UV-VISIBLE SPECTROSCOPY 1 1 instrumation .pptx

Ima

1. UV-VISIBLE SPECTROSCOPY  PRESENTED BY :  VAISHNAVI SONAR  POOJA DALWALE JANAVI MAHAJAN GUIDED BY : Mr. ATUL PATIL SIR

2. INTRODUCTION SPECTROSCOPY : Spectrum, means light and Scopy, means examination. It is the study of interaction of matter with light or electromagnetic radiations. Light : Also called as electromagnetic radiations i.e. it consists of both the electronic and magnetic radiations. It contains energy packets called as photons.

3. PRINCIPLE OF SPECTROSCOPY ABSORPTION EMISSION Ground state Excited state  Emission of energy Absorption of energy

4. ENERGY = e 1 -e 0  UV-VISIBLE SPECTROSCOPY It is based on the principle of absorption spectra . When a molecule absorbs ultraviolet radiation , the electron in that molecule undergoes transition from lower to a higher energy level i.e. from the ground state to the excited state. The actual amount of energy required depends on the difference in energy between the ground state and excited state. Let e = energy of ground state       e 1   = energy of excited state        Range of UV-VISIBLE SPECTROSCOPY = 200-800 nm.

5. Electronic transitions Energy absorbed in the ultraviolet region produces changes in the electronic  energy of the molecules resulting from transitions of valence electrons in the molecule . Three distinct types of electrons are involved in organic molecules as … σ Electrons :  these electrons are involved in saturated bonds,called as                        2) π Electrons :  these electrons are involved in unsaturated bonds,called  Electrons :  these are the electrons which are not involved in bonding 3) n Sigma bonds. Pie bonds (lone pairs).

6. TYPES OF ELECTRONIC TRANSITIONS

7. * σ - σ =  The energy required is large. 2)   π - π * = Compounds which have multiple bonds like alkenes , alkynes , nitriles , aromatic compounds 3) n - σ * = Saturated compounds containing atoms with lone pairs like O,N,S and halogens 4) n - π * = Compounds containing double bond with hetero atoms C=O , N=O Other two transitions are forbidden and are only theoretically possible E.g. methane(CH 4 ),Ethane(C 2 H 6 ). Absorbance maxima at 125 nm.

8. Principle of UV-VISIBLE spectroscopy BEER'S LAW : It states that the amount of absorbed light is proportional to the solution concentration. LAMBERT'S LAW : It states that absorbance of the light is directly proportional to the path length or thickness. Equation 1 = A α C Equation 2 = A α L

9. Terminology  

10. Absorption shifts  Red shift Blue shift

11. Instrumentation  Source  Monochromator                                                                                                                                            Cuvette for sample  Detector  Read out system   Filters Prisms Grating  

12. Sources  Hydrogen discharge lamp : Hydrogen gas stored under relatively high pressure. When electric discharge passed through the lamp excited hydrogen molecules will emit UV radiations. Deuterium lamp : sImilar to hydrogen lamp but has deuterium in place of hydrogen. Xenon lamp : Xenon is filled at 10-30 atm pressure and has two tungsten electrodes. Intensity is greater than hydrogen lamp. Mercury lamp : It contains mercury vapour and gives bands which are sharp. But it is not widely used.

13. Mercury lamp Xenon lamp Hydrogen lamp

14. Monochromators  Filters : It helps in controlling the flow of light. Also it keeps apart certain wavelengths. Prisms : It is made of quartz for use in UV . when light passes through it, it gets spread out instead of mixed up. Grating : It helps in getting monochromatic light which passes through the sample and then to the detector.

15. CUVETTE OR SAMPLE HOLDER Cuvettes are constructed with optically flat fused glass. It is a small rectangular tube to hold the samples, having two frosted sides.

16. Detectors   It is a device which detects the energy of an incident beam and of a transmitted beam. The difference between these two beams indicates the energy absorbed by an analyte. It converts the light energy into electrical signals, that are displayed on readout system. Types   :  Photomultiplier tube  Barrier layer cell   Photodiodes  Photocell

17. Barrier layer cell detector   It consists of two electrodes one is made of iron and other is silver or gold film. In between these two electrodes there is semiconductor selenium which separates two electrodes. When light radiations falls on selenium layer electrons become mobile and moves towards respected electrodes it creates potential difference and cause flow of current.

18. Barrier layer cell

19. Photocell It consists of two electrodes enclosed in an evacuated tube. Cathode is specially designed as a half cylinder which is coated from inside with light sensitive material. Anode is in the form of rod or plate and it is placed against the cathode. Quartz or fused silica window is provided for the passage of the transmitted light.

20. Photocell 

21. Photomultiplier tube It has 1 cathode and 9-16 dynodes ( it serves as an electron multiplier through secondary emission ) which is enclosed in evacuated tube. They are coated with a thin layer of a photosensitive material. Dynode is made up of Be-Cu. Each dynode is placed at higher potential than previous dynode .

22. Photomultiplier tube

23. Types Of UV-Visible Spectroscopy SINGLE BEAM SPECTROPHOTOMETER

24. 2 .DOUBLE BEAM SPECTROPHOTOMETER

25. APPLICATIONS Qualitative analysis  Quantitative analysis Detection of impurities Structural elucidation of organic compounds

26. Thank You!