Lambert Beer's law deviations

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




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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