[positiveion]

Why does the beer-lambert law not apply for higher concentrations?

[renge ishyo]

In dilute solutions the analytes of interest are separated far enough away from each other that you can essentially ignore interactions that might lead to a lower than actual measured concentration. For example, suppose we have an analyte that absorbs at 420 nm. If it comes in contact with another copy of itself it might form a dimer which does not absorb at all at 420 nm. In dilute solutions, the chance of the two analytes randomly bumping into each other in solution is low, so each analyte is measured independently at 420 nm and absorbance is proportional to the amount of analyte present. However, in solutions that are concentrated, two analytes could very well come together and you wouldn't detect the presence of either of them at 420 nm. Hence, Beer's Law gives inaccurate measurements when things get too concentrated (it cannot detect the dimeric forms and reports a lower than actual concentration).

[Mitch]

That's a great explanation. I never gave it that much thought.

[renge ishyo]

Thankya