Other than high concentration, for what other conditions might the Beer Lambert law not be obeyed?

Answer 1

Beer's law can be thought of as a first order approximation. There are several situations in which deviations from Beer's law are encountered.
1. Inhomogeneous media may have a significant scattering cross section that adds to the effect of the absorption cross section. In careful work the scattering cross section is estimated independently. Scattering is particularly important in spectroscopy of turbid systems, such as tissue.
2. If a sample contains chemical species A and B, then the absorption spectrum is not A + B as predicted by Beer's law, but rather A + B + AB, where AB represents the interaction between A and B. Non-linear models such as partial least squares (PLS), principle component analysis (PCA) or neural networks (NN) are used to model mixtures in place of Beer's law.
3. Photo bleaching can occur, particularly in laser spectroscopy. Beer's law is based on the assumption that virtually all of the absorbing species are in the ground state to begin with. If the incident illumination is high enough, a significant fraction of the absorbing species may be in excited states. Non-linear optical effects are also found in the high intensity regime.

Answer 2

The beer-lambert law is only obeyed over the range of concentration that can be measured by the technique you are using. If you are measuring the concentration indirectly using the reaction with a dye or something then the limit would be the concentration of the dye. Also most spectrometers have a set detection range anything above that will not be measured and anything below that will be highly inaccurate. There are also occasions when the E (sorry can't do the symbol on this page) is different under different conditions or folding of the substance you are measuring. For example when measuring protein concentration the position of the aromatic residues makes a difference to the E as they are responsible for the majority of the absorbance.

Answer 3

If you get drunk and oversleep, missing the exam. Then Beer-Lambert's second law (that he who drinketh Beer with Lambert on the eve of an important occasion gets what he deserves) comes into play.