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Vibrational Spectra ( IR Spectra)
IR spectroscopy is concerned with the study of absorption of IR radiation (800nm- 1mm), which causes vibrational transition in the molecule. When a gaseous molecule absorbs IR radiation, it produces transition between the vibrational energy levels. Resultant spectrum is called vibrational spectra. The essential requirement for a molecule to produce IR spectrum is that the dipole moment of the molecule must change during vibration. Thus vibrational spectrum is given by hetero nuclear diatomic molecules. Polyatomic molecules with and without dipole moment also produces IR spectrum. Homo nuclear diatomic molecules such as O2, N2, H2 etc. will not produce IR spectrum, since they have zero dipole moment. But molecules like HCl, HBr, NO2, H2O, CO2, NH3, CH3Cl and SO2 can produce IR spectra and they are IR active molecules. In the case of polyatomic molecules without dipole moment, the exciting radiations can induce an
oscillating dipole moment. Hence they are also IR active.
When a gaseous molecule having dipole moment vibrates, it generates an electric field which can interact with electrical component of IR radiation. During this interaction energy can be emitted or absorbed in the form of radiation of definite frequency.
Instrumentation of IR spectrometer
Theory of IR spectra In order to explain the theory of IR spectra, consider the vibration of hetero nuclear diatomic molecule. It is similar to the vibration of a simple harmonic oscillator.
Vibrational energy of simple harmonic oscillator = Vibrational energy of diatomic molecule
Evib=(v+ 1⁄ 2)hω
Reduced mass (μ) = m1m2/m1+m2
When the molecule is in the vibrational ground level (v =0), E vib = ⁄ hω. This is the lowest vibrational energy level and it is called zero point energy.
Let us consider the vibrational transition from lowest vibrational (v1) to the next higher vibrational energy level (v).
Chromatography
This method is generally used for the seperation of complex mixtures which cannot be seperated by other methods. It is also useful for the seperation and purification of organic compounds when they are available in very smaller quantity.
General principle of chromatography :It is based on the principle of selective distribution of mixture of compounds between two phases, viz stationary phase and mobile phase.
Stationary phase is the fixed phase.
Stationary phase is a solid or a liquid. If the stationary phase is a solid, then the principle adsorption and such type of chromatography is called adsorption chromatography. Example column chromatoraphy.
If the stationary phase is a liquid, then the principle artition and such type of chromatography is called partition chromatography. Example Gas liquid chromatoraphy.
Mobile phase is the moving phase. It can be a liqid or gas. The components to be seperatedis carried by the mobile phase through the stationary phase.
Classification of chromatography based on mechanism of separation,
a) Adsorption chromatography: In this chromatography stationary phase is solid and mobile phase is a liquid or gas. Here separation occurs due to the difference in the adsorption coefficients of the components.
b) Partition chromatography: In this chromatography stationary phase is a liquid supported on inert solid and mobile phase is a liquid or gas. Here separation occurs due to the difference in the partition coefficients of the components.
c) Ion exchange chromatography: In this chromatography stationary phase is an ion exchanger and the separation of the mixture is based on ion exchange principle and applicable for ionic species.
Classification of chromatography based on the mobile phase,
a) Liquid chromatography: If the mobile phase is liquid and the stationary phase is solid, then the chromatography is called LSC (Liquid Solid Chromatography)
If the mobile phase is liquid and the stationary phase is liquid supported on solid, then the chromatography is called LLC (Liquid Liquid Chromatography)
b) Gas chromatography: If the mobile phase is gas and the stationary phase is solid, then the chromatography is called GSC (Gas Solid Chromatography)
If the mobile phase is gas and the stationary phase is liquid, then the chromatography is called GLC (Gas Liquid Chromatography)
c)Column chromatography : In column chromatography stationary phase is held in a narrow tube and is packed with solid adsorbents like Al2O3, silica gel, MgO etc. This can function as the stationary phase.
Thin Layer Chromatography (TLC)
Thin layer chromatography was developed by Izmailov and shraiber. It is better than column chromatography. This method is used for determining the number of components in a mixture. This method will give an idea about the identity of components in the mixture. This will give an idea about the purity of compounds.
Applications: It is used for finding the purity of compounds.
To determine appropriate solvent for column chromatographic separation.
It is used for the identification of a compound.
It is used for monitoring column chromatographic separation.
High Pressure Liquid Chromatography (HPLC)
HPLC is widely used for analytical separation because of its high sensitivity, accurate quantitative determination and its ability to separate non – volatile species.
HPLC Apparatus
i) Solvent delivery system
ii) Sample injection system iii)Chromatographic column iv) Detector
v) Recorder
Applications:
Used in pharmaceutical biological study.
Used in the analysis of water soluble and fat soluble vitamins.
Used in the analysis and separation of amino acids & proteins.
Used in the separation of lipids & steroids.
Gas chromatography (GC) : Gas chromatography is based on the principle of selective distribution components of mixture between two phases, viz stationary phase and mobile phase. In gas chromatography separation occurs between gas mixture and the stationary phase. Mobile phase is a mixture of vaporized sample and inert carrier gas. Usually used carrier gas is nitrogen. Sometimes Ar, He, H2 can also be used as the carrier gas depending on the nature of mixture. Stationary phase may be a solid or liquid. So there are two types of gas chromatography
1) Gas Solid Chromatography (GSC) 2) Gas liquid Chromatography (GLC)
Applications: Used for qualitative analysis , Used to test the purity of compounds, The presence of impurities will be revealed by the appearance of extra peak, Widely used for study of air pollution.