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Lecture 19
Spectrophotometry-III
Light Source
Sample
Monochromator(filter,
wavelength selector)
Detector
Spectrometer
Data Processing
Single beam
Double beam
A tungsten lamp
3000 K
Deuterium Lamp
hHHHEH '''202
Deuterium: higher intensity
UV sources
Limits to Beer’s Law
strayP
strayPT
0
1
Incident light
P0
Emergent light
P1
Stray light
Solvents for UV/vis Spectrophotometry
Solvent Lower Wavelength Limit
Water 180 nm
Ethanol 220 nm
Hexane and 200 nmCyclohexane
Acetone 320 nm
AClT logBeer’s law Bugert, Lambert and Beer
A
concentration
Straight line!
Wavelength, nm
Aor
B
Other components of the mixture
Measure @this wavelength!
Limits to Beer’s Law
Polychromatic light (several wavelength)
Wavelength, nm
Aor
B
Other components of the mixture
Intensity is too low!
Wavelength, nm
Aor
B
Other components of the mixture
Measurement is difficult
Wavelength, nm
Aor
C
Other components of the mixture
Measure @this wavelength!
B + reagent CCompound is chemically derivitized (transformed) prior to themeasurement of absorbance