# Beer-Lambert equation

by nobahar
Tags: beerlambert, equation
 P: 503 1. The problem statement, all variables and given/known data I need to use the Lambert-Beer equation to plot optical density of a lactate solution. 2. Relevant equations $$A=\varepsilon\ell C$$ (The path length is 1 cm) 3. The attempt at a solution This is one of my four samples (if you can show me where I'm going wrong with this then I can apply the correction to the others): 2.22 $$\mu$$mol in 1.5ml, therefore there is 0.296 $$\mu$$mol in 0.2ml This info seems to match to the example graph I have. But using the formula above, where $$\varepsilon$$=6.22 for micromol/ml, I get: 6.22 x (0.296/0.2) micromol/ml = 9.2056 This doesn't match up with the graph I have! Any help appreciated! Please!
 Other Sci Sci Advisor P: 1,317 Beer's law is accurate only for values of A from about 0.1 to 1.0. Experimentally, it is difficult to accurately measure absorption values outside this range.
 P: 503 That's the main problem, the results from the example graph are at a maximum of 0.4 for the absorption at 340nm (y-axis) when plotted against amount in micromoles up to 0.4 on the x-axis. I can get a fairly close approximation (the graph itself is supposed to be an estimate) if I use the following formula: (amount in micromoles x amount in ml) x 6.22. But this equation makes no sense; or at least I can't see the reasoning behind it.
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