as reflection diffuser, total reflection attenuator, reflection polisher attachment, gas cells etc. which make FT-IR fast, versatile and reliable for material characterization.

Differences of FT-IR from  Regular IR

– The FT-IR Fourier transform infrared spectrometer differs from the Regular IR in the following:

(1)  Very fast and sensitive

(2)  The power source in the FT-IR spectrometer is LASER Monochromatic source

(3) The FT-IR spectrometer does not contain a monochromator, so the incident beam contains all wavelengths of medium-range infrared rays 5000-400 cm ^-1

(4)  The device is equipped with an Analog to digital converter in order to facilitate its integration with GC-FTIR or HPLC-FTIR chromatographic analyzers.

(5)  The FT-IR spectrometer is characterized by the fact that it analyzes small samples with a faster and more accurate degree than the ordinary device.

(6)  It gives a very high resolution

(7)  It can analyze air pollutants such as carbon monoxide, ethylene oxide, etc.

Shape of the FT-IR Spectrometer

 

The path of the rays in the FT-IR spectrometer

The incident beam is divided into two beams as shown in the following figure:

The first beam has a fixed wavelength and is directed to the fixed mirror.

The second boot has a variable wavelength and is directed to the moving mirror

 

Comparison of FT-IR and Dispersive-IR