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Molar Extinction CoefficientModerator: BioTeam
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Molar Extinction CoefficientHi.
Please can someone help me here, as I am confused and I don't want to end up more confused! Thanks in advance! The extinction coefficient is present in the beerlambert law (A=ECL). However, how would I calculate the extinction coefficient from a graph where concentration is on the xaxis and optical density on the yaxis? Would I have to work out a gradient? And so, where do I go next to work out the extinction coefficient?? I've tried reading up on the extiction coefficient but I don't seem to find anything which would help me work the extiction coefficient from a graph. Thankss!!
Hi there
If you solve Beer's law for E you get = A/cl In your graph you have c on the xaxis, and A is on the yaxis So the slope of your line (rise over run) is A / c You'll have to compensate if you've used a path length besides 1cm, otherwise you can ignore l. If your c on the xaxis is in molar, then your units for E are M1 You can then take any given A reading, divide by E, and get M You can also calculate the extinction coefficient if you can find it check out Protein Science (1995) 4:24112423; Pace et al "How to measure and predict the molar adsorption coefficient of a protein". Good luck!
omg:
A = ecl with e = molar extinction coefficient, c = concentration and l = length of the light through the sample to calculate e you chose on the xaxis the concentration and on the yaxis the absorbance/extinction or whatever you call it. > than the slope of that grapgh will be equal to delta y/delta x = A/c = e*l > thus your slope in the curve is equal to 2 constants: the molar extinction coefficient and the path of the light through the sample > e * l
not true: absorbance/extinction has no unit (because it is also equal to I/I(0) > intensity transmitted/blanc transmittance), thus when c in molarity and l in cm, than the molar extinction coefficient will have the unist M^1 * cm^1
Re: Molar Extinction CoefficientSo if I have this data:
Absorbance _at_ 405nm: .875 Concentration (M) of Cr(NO3)3 (aq): .25M Since you're saying that if l = 1cm (standard curvette), then E = A/C so then: .875/.25 = E E = 3.5?
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