[Lynda92]

why isn't beer's law (A=εcl) accurate at high concentrations? i.e. the absorbance-concentration graph becomes non linear at high concentrations

[rabolisk]

http://en.wikipedia.org/wiki/Beer%27s_law

There's a brief explanation there.

[JGK]

Basically, for a 1 cm cell an increase of 1 AU reduces the transmitted light hitting the detector by an order of magnitude:
0 AU - 100% of the focussed light passes through the sample to the detector.
1 AU - only 10% of the focussed light passes through the sample to the detector.
2 AU - only 1% of the focussed light passes through the sample to the detector.
3 AU - only 0.1% of the focussed light passes through the sample to the detector.


So if the absorbance is high the detector may not be sensitive enough to detect the changes to accurately measure concentration.

Ideally, I was always taught to keep any measurents with the range 0.1 - 1.0 AU for best results.