Chapter 13 - Chapter 13 An Introduction to...

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Chapter 13 An Introduction to Ultraviolet/Visible Molecular Absorption Spectrometry Absorption measurements based upon ultraviolet and visible radiation find widespread application for the quantitative determination of a large variety species. Beer’s Law: A = -logT = logP 0 /P = ε bc A = absorbance ε = molar absorptivity [M -1 cm -1 ] c = concentration [M] P 0 = incident power P = transmitted power (after passing through sample)
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Measurement of Transmittance and Absorbance: The power of the beam transmitted by the analyte solution is usually compared with the power of the beam transmitted by an identical cell containing only solvent. An experimental transmittance and absorbance are then obtained with the equations. P 0 and P refers to the power of radiation after it has passed through the solvent and the analyte. T P P P P s o l u t i o n s o l v e n t = = 0 A P P P P s o l v e n t s o l u t i o n = ≈ l o g l o g 0
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Derivation of Beer’s Law: Sample cell with absorbing molecules P 0 P b=0 b=b db P P-dP
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dP P Incremental power lost power in; i.e., increase power in, increase power absorbed dP db Longer pathlength, greater number
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This note was uploaded on 05/06/2010 for the course CHEM 4414 at Arkansas Tech.

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Chapter 13 - Chapter 13 An Introduction to...

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