Uv visible spectroscopy

UV-VISIBLE SPECTROSCOPY

1. UV-VISIBLE SPECTROSCOPY SUBMITTED BY: SUBMITTED TO: UDAYPAL Dr.MUNISH SIR CUHP20PLS30

2. WHAT IS SPECTROSCOPY…..? The study of interaction of electromegnetic radiation with the matter of inerest Mainly by: Absorption Emission Scattering ELECTROMEGNETIC RADIATION: a kind of radiation including visible light, radio waves, gamma rays, and X-rays, in which electric and magnetic fields vary simultaneously.

3. Wavelength range of UV-VISIBLE Light: Wavelength range of UV light— 180-350nm Wavelength range of VISIBLE light– 350-800nm Wavelength range of UV-VISIBLE light- - 180-800nm

4. PRINCIPLE: Beer’s law: Absorbance of monochromatic light is directly proportional to the concentration of solution Lambert’s law:   Absorbance of monochromatic light is directly proportional to the pathlength of solution Molar absorption coefficient specific for every solution and wavelength Beers-Lamberts law:

5. Types of Transitions In UV spectroscopy molecule undergo electronic transition involving sigma, pi and n electrons. So it is also often called as electronic spectroscopy. Four types of electronic transitions are possible.

6. INSTRUMENTATION: Radiation source for UV region :- H discharge lamp,deuterium lamps and xenon discharge lamp Both deuterium and hydrogen lamps emit radiation in the range 160- 375nm. For visible region :- Tungston filament lamp use for region 350-2000nm.

7. Monochromater : It is a device used to isolate the radiation of the desired wavelength from wavelength of continous spectra Essential elements of monochromater are: 1.Entrance slit 2.Prism 3. Exit slit Beam splitter: -split monochromatic light Blank sample: A blank is  a sample that contains everything except for the analyte of interest( solvent,buffer,water,etc ) Sample : filled in sample cuvette Photodetector : The photodiode  converts light into electrical signals and temporarily stores them . Quartz prism used in uv - region Glass prism used in visible region spectrum

8. Working:- A double beam spectrophotometer utilizes two beams of light:  a reference beam and a sampling beam that passes through the sample. Double beam spectrophotometers have two detectors that allow the two beams to be measured at one time. L oad reference sample in reference cuvette and sample in sample cuvette Compare absorbance of sample and reference Absorbance is directly proportional to density of solution

9. Applications: . Detection of impurities: Additional peaks can be observed due to impurities in the sample and it can be compared with that of standard raw material. Structural elucidation of organic molecules:- UV spectroscopy is useful in the structure elucidation of organic molecules, the presence or absence of unsaturation , the presence of hetero atoms. From the location of peaks and combination of peaks, it can be concluded that whether the compound is saturated or unsaturated, hetero atoms are present or not.

10. Quantitative analysis:- UV absorption spectroscopy can be used for the quantitative determination of compounds that absorb UV radiation. This determination is based on Beer’s law Qualitative analysis :- . Identification is done by comparing the absorption spectrum with the spectra of known compounds. UV absorption spectroscopy is generally used for characterizing aromatic compounds and aromatic olefins Chemical kinetics:- Uses to determine amount of product and substrate.

11. Advantages Simple and inexpensive instrumentation Most organic molecules absorb UV/Vis light Quantitative (Beer’s law) Disadvantages Mixtures of molecules can be problem due to overlap(hence requires significant sample preparation. Spectra are not highly specific for particular molecules. Absorption can be dependent on solution conditions.

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