Ultraviolet & visible spectroscopy
Download as PPTX, PDF2 likes2,307 views
UV-visible spectroscopy responds to electronic transitions involving pi and lone pair orbitals and is used to identify conjugated systems which tend to have stronger absorption. There is no single light source for the entire UV and visible region, with tungsten lamps used for the visible region and deuterium lamps for the ultraviolet region. Samples are typically held in quartz due to absorption of UV by glass, while solvents must be transparent in the region being observed and commonly lack conjugated systems or carbonyls. UV-visible spectroscopy can be used in the oils industry to detect trans isomers, determine purity, and estimate components like oryzanol, gossypol, and chlorophyll.
Ultraviolet & visible spectroscopy
- 1. Ultraviolet & visible spectroscopy UV-VISIBLE SPECTROSCOPY RESPONDS TO TRANSITION INVOLVING PIE AND LONE PAIR ORBITALS & IS USED FOR IDENTIFYING CONJUGATED SYSTEMS WHICH TENDS TO HAVE STRONGER ABSORPTION.
- 3. SOURCE OF LIGHT FOR UV-VIS THERE IS NO SINGLE LIGHT SOURCE FOR THE ENTIRE UV & VISIBLE REGION. TUNGSTEN LAMP-VISIBLE REGION DEUTERIUM LAMP-ULTRAVOILET REGION.
- 4. SAMPLE HOLDER & MONOCHROMATOR SAMPLE HOLDER IS GENERALLY MADE UP OF QUARTZ CRYSTAL BECAUSE GLASS DO ABSORBS AT UV REGION. HOWEVER GLASS HOLDER FOR SCANNING IN UV REGION. MONCHROMATOR IS GENERALLY GRAFTER OR ROTATING PRISM. PHOTODIODE ARRAYS ARE NOW AVAILABLE WHICH PRODUCES ACCURATE WAVELENGTH.
- 5. SOLVENT SELECTION Solvents must be transparent in the region to be observed; the wavelength where a solvent is no longer transparent is referred to as the cutoff Since spectra are only obtained up to 200 nm, solvents typically only need to lack conjugated systems or carbonyls
- 6. SOLVENT SELECTION Common solvents and cutoffs: acetonitrile 190 chloroform 240 cyclohexane 195 1,4-dioxane 215 95% ethanol205 n-hexane 201 methanol 205 isooctane 195 water 190
- 7. APPLICATION IN OILS INDUSTRY UV IS TO HPLC WHAT MS IS TO GC. UV VIS ABSORPTION SPECTROSCOPY CAN BE USED TO DETECT TRANS ISOMER SINCE TRANS ABSORBS . USED TO DETERMINE PURITY OF THE SAMPLE. ESTIMATION OF CONJUGATED ISOMERS IN ALKALI ISOMERISED LINSEED OIL. ESTIMATION OF ALPHA & BETA ELEOSTEARIC ACID IN TUNG OIL
- 8. APPLICATION IN OILS INDUSTRY DETERMINATION OF ORYZANOL CONTENT IN RICE BRAN OIL. ESTIMATION OF GOSSYPOL IN COTTONSEED OIL. ESTIMATION OF CHLOROPHYLL IN OIL ESTIMATION OF PHOSPHORUS CONTENT