FORS-2107EL Lecture Notes - Lecture 7: Thermal Decomposition, Equilibrium Constant, Ionic Strength
27 Jun 2018
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Forensic Science - Day 7 2018.02.05
Fluorescence
-Things that are not fluorescent release all their excitation energy through heat
-Therefore, if heat is added then we can reduce the fluorescence released
-So if heat is added then we can reduce the fluorescence released
-Heat is the mean kinetic energy of the molecules
-In practice, there are always orange goggles used with ALS so that it can filter out the
excitation wavelengths (radiation) in order to be able to properly see fluorescence,
therefore only emitted wavelengths are seen
-From the equation on the right, we can see
-Fluorescence intensity is proportional to
fluorophore concentration
-Fluorescence intensity is proportional to
the incident power applied
-Fluorescence intensity is dependent upon
two terms that are related to the
fluorophore environment, the temperature
and solvent
-Phi = the fraction of excited molecules which will relax by fluorescent emission
(function of solvent, temp, and presence of quenchers)
-Advantages and limitations of Fluorescence Spectroscopy
-Advantages
-Significantly more sensitive than absorptive methods
-Selectivity can be enhanced by wise choosing of both λexc and λem
-Disadvantages:
-may require labeling when used as detection scheme in chromatography,
electrophoresis
-Environmentally sensitive – quenchers, solvent, etc.
Application of Fluorescence Spectroscopy
-The common wavelength used for fluorescence is 450 nm
-An interference filter only allows specific waves of light at specific wavelengths to
pass, this is used to increase the selectivity of the fluorescence in a stain and
therefore decrease the limit of detection
-The same sample must be treated as a complex mixture, and therefore optical
spectroscopy interrogates everything in the light path, not just the desired substance
-This can cause superimposed results of everything in the mixture
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Document Summary
Things that are not uorescent release all their excitation energy through heat. Therefore, if heat is added then we can reduce the uorescence released. So if heat is added then we can reduce the uorescence released. Heat is the mean kinetic energy of the molecules. In practice, there are always orange goggles used with als so that it can lter out the excitation wavelengths (radiation) in order to be able to properly see uorescence, therefore only emitted wavelengths are seen. From the equation on the right, we can see. Fluorescence intensity is proportional to the incident power applied. Fluorescence intensity is dependent upon two terms that are related to the. Phi = the fraction of excited molecules which will relax by uorescent emission (function of solvent, temp, and presence of quenchers) Selectivity can be enhanced by wise choosing of both exc and em. May require labeling when used as detection scheme in chromatography, electrophoresis.
