1. Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
An Introduction to Ultraviolet/Visble Molecular Absorption Spectrometry
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13
Chapter 13

2. Reflection and Scattering Losses
Transmission P P0
T = P/P0
%T = (P/P0)*100
A = - log T
Reflection
Reflection
Reflection
Reflection
Reflection
Scattering

3. Application of Beer’s Law to Mixtures
Atotal = A1 + A2 + A3 +… +An= e1bc1 + e2bc2 + e3bc3 +… +enbcn

4. Limitation to Beer’s Law
Real Limitations to Beer’s Law
Applies to concentrations < 0.01M
e depends on refractive index of the medium en/(n2+2)
Apparent Chemical Deviation
HIn In-+H+

5. Chemical Deviation from Beer’s Law for Unbuffered Solution of an Indicator
1.000
0.800
l = 430
0.600
Absorbance
0.400
l =570
0.200
4.00
8.00
12.00
16.00
Indicator concentration M*105

6. Limitation to Beer’s Law
Apparent Instrumental Deviation with Polychromatic Radiation
For l’
A’=log (Po’/P’) = e’bc
Po’/P’ =10 e’bc
P’ = Po’*10 -e’bc
for l’’
P’’ = P0’’*10 -e’’bc
Am=log (Po’ +Po’’)/ (P’+P’’)
Am=log (Po’ +Po’’)/ (Po’*10 -e’bc+P0’’*10 -e’’bc)
Am=log (Po’ +Po’’) – log (Po’*10 -e’bc+P0’’*10 -e’’bc)
e’ = e’’ Am= e’bc

7. Deviation From Beer’s Law With Polychromatic Light
1.000
0.800
e1 =1500
e2=500
0.600
e1 =1750
e2=250
Absorbance
0.400
0.200
4.00
8.00
12.00
16.00
Indicator concentration M*104

8. The Effect of Polychromatic Radiation upon Beer’s Law
Band A
Band A
Band B
Absorbance
Absorbance
Band B
Wavelength
Concentration

9. Limitation to Beer’s Law
4. Instrumental deviation in the presence of stray radiation
PS/Po *100
0.00%
0.2%
1.0%
Absorbance
5.0%
Concentration

10. Instrumentation
Sources
D2 lamp
Tungsten lamp
Xenon lamp

11. Instrument components
Sources
Deuterium and Hydrogen Lamps
D2+Ec D2* D’ + D’’+ hn
Ec = E D2* = ED’+ED’’+ hn nm

12. Deuterium Lamp
Ceramic electrode
Anode
Aperature
Cathode
Bulb

14. Tungsten Lamps oK nm
Tungsten Lamp
2870oK nm

15. The Halogen Tungsten Lamp
W +I WI2
3500oK

17. Xenon Flash Lamp
Cathode
Anode
Triggers
Triggers
2 cm
Cathode
Anode

20. Types of Instruments Single beam Double beam Multichannel In time
In space
Multichannel

21. Instrument Designs Single beam Filter or monochromator Photodetector
Amplifier
Readout
Source l1 l2
18.88
Reference cell
Sample cell

22. Instrument Designs
Double beam in space l1 l2
18.88
Beam splitter

23. Instrument Designs Double beam in time Grid mirror Sector mirror 18.88

24. Multichannel Spectrophotometer
Instrument Designs
Multichannel Spectrophotometer
Photodiode array
Source
Grating
Sample

25. Instrument Designs Probe type photometer Tungsten lamp Photodiode `
Interference filter
Optical fiber
Return light path
Mirror

26. Optical Diagram of Spectronic 20
Entrance slit
Field lens
Objective lens
Grating
Tungsten lamp
Filter
Light control
Measuring
phototube
Sample
Exit slit
Wavelength cam

27. Double Beam Spectrophotometer
Photomultiplier
Deuterium lamp
Tungsten lamp
Reference
Grid mirror
Concave grating
Sample
Sector mirror

28. Double Beam Recording Spectrophotometer
Entrance slit
Double Beam Recording Spectrophotometer
Exit slit
Collimating mirror
Reference toroid
mirror
Reference compensator mirror
Rotatable
grating
Oprical chopper
Filter
assembly
Reference spherical
mirror
Reference
cuvette
Sample cuvette
Deuterium lamp
Transducer
Selector
mirror
Entrance aperature
Entrance toroid
mirror
Chopper back-up mirror
Tungsten lamp
Sample spherical
mirror
Exit toroid
mirror
Sample comensator mirror