Raman Spectroscopy.pptx

Raman Spectroscopy

1. Presented by- Name- Jubair Sikdar Roll no-04 M. Pharm 1 st semester Department of Pharmaceutical Chemistry RAMAN SPECTROSCOPY NETES Institute of Pharmaceutical Sciences, Mirza

2. CONTENTS INTRODUCTION PRINCIPLE INSTRUMENTATION APPLICATION

3. INTRODUCATION Raman spectroscopy is a technique for studying molecular vibrations by light scattering. Raman spectroscopy was discovered by C. V. Raman in 1928. Raman spectroscopy deals with the scattering of light. It is a spectroscopic technique used to observe vibration , rotational and other low-frequency modes in a system . Raman spectroscopy is commonly used in chemistry to provide a fingerprint by which molecules can be identified .

4. PRINCIPLE When radiation from a source is passed through a sample, some of the radiation is scat t ered by the molecules present. The beam of radiation is merely dispersed in space. Three types of scattering occur. They are called Rayleigh scat t ering , Stokes scattering, and anti-Stokes scattering. Rayleigh scattering occurs as a result of elastic collisions between the photons and the molecules in the sample; no energy is lost on collision. Some of the photons are scattered with less energy after their interaction with molecules and some photons are scattered with more energy. These spectral lines are called Raman lines

5. The Raman–Stokes lines are from those photons scattered with less energy than the incident radiation; the Raman–anti-Stokes lines are from the photons scattered with more energy . The differences in the energies of the scattered photons from the incident photons have been found to correspond to vibrational transitions . Figure : Shows the process of Rayleigh and Raman scattering.

6. INSTRUMENTATION Instrumentation for modern Raman spectroscopy consists of three component Light Source Samples and Sample Holders for Raman Spectroscopy Suitable Spectrometer Figure: Idealized layout of a Raman spectrometer

7. Light Source: Monochromatic light sources are required for Raman spectroscopy. The light sources used originally were simple UV light sources, such as Hg arc lamps. The Raman signal is directly proportional to the power of the light source. Modern Raman instruments use a laser as the light source. Some common Laser sourses for Raman spectroscopy are Laser Type Wavelength, nm Argon ion 488.0 or 514.5 Krypton ion 530 or 514 Hellium -neon 632.8 Diode 785 or 830 Nd -YAG 1064

8. Samples and Sample Holders for Raman Spectroscopy: Because the laser light source can be focused to a small spot, very small samples can be analyzed by Raman spectroscopy. Liquid samples can be held in beakers, test tubes, glass capillary tubes, or NMR tubes. Aqueous solutions can be analyzed, since water is a very weak Raman scatterer . This is an advantage for Raman spectroscopy over IR. Other solvents that can be used for Raman studies include chloroform, carbon tetrachloride, acetonitrile, and carbon disulfide .

9. Raman Spectrometers: Raman spectrometers were similar in design and used the same type of components as the classical ultraviolet/visible dispersing instruments . Most employed double grating systems to minimize the spurious radiation reaching the transducer. Photomultipliers served as transducers. Now Raman spectrometers being marketed are either Fourier transform instruments equipped with cooled germanium transducers or multichannel instruments based upon charge-coupled devices.

10. APPLICATION Quantitative and qualitative analyses of inorganic and organic compounds can be performed by Raman spectroscopy. Raman spectroscopy is used for bulk material characterization , online process analysis, microscopic analysis, and chemical imaging of inorganic, organic and organometallic compounds, polymers , biological systems etc. Raman spectra have fewer lines and much sharper lines than the corresponding IR spectra. This makes quantitative analysis, especially of mixtures, much simpler by Raman spectroscopy than by IR spectroscopy . Another use of Raman spectroscopy for quantitative analysis is the determination of percent crystallinity in polymers.

11. Quantitative analysis requires measurement of the intensity of the Raman peaks and the use of a calibration curve to establish the concentration –intensity relationship. The intensity of a Raman peak is directly proportional to the concentration.

12. REFERENCE Robinson W. J. & Frame S. M. E.: Undergraduate Instrumental Analysis, Sixth Edition: 290-302

13. OPEN TO DISCUSSION

14. THANK YOU