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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asked Mar 18, 2015 at 15:06
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$\begingroup$ I don't understand what you mean. Lambert Beer law apply for fixed temperature and pH. $\endgroup$– user1420303Commented Mar 18, 2015 at 15:41
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1 Answer
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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
- 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
- S undergoes a reaction to S' (with different optical properties) at elevated temperatures (or change of pH)
- Decrease of temperature or change of pH leads to the formation of a turbid solution from which light is scattered into the detector
answered Mar 18, 2015 at 15:54