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Absorbance

Definition

noun

(analytical chemistry)

A logarithmic measure of the amount of light absorbed (at particular wavelength) as the light passes through a sample or substance.

(microbiology)

The measure of the amount of light absorbed by a suspension of bacterial cells or a solution of an organic molecule with the use of a colorimeter or spectrophotometer.


Supplement

Absorbance measurements are often carried out in analytical chemistry, since the absorbance of a sample is proportional to the thickness of the sample and the concentration of the absorbing species in the sample.

Absorbance may be applied in plotting the growth of bacteria in suspension cultures. It may also be used in gauging the purity and concentration of molecules (e.g. proteins) in solution.

Although absorbance does not have true units, it is quite often reported in "Absorbance Units" or AU.


Word origin: L absorbére, equiv. to ab- + sorbére to suck in, swallow + -ance.

Related forms: absorbency (noun).

Synonym: optical density.
Compare: absorption.


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blank and substrate control give OD reads

I'd check each component of the reaction mix separately for absorbance against water. BTW shouldn't your blank have absorbance 0?

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by JackBean
Mon Jan 20, 2014 10:55 am
 
Forum: Molecular Biology
Topic: blank and substrate control give OD reads
Replies: 9
Views: 3153

Re: blank and substrate control give OD reads

You centrifuge the reactions in the 96-well plate and then in that you measure absorbance? How can you do that if the bottom is blocked by your substrate? Can you describe your reactions and controls in more detail including some example absorbances so we can make ...

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by intandiana
Sun Jan 19, 2014 5:57 am
 
Forum: Molecular Biology
Topic: blank and substrate control give OD reads
Replies: 9
Views: 3153

Re: blank and substrate control give OD reads

You centrifuge the reactions in the 96-well plate and then in that you measure absorbance? How can you do that if the bottom is blocked by your substrate? Can you describe your reactions and controls in more detail including some example absorbances so we can make ...

See entire post
by JackBean
Fri Jan 17, 2014 10:05 am
 
Forum: Molecular Biology
Topic: blank and substrate control give OD reads
Replies: 9
Views: 3153

pka

Hey, :) need help working this out: pH: 4 molar extinction coefficient: 0.0187142857 m-1cm-1 absorbance at 500nm: 1.492 [Acid form]?? (work out using molar extinction coefficient) [base form]? lg([acid]/[base])? pKa? If someone can guide me on how to do this especially ...

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by 2468
Fri Nov 30, 2012 10:45 pm
 
Forum: General Discussion
Topic: pka
Replies: 6
Views: 3231

Can particle size affect spectrophotometry?

... put this...doesn't seem to fit anywhere else. But if you have a lipid sample in a cuvette, I know that changing the concentration will affect the absorbance readings. But what about particle size? For example, I was working with two different lipids (phosphatidylcholine and phsophatidylglycerol). ...

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by keetner
Thu Nov 29, 2012 3:24 am
 
Forum: General Discussion
Topic: Can particle size affect spectrophotometry?
Replies: 1
Views: 1088
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