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Which of the undermentioned factors causes non-linearity of Boer-Lambert law at high concentration ?

  • A.Dissociation of analytes in solution
  • B.Analyte turning to be fluorescence in nature
  • C.Electrostatic interaction between species reducing absorption
  • D.Reaction between analyte and the solvent

Answer: C

The cause is electrostatic interaction between species reducing absorption.

The Beer-Lambert law assumes that absorbing molecules act independently. At high concentrations, usually above about 0.01 M, they are close enough for electrostatic interactions between them to alter their charge distribution and so their ability to absorb at a given wavelength. The molar absorptivity changes and the plot of absorbance against concentration curves away from a straight line.

Dissociation and reaction with the solvent are chemical deviations caused by equilibria, which can occur at any concentration and are not the high-concentration effect. Fluorescence is an instrumental or sample interference, not the cause of non-linearity at high concentration.

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