IR SPECTROSCOPY -IMA - B.PHARM

 

Basic’s and Principal of the IR spectroscopy :-

In, IR spectroscopy infrared radiation are used. Infrared radiation are classified into three types Accordingly to they wave length.

•  Near IR :- 0.78 – 2.6μ
• Mild IR   :– 2.5 – 50 μ
•  Far IR   :– 50- 200μ

Mild IR are widely used in pharmaceutical industry.

Main used of IR spectroscopy is to determine functional group of compound and study of structure of nee compound.

Principal

IR spectroscopy are work on principal of absorption. In IR spectroscopy when ir radiation we give any compound it is excited and show vibration.

Applied IR frequency  should be equal to the natural frequency of radiation. Otherwise compound do not give IR peak.

Compound have must be required dipole movement for perfomaning IR spectroscopy.

In any IR spectra there are two important region :-

1. Finger print region

2. Functional group region

• Type of vibration

When we applied IR radiation any compound are absorbed it is saw a vibration.

Compound to compound it is different.

There are mainly two types of vibration

1. Stretching

2. Bending

1. Stretching vibration :– It is type of vibration in which bond angle is constant But bond length is increase or decrease.

It has sub division into two types

i. Symmetrical stretching :-

Bond length is increase or decrease.

But bond angle is constant.

Here’s both bond length is increase or decrease.

ii. Asymmetrical stretching

In this Types of stretching in compound one bond length is increase and other must be decrease.

2 Bending vibration

In this Types bond length is constant but bond angle will be change. Also seen plane movement will be change.

It is sub division into four types

1. Scissoring:– In this type of bond angle is decrease.

2. Rocking :- In this type of vibration bond angle is constant.

3. Wagging :- In this type of Bond angle is constant. But movement will be one plane to another plane.

4. Twisting :– In this type of vibration one bond is one plane and other bond is another plane. In this type bond angle is decrease.

INSTRUMENTATION OF IR SPECTROSCOPY

 

There are mainly five part of IR spectroscopy which are as follows

1. Radiation source
2. Sampling
3. Monochromator
4.  Detector
5. Recorder

1. Radiation source :– There are mainly three types of radiation source are used.

A. Globar source :- It is consists of silicon carbide rod. When heating at 1300c- 1700c. It is produced IR radiation.

B. Nernst glower :- IT is consists of zirconium oxide, chromium oxide and yetrium oxide. It is produced IR radiation when heating at 1000-1800c.

C. Incandescent lamp :- it is consistent of nichrome coil in a glass tube. When it is heating at 1100c.

2. Sampling technique :-

There are mainly two types of sampling technique in IR

• 1. solid sampling technique
• 2. Liquid sampling technique

    1.solid sampling technique

A. pelletization :- In this technique we are using diluent like NACL or KCL which are IR inactive compound. We mixed with NACL and sample and mix by motra and piston. After it is compressed it and prepare pellets. This pellets we put in sample holder.

B. Muling :- the sample can be mixed with Nujol ( mineral oil) and is applied on a liquid sample cell.

     2. Liquid sampling :-

Sample can be held using a liquid sample cell made of alkali halide.

Aqueous solvent cann’t be used as they will dissolve alkali halide. Only organic solvent like chloroform is used.

3. Monochromator :- filter made up of lithium flouride or prisms made of potassium bromide, like alkali metal halide.

4. Detector :- To measure the intensity of unabsorbed IR,we used different type of detector like,

1. Thermocouple :– In this detector we are detected potential different between two junction.
2. Bolometers :–  Thin metal conductor. This detector work on sample principal that increase in temp. When IR radiation come. So, ultamitely increase resistance and current flow is change.
3.  Thermistor :- fused metal oxide mixture increasing temp. Decrease resistance by 5% at 1c.­

5. Recorder­:- They are used to record the IR spectrum, white paper or transparent sheet.

Reference for the analysis of book third edition Dr. S. ravi sankar.