1. Infra-red spectrophotometer

2. What is Infrared (IR) spectrophotometer?
Infrared Spectrophotometry is designed to identify or determine the sample by measuring absorption of infrared radiation of wavenumbers.
This method uses the property that the infrared absorption spectrum of a substance is characteristic of its chemical structure.
For a given sample which may be solid, liquid, or gaseous, the method or technique of infrared spectroscopy uses spectrophotometer to produce an infrared spectrum.
A basic IR spectrum is essentially a graph of infrared light absorbance (or transmittance) on the vertical axis vs. frequency or wavelength on the horizontal axis.

3. Example of IR Spectrum graph

4. Operating Principle:
Molecule are made up of atoms linked by chemical bonds. The movement of atoms and the chemical bonds like spring and ball (vibration). This characteristic vibration are called Natural frequency of vibration.
When energy in the form of IR radiation is applied then it causes the vibration between the atoms of the molecules and when applied IR frequency equal to natural frequency of vibration, then absorption of IR radiation takes place and a peak is observed.
Different functional groups absorb characteristic frequencies of IR radiation. Hence gives the characteristic peak value. Therefore, IR spectrum of a chemical substance is a finger print of a molecule for its identification.

5. Criteria for a compound to absorb IR radiation:
1. Correct wavelength of radiation
A molecule to absorb IR radiation, the natural frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation.
2. Change in dipole moment
A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole. A molecule is said to have an electric dipole when there is a slight positive and a slight negative charge on its component of atoms.

6. How the Infrared Spectrophotometer works:

7. Types of Measuring Devices

8. Instruments for measuring infrared absorption all require a source of continuous infrared radiation and a sensitive infrared transducer, or detector. 
Infrared sources consist of an inert solid that is electrically heated to a temperature between 1,500 and 2,200 K. The heated material will then emit infra red radiation.

9. Nernst Glower 
Is constructed of rare earth oxides in the form of a hollow cylinder.
Platinum leads at the ends of the cylinder permit the passage of electricity.
Fragile.
Have a large negative temperature coefficient of electrical resistance.
Must be preheated to be conductive. 

10. Globar Source
Is a rod of silicon carbide which is electrically heated to about 1,500 K.
Water cooling of the electrical contacts is needed to prevent arcing.
The spectral output is comparable with the Nernst glower, except at short wavelengths (less than 5 mm) where it's output becomes larger. 

11. Carbon Dioxide Laser Is used as an infrared source that
- monitor certain atmospheric pollutants
- determine absorbing species in aqueous
solutions. 
It is tuneable.

12. Detectors Can be classified into three categories ： thermal detectors
pyroelectric detectors
photoconducting detectors

13. Thermal Detectors Can be used over a wide range of wavelengths.
Operate at room temperature.
Disadvantages :
- slow response time
- lower sensitivity

14. Pyroelectric Detectors
Consists of a pyroelectric material.
Triglycine sulphate is the most common material for this detectors.
Depends on the rate of change of the detector temperature rather than on the temperature itself.
Operate with a much faster response time.

15. Photoconducting Detectors
The most sensitive detectors.
Rely on interactions between photons and a semiconductor.
Consists of a thin film of a semiconductor material (e.g lead sulphide, mercury cadmium telluride or indium antimonide) deposited on a nonconducting glass surface and sealed into an evacuated envelope to protect the semiconductor from the atmosphere.

16. The lead sulphide detector is used for the near-infrared region of the spectrum. For mid- and far-infrared radiation the mercury cadmium telluride detector is used. It must be cooled with liquid nitrogen to minimize disturbances. 

17. Advantages
Not causing any damage , it is harmless and will not damage the environment or the area being viewed.
Sample being viewed do not need any special preparation, the readings can be taken without doing anything special to the subject at hand.
Almost universal. Many molecules have strong absorbances in mid-infrared. ( many types of samples can have their infrared spectra measured.)
Informative. The peak positions gives the structures of the molecules in a sample.
Inexpensive
Relatively fast and easy.

18. Disadvantage
Poor sensitivity to molecular units with small oscillatory dipoles during a vibrational transition and difficult to detect minor component of samples.
Does not provide information of the relative positions of different functional groups on a molecule
Spectroscopy is mixtures. The more complex the composition of a sample, the more difficult t is to determine what peaks are from what molecules.
It is water. Liquid is broad and has intense peaks can mask the spectra of solute in liquid water needs to be present in a concentration greater than 0.1% to be seen.

19. Test Related
The experiment involve using of infrared spectrophotometer are widely used in chemical both organic and inorganic chemistry, in research and industry.

20. Sample Preparation
IR spectroscopy can be done by any pure sample regardless of the physical state.
Solid, Liquid or Gas
Important to note that spectra obtained from different sample preparation methods will look different.

21. There are two common methods of sample preparation of pure solid:
KBr Pellet Method
Nujol Mull Method
There are one common method of sample preparation of pure liquid:
Solution Cell Method

22. KBr Pellet Method (Solid)
g of solid sample and 0.1 g of Potassium Bromide (KBr) are mixed in the mortar.
2.The contents in the mortar are ground well with a pestle into a fine mixture around 2 minutes.
3. A small amount of the finely crushed mixture is put into the open chamber. The amount of mixture should be just enough to cover the bottom surface of the chamber
4. The lid is put on the chamber that containing the finely crushed mixture and 3 piece metal set are put inside the Qwik Handi-Press, it is pressed hard and then the press is released.

23. 5. The 3 piece metals are carefully took out from the Qwik Handi-Press and the Pellet formed within the middle metal piece of the 3 piece metal set is examined. The Pellet should be clear and free from cracks. The procedures are repeated if the Pellet is opaque or has cracks.
The middle metal piece that has the clear and uncracked pellet is took and screwed to the pellet holder.

24. Nujol Mull Method
g of solid sample are added onto a mortar and pestle, a small drop of Nujol, mineral oil is added and the sample powder is mixed in the liquid paraffin.
2. The well-mixed paste is applied to a KBr plate and sandwiched it under another plate, the two plates are gently circular and back-and-forth rubbed to ensure the mixture are evenly distributed between two plate

25. Solution Cell Method (Liquid)
1. The NaCl plates are took out from the oven.
2. The NaCl plates are cleaned thoroughly with chloroform and dried with tissue.
3. A dropper is used to drip one drop of sample onto a NaCl plate.

26. 4. It is sandwiched with another NaCl plate at an angle
4. It is sandwiched with another NaCl plate at an angle. The sample should spread out to cover the entire plate. (If it does not cover well, try twisting the top plate to spread the sample, or add a drop or two more sample. Ensure there are no air bubbles.)
5. The NaCl plates are placed into a sample holder. The 3 screw are tighten in an alternate fashion do not drill in a sample screw before moving on with the next one.

27. Thank you