Calculate concentration

Basic questions from students; resources for projects and reports.

12 posts Page 1 of 1
Hello,

Does anyone know how calculate the concentration from a gc/ms chromatogram which is having retention time and peak area only? I don't have any internal standard.Thank you
To *grossly* oversimplify: you run "calibrator" standards at known concentrations (ideally at 5 levels) and plot peak area vs. concentration. If all goes well, you will see a linear relationship; the slope of the best-fit straight line is the response factor (RF). Now run your sample(s); divide the peak area by the response factor to determine concentration.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
i don't have 'calibrator' standard of known concentration. i only have peak area and retention time.
Then your screwed. You must have an pure internal standard for calibration since the detector response/mass can vary radically between molecules.
snhafizai wrote:
i don't have 'calibrator' standard of known concentration. i only have peak area and retention time.


Depending what accuracy you need you might be able to calibrate using a similar compound. What compound is it that you want to quantify ?

The more you tell us the more we can help you.

Peter
Peter Apps
Hi, i want to quantify the dibenzothiophene (DBT). the initial concentration was assumed 500ppm but i need to calculate the actual concentration of the initial sample in order to get concentration of DBT after the adsorption process. thank you
Dibenzothiophene is readily available at high purity in small quantities - just buy a standard. Sigma-Aldrich have it, or probably others.

Peter
Peter Apps
Is there any other option to calculate concentration since i already finish doing the lab works? Thank you.
No. You must calibrate your instrument with a known concentration of the analyte before you run your analysis to determine an unknown. As Peter mentioned, you can use a similar material if you want to get close but you won't know for sure, exactly, unless you use the authentic material to calibrate.
snhafizai wrote:
Is there any other option to calculate concentration since i already finish doing the lab works? Thank you.


No, you should have run the calibration when you had the chance I'm afraid. The best you can do now is to compare between samples, e.g. before and after they have been through the reactor (assuming that you ran both before and after samples).

Peter
Peter Apps
I already compare the result before and after they go through the reactor. However the results vary and i think the initial concentration that i' ve prepared is above 500 ppm.
Measuring the concentration of the feed will not make any difference to the variability of the results.

Peter
Peter Apps
12 posts Page 1 of 1

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