beerlambert law
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 Garter
 Posts: 4
 Joined: Thu Feb 26, 2009 3:48 pm
beerlambert law
hi, im tryin to find out the concentration in micro mol/min
I possess the absorbance (0.106) and the extinction coefficient is 6.22x10 to the power 3 l.mol 1 . cm1
the distance of travel is 1 cm
i beleive the equation to be C = absorbtion /(epsilon x l)
Is it as simple as putting the results into the equation, or will i have to change units
i couldnt find any examples that found the concentration for micromol/min
any tips would be greatly appreciated xx
I possess the absorbance (0.106) and the extinction coefficient is 6.22x10 to the power 3 l.mol 1 . cm1
the distance of travel is 1 cm
i beleive the equation to be C = absorbtion /(epsilon x l)
Is it as simple as putting the results into the equation, or will i have to change units
i couldnt find any examples that found the concentration for micromol/min
any tips would be greatly appreciated xx
 jonmoulton
 Viper
 Posts: 442
 Joined: Fri Feb 15, 2008 5:38 pm
 Location: Philomath, Oregon, USA
Re: beerlambert law
micro mol/min is not a unit of concentration  it is a unit of concentration per time. You can use the Beerlambert law to get the concentration, but you will need to consider the design of the experiment to figure out how to combine your concentration data with a perminute factor. You are likely looking at several measurements of concentration performed at different time points. Convert each absorbance to a concentration, then think about the time factor.

 Garter
 Posts: 4
 Joined: Thu Feb 26, 2009 3:48 pm
Re: beerlambert law
The reading i have for absorbance is the change in absorbance over 1 minute, so do i just simply find the concentration, and becasue the absorbtion is already expressed as per minute.
are all the unit i have compatible to enter straight into the equation? thanks
are all the unit i have compatible to enter straight into the equation? thanks
 jonmoulton
 Viper
 Posts: 442
 Joined: Fri Feb 15, 2008 5:38 pm
 Location: Philomath, Oregon, USA
Re: beerlambert law
I expect the units of the molar absorptivity to be M^1 * cm^1. This will give you an answer in molarity. You'll need to convert to micromoles.
Watch out for the unit mol  I interpret that as moles. Concentration is mol/l or M. You gave the units of the molar absorptivity as l.mol 1 . cm1, which I would choose to write M^1 * cm^1, but these are the same.
I made a mistake in my last post when I wrote "micro mol/min is not a unit of concentration  it is a unit of concentration per time". I should have identified microM/min as the unit of concentration over time. You must associate a unit of volume with the moles to make it a unit of concentration (and M is defined as mol/l).
Your units on the molar absorptivity do correctly have the volume unit (l * mol^1 * cm^1 = M^1 * cm^1) and applying this in the BeerLambert equation will give units of molarity (M):
C = absorbtion /(epsilon x l) with units 1/((M^1 * cm^1)*cm) = M
Since you have readings 1 minute apart, you can take the difference in the concentrations (M) and the difference will be in M/min. If your reaction is occurring in 1 liter, you can treat this as mol/min. You'll need to convert to microM.
Watch out for the unit mol  I interpret that as moles. Concentration is mol/l or M. You gave the units of the molar absorptivity as l.mol 1 . cm1, which I would choose to write M^1 * cm^1, but these are the same.
I made a mistake in my last post when I wrote "micro mol/min is not a unit of concentration  it is a unit of concentration per time". I should have identified microM/min as the unit of concentration over time. You must associate a unit of volume with the moles to make it a unit of concentration (and M is defined as mol/l).
Your units on the molar absorptivity do correctly have the volume unit (l * mol^1 * cm^1 = M^1 * cm^1) and applying this in the BeerLambert equation will give units of molarity (M):
C = absorbtion /(epsilon x l) with units 1/((M^1 * cm^1)*cm) = M
Since you have readings 1 minute apart, you can take the difference in the concentrations (M) and the difference will be in M/min. If your reaction is occurring in 1 liter, you can treat this as mol/min. You'll need to convert to microM.

 Garter
 Posts: 4
 Joined: Thu Feb 26, 2009 3:48 pm
Re: beerlambert law
thankyou for your help. ive manages to complete the question now
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