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+ Photochemistry
+ Spectroscopy
+ Spectrophotometry
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Kevin Yeh

Lambert Beer's law deviations

Bertrand Wengher  Follow

A compound S follows the Lambert-Beer law if the absorbance $E_\lambda$ at a particular wavelength $\lambda$ is proportional to the concentration $c$ of S.

\[E_\lambda = \left(\frac{I_0}{I} \right) = \epsilon\cdot c \cdot d \]

A "deviation" is observed when the real concentration $c$ is different from the expected/assumed.

This may happen if

  1. S is an acid or a base:
    • variation of the pH leads to (de)protonation and forms another species with a completely different absorption spectrum, or at least a different $\epsilon$ at the wavelength under observation
  2. S undergoes a reaction to S' (with different optical properties) at elevated temperatures (or change of pH)
  3. Decrease of temperature or change of pH leads to the formation of a turbid solution from which light is scattered into the detector

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