June 13, 2021, 09:42:14 AM
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Topic: How to calculate the concentration of a compund using chromatography  (Read 203 times)

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Offline old_dog_learning_new_trks

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Hello,

I am so sorry for such a newbie question.  I am a retired person trying to learn chemistry during the pandemic, and I need some help.  I am trying to figure out how to do a basic calculation for chromatography.

If I take a sample of something/anything, that weighs 5 grams, and I put it in a solvent, lets say it is 50 ml.  I pipette off 2 ml of that and inject it into a liquid chromatograph.  Obviously I would need to have already done a calibration on the liquid chromatograph, and I would have integrated peaks along the way to get that calibration.  But if I run that sample, and I get a peak that I integrate - how do I calculate the concentration in that 5 gram sample?

I get that I have the area of the peak, and I compare it to the calibration peaks - but how do you account for the size of the sample, the volume of the solvent, and use that to figure the concentration?

Thank you for anyone who is willing to take the time to explain!
« Last Edit: April 17, 2021, 09:12:02 PM by old_dog_learning_new_trks »

Offline Orcio_Dojek

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Quote
how do I calculate the concentration in that 2.5 gram sample?
I would rather calculate concentration in 5 g, as 5 g is mass of sample you wrote earlier.

If chromatopgraph gives results in mol / liter, concentration in sample (mole / 5 g of sample) will be 1 / 20 (50 / 100) of given result.

If it gives results in grams (grams in 2 ml sample), concentration in sample (grams / 5 g of sample) will be 25 (50 ml / 2 ml) times higher than given result.
« Last Edit: April 17, 2021, 07:05:12 PM by Orcio_Dojek »

Offline old_dog_learning_new_trks

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Re: How to calculate the concentration of a compund using chromatography
« Reply #2 on: April 17, 2021, 09:13:02 PM »
Thank you Orcio, I appreciate you explaining that to me.  I am going to try to work that out.....stay tuned! I will let you know how it goes.

Offline jeffmoonchop

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Re: How to calculate the concentration of a compund using chromatography
« Reply #3 on: April 17, 2021, 10:43:04 PM »
Your calibration will tell you the result. If you have 5 calibration points of known concentration with peak areas 100, 200, 300, 400, 500 and your unknown sample has a peak area of 250, you can calculate the concentration easily by drawing a graph.

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