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UV/VISIBLE SPECTROSCOPY SAMPLE



Absorption peak CH3



excited state* E CH3



Frequency 1.5 x 1015 Hz to 3.7 x 1014 Hz approx. Wavelength 190 nm to 800 nm.



Wavelength ground state Electronic excitation of sample



UV Region



400nm



Visible Region



430 nm 800 nm



Violet Blue



A = εcL Absorbance = molar x extinction coefficient (dm3 mol-1 cm-1)



concentration (mol dm-3)



x



path length (cm)



Red



Visible Region Colour Wheel



UV/VIS Spectrum of Potassium Permanganate



Orange



Green Yellow



600 nm



560 nm



…it appears as this colour



Sample Preparation FLOW CELL



Solution Cuvettes



The plot of absorbance v concentration is linear if the Beer-Lambert law is obeyed



absorbance



490 nm



Absorption due to transitions between electronic levels in molecules



The BeerBeer-Lambert Law



190nm If a substance absorbs here… here…



SPECTRUM



Absorbance



SOURCE Visible – Tungsten/Halogen Lamp UV – Deuterium Lamp



DETECTOR



GAS CELL



• Variable path length • Typically silica for UV • Glass or Polystyrene for visible



Wavelength (nm)



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