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Beer Lambert’s Law help..:(

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Beer Lambert’s Law help..:(

Postby TwinkleK » Fri Feb 03, 2012 1:33 pm

Okay, guys need your help soo please help if you can :( :(

I know the equation, I know what to do.. it’s just the units and things.

Here are my concentrations 0.080, 0.040, 0.020, 0.010 and 0.005
I received absorbance readings for these (in 340nm)
Plotted against time (minutes)

Still all cool..

Found the gradient from the graph (mol/min/L)

Now I need to use the “Beer Lambert’s Law” to convert the gradient to velocity using the equation from this law (A= ECL)

(I think I know the steps, but really stuck on the units..but not too sure on the equation calculation anyway)

Please help…
Love, Peace & Freedom..
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Postby JackBean » Fri Feb 03, 2012 4:11 pm

Your concentrations are in mol/l?
What do you mean by gradient?
Instead of mol/min/l use mol/(l.min) or mol/l/min. You may use M instead of mol/l, thus you get M/min (i.e. increase of concentration per minute).
But I guess, what you read from graph is ABS/min, isn't it?
http://www.biolib.cz/en/main/

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Re: Beer Lambert’s Law help..:(

Postby jonmoulton » Fri Feb 03, 2012 4:39 pm

Nice, Jack.

For units, I'd add that you will need the path length for your spectrophotometer and the length unit from your extinction coefficient (hopefully these will match). The most likely light path length though your sample is 1 cm (if the spectrometer/colorimeter uses a 1 cm cell). Extinction coefficients are most commonly reported as 1/(M * cm), so when they are multiplied by a concentration (M) and a path length (cm) they become a unitless absorbtion.
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Re: Beer Lambert’s Law help..:(

Postby TwinkleK » Fri Feb 03, 2012 6:46 pm

The path lenght is 1 cm

The molar extinction co efficient is 6220 l/mol/cm at 340 nm

Stuck :( :(
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Postby canalon » Fri Feb 03, 2012 6:59 pm

So for each of your point you know A (absobance), E (coefficient of absorbance) and L (path length) and you have problem calculating C (concentration)?
I remind you if you put A in Absorbance/min, then C will be expressed in M/min
Patrick

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any proof. (Ashley Montague)
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Re: Beer Lambert’s Law help..:(

Postby TwinkleK » Fri Feb 03, 2012 7:01 pm

Yep, that's it:)

Finding the concentation..the equation has to be arranged. Which I have:)

I'm just not sure of the calculation steps.. (to find C)
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Postby JackBean » Fri Feb 03, 2012 7:39 pm

Oh mein God! What's the problem? :roll:
You have A = e.c.l => c = A/e.l
What's your problem? :roll:
http://www.biolib.cz/en/main/

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Re: Beer Lambert’s Law help..:(

Postby TwinkleK » Fri Feb 03, 2012 7:45 pm

Absorbance: let's say 0.2744 nm
Extinction: 6220 l/mol/cm
Path lenght (L): 1 cm

0.2744 / 62240 = 4.11
(the 1 get's cancelled out)

now what? what's the next step? using international units of enzymes..
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Postby JackBean » Fri Feb 03, 2012 9:56 pm

are you sure you have plotted absorbance(y) against time(x)?

well, nothing, you have concentration and you can do with that whatever you want (I guess calculate some kinetic parameters?)
http://www.biolib.cz/en/main/

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