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
C2H5N
S-
SC2H5Cu
S
S S
SN
C2H5
C2H5
NC2H5
C2H52 +
Cu2+
NH
NN
S
N
Hg
N
S
NN
HN
N
H
N N
SH
NHg2+
NO2
NO2
HNNH2
+O
NO2
NO2
HNN