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Can somebody explain as concrete as possible, how the change of temperature and the change of pH leads to deviations of this law?

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  • $\begingroup$ I don't understand what you mean. Lambert Beer law apply for fixed temperature and pH. $\endgroup$ – user1420303 Mar 18 '15 at 15:41
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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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