Basic Principles of Spectrophotometry

Basic Principles of Spectrophotometry - BASIC...

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Unformatted text preview: BASIC SPECTROPHOTOMETRY BASIC PRINCIPLES OF SPECTROPHOTOMETRY 1 Principles of Light Measurement • Properties of light and energy (Photons) – Wavelength – Amplitude (intensity, brightness) – Frequency (waves / second) – Relationships: E = hf; f = c/! 2 3 1 BASIC SPECTROPHOTOMETRY 4 • Energies of atoms and molecules 5 6 2 BASIC SPECTROPHOTOMETRY 7 8 • Transmission/Absorption of light – Reflection = bouncing – Refraction = bending – Diffusion = spreading – Diffraction = combination of all three – wavelength isolation • filters • Prisms -- non-linear • Diffraction gratings -- linear 9 3 BASIC SPECTROPHOTOMETRY 10 11 12 4 BASIC SPECTROPHOTOMETRY 13 Absorption / Emission of light – Atoms – Molecules – Solids 14 15 5 BASIC SPECTROPHOTOMETRY Laws of Absorbance • Beer / Lambert Laws • Absorbance vs. %Transmittance • Formulas 16 17 18 6 BASIC SPECTROPHOTOMETRY 19 20 21 7 BASIC SPECTROPHOTOMETRY 22 23 24 8 BASIC SPECTROPHOTOMETRY 25 Spectrophotometer Components • Power supply • Light Source -- halogen quartz – Collimating lenses -- organize parallel lines – Focusing lenses -- narrow or intensify beam • Monochromator – Band pass – Stray light = band width at ½ band height (room light, scratches, dust, fingerprints, wide bandpass) – Slit width -- exit slit 26 • Sample cell -- quartz or sliica • Photodetector – Photomultiplier tube: • Read-out device -- cathode, dynodes, anode digital, recorder, printer 27 9 BASIC SPECTROPHOTOMETRY 28 29 30 10 BASIC SPECTROPHOTOMETRY 31 32 33 11 BASIC SPECTROPHOTOMETRY 34 35 36 12 BASIC SPECTROPHOTOMETRY 37 Analytical Problems • Absorbance Variation – Check photometric accuracy with Neutral Density filters • Noise and Drift – Recorder or oscilloscope • Stray Light – Check with sharp cut-off filters • Linearity – Dye solutions • Wavelength – Filters: holmium oxide or didymium 38 13 ...
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This note was uploaded on 09/23/2012 for the course MDLB 4200 taught by Professor Larryschoeff during the Spring '08 term at Utah.

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