Basic Principles of Spectrophotometry - BASIC...

Basic Principles of Spectrophotometry
Download Document
Showing page : 1 of 13
This preview has blurred sections. Sign up to view the full version! View Full Document
This is the end of the preview. Sign up to access the rest of the document.

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 ...
View Full Document