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

2. Terms & Symbols

3. Beer’s Law log Po/P = ebc = A The derivation of this law assumes
That the incident radiation is monochromatic.
The absorption occurs in a volume of uniform cross-section.
The absorbing substances behave independently of each other in the absorbing process.

4. Beer’s Law Limitations to Beer’s Law Real Limitations to Beer’s Law
Apparent Chemical Deviations
Apparent Instrumental Deviations with Polychromatic Radiation
Instrumental Deviations in the Presence of Stray Radiation

5. The Effects of Instrumental Noise on Spectrophotometric Analyses
Types of Noise
Shot noise – This noise is generated by current flowing across a P-N junction and is a function of the bias current and the electron charge. The impulse of charge q depicted as a single shot event in the time domain can be Fourier transformed into the frequency domain as a wideband noise.
Thermal noise – In any object with electrical resistance the thermal fluctuations of the electrons in the object will generate noise.
White noise- The spectral density of thermal noise is flat with frequency.
Burst noise – Occurs in semiconductor devices, especially monolithic amplifiers and manifests as a noise crackle.

6. The Effects of Instrumental Noise on Spectrophotometric Analyses
Types of Noise
Avalanche noise – Occurs in Zener diodes are reversed biased P-N junctions at breakdown. This noise is considerably larger than shot noise, so if zeners have to be used as part of a bias circuit then they need to be RF decoupled.
Flicker noise – This noise occurs in almost all electronic devices at low frequencies. Flicker noise is usually defined by the corner frequency FL.
Sources of Noise
Case I: sT = k1
Case II: sT = k2(T2 + T) ½
Case III: sT = k3T

7. The Effects of Instrumental Noise on Spectrophotometric Analyses
Effect of Slit Width on Absorbance Measurements

8. Instrumentation Instrument Components Sources Wavelengths selectors
Sample containers
Radiation detectors
Signal processors and readout devices

9. Instrumentation Sources- Light sources Deuterium and Hydrogen Lamps
Tungsten Filament Lamps

10. Instrumentation Types of Instruments Single-beam Double-beam in space
Double-beam in time
Multichannel

11. Instrumentation
Single-Beam Instruments

12. Instrumentation
Double-Beam Instruments

13. Instrumentation Typical Instruments Photometers Visible Photometers
Probe-type Photometers
Ultraviolet Absorption Photometers
Spectrophotometers

14. Instrumentation Most common spectrophotometer: Spectronic 20.
On/Off switch and zero transmission adjustment knob
Wavelength selector/Readout
Sample chamber
Blank adjustment knob
Absorbance/Transmittance scale

15. Instrumentation
Visible Region

16. Instrumentation
Single-Beam Instruments for the Ultraviolet/Visible Region

17. Instrumentation Single-Beam Computerized Spectrophotometers
Inside of a single-beam spectrophotometer connected to a computer.

18. Instrumentation Double-Beam Instrumetents
Double-Dispersing Instruments
Diode Array Instruments

19. References http://www.anachem.umu.se/jumpstation.htm