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

2. Terms & Symbols

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

4. Beers Law Limitations to Beers Law Real Limitations to Beers 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: s T = k 1 Case II: s T = k 2 (T 2 + T) ½ Case III: s T = k 3 T

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. 1.On/Off switch and zero transmission adjustment knob 2.Wavelength selector/Readout 3.Sample chamber 4.Blank adjustment knob 5.Absorbance/Transmittanc e 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 spectrophot ometer connected to a computer.

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

19. References http://www.anachem.umu.se/jumpstation.htm http://userwww.service.emory.edu/~kmurray/mslist.html http://www.anachem.umu.se/jumpstation.htm http://userwww.service.emory.edu/~kmurray/mslist.html http://www.anachem.umu.se/jumpstation.htm http://www1.shimadzu.com/products/lab/spectro/uv3150.html http://www.perten.com/product_range/diode_array/da_technology.html http://repairfaq.ece.drexel.edu/sam/CORD/leot/course10_mod03/mod1 0-03.html http://las.perkinelmer.com/catalog/Product.aspx?ProductID=L950 http://www.olisweb.com/products/upgrades/ir983.php http://imagers.gsfc.nasa.gov/ems/visible.html http://biology.easternct.edu/courses/spectwenty.htm http://www.cairnweb.com/systems/prod_lamp.html http://www.odyseus.nildram.co.uk/RFIC_Theory_Files/Noise_Tutorial.p df