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Tristan Ursell APh 162 California Institute of Technology. Beer’s Law and Spectrophotometry . Two-fold: - Relates concentration to the optical measurement of ‘absorbance’ - combined with spectrophotometry can be used to distinguish and compare different molecules in
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Tristan Ursell APh 162 California Institute of Technology Beer’s Law and Spectrophotometry
Two-fold: - Relates concentration to the optical measurement of ‘absorbance’ - combined with spectrophotometry can be used to distinguish and compare different molecules in solution Uses of Beer’s Law:
Conceptual Basis of Beer’s Law • - Light of a particular wavelength enters the ‘sample’. • Light scatters from particles in solution (no momentum change) reducing light transmission • - Light is absorbed by molecules/particles (momentum • change) and remitted at different wavelengths, reducing light transmission
A little more In-depth: Beer’s Law is stated in a way to make certain quantities easy to compare and interpret. Parameters: l – sample pathlength (usually 1cm) c – concentration (mol/vol) – molar absorption coefficient ( ) I – light intensity (W/m^2)
When can I use Beer’s Law? Rule of Thumb: A<1 for accurate results Only at low concentrations, where the absorbance is linear (single scattering event):