Register to reply

Beer-Lambert equation

by nobahar
Tags: beerlambert, equation
Share this thread:
nobahar
#1
Jan19-09, 02:45 PM
P: 501
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
[tex]A=\varepsilon\ell C[/tex]
(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 [tex]\mu[/tex]mol in 1.5ml, therefore there is 0.296 [tex]\mu[/tex]mol in 0.2ml
This info seems to match to the example graph I have.
But using the formula above, where [tex]\varepsilon[/tex]=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!
Phys.Org News Partner Science news on Phys.org
'Smart material' chin strap harvests energy from chewing
King Richard III died painfully on battlefield
Capturing ancient Maya sites from both a rat's and a 'bat's eye view'
Ygggdrasil
#2
Jan19-09, 03:54 PM
Other Sci
Sci Advisor
P: 1,400
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.
nobahar
#3
Jan19-09, 05:50 PM
P: 501
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.

Ygggdrasil
#4
Jan19-09, 09:28 PM
Other Sci
Sci Advisor
P: 1,400
Beer-Lambert equation

The slope of the best fit line to the graph should give you ε.


Register to reply

Related Discussions
Beer-Lambert law Quantum Physics 4
Beer-Lambert law question Atomic, Solid State, Comp. Physics 2
Beer-Lambert Law question Chemistry 4
Beer lambert equation and concentration Biology, Chemistry & Other Homework 1
Beer-Lambert Law Chemistry 6