October 19, 2020, 11:29:15 PM
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Topic: Enzyme Activity Assay - Can I use the Colorimeter I Have? (Optics)  (Read 514 times)

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Offline anonymous10012

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Thank you for clicking on my post. I am trying to better understand the relationship between absorbance and reflectance (not transmittance). I have included a link to a conversation on researchgate.


I want to measure peroxidase activity of a pretty translucent aqueous extract of horseradish. The colorimeter that I have only measures reflectance (it was purchased for a different purpose).

Can anyone weigh in on whether or not the conversion A=log 1/R would suffice in this application?

Here is another discussion about it. Optics is a weak point for me. Thank you!


Offline Corribus

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Re: Enzyme Activity Assay - Can I use the Colorimeter I Have? (Optics)
« Reply #1 on: November 25, 2019, 10:37:44 AM »
Theoretically you can relate reflectance measurements to absorption measurements. This is frequently done on solid samples using a device called an integrating sphere.


Your problem is that if the reflectance isn't truly diffuse, converting your reflectance to absorbance won't give you a representation of the bulk absorbance properties of your sample. Moreover the reflectance measurement usually needs to be calibrated against a material with a known standard reflectance, presumably to account for sensitivity variations in your instrument.

Could you do this with a handheld reflectance colorimeter? Maybe.... but it's hard to get good absorbance measurements from an integrating sphere, which is intended for this purposes. Because of that, I don't know that I'd trust any absorbance measurement made from a reflectance colorimeter, certainly not a quantitative measurement.

UV Spectrophotometers are cheap and pretty ubiquitous - can't you find one somewhere to use for your measurement?

ALSO: Please don't cross-post.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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