Hello Everybody
I am using HPLC with ELSD to determine the unknown concentration of my samples after adsorption test.
My samples contain a blend of two surfactants so i tried to prepare two calibration curves for the two surfactants.
One of the calibration curves is linear where the other one doesn't seem to be linear so is it possible to use any other type of mathematical functions. Or is there any other way to solve this problem. "the Excel file is attached"
Just to add an extra comment: i prepared the preparation of the samples twice to make sure because that's what i was advised to do and i repeated the calibration curve twice and i checked the repetition of the same samples and there were no significant difference.
Your help is highly appreciated.
Regards,
Mr. Belhaj,
Excel does not represent suitable professional software for statistics.
Thank you Dr.Ivanova for your reply.
It's the same but i extracted the data to excel in case someone would request it.
I have now the standard curve of the first surfactant it looks the same.
Dear Sir. Concerning your issue about the standard Curve for a mixture of surfactants using HPLC . I think the following below links may help you in your issue:
https://www.lgcgroup.com/LGCGroup/media/PDFs/Our%20science/NMI%20landing%20page/Publications%20and%20resources/Guides/Calibration-curve-guide.pdf
http://lab-training.com/2013/01/03/how-to-make-a-calibration-curve-and-calculate-sample-concentrations-using-excel-video-tutorial/
https://terpconnect.umd.edu/~toh/models/CalibrationCurve.html
Thanks
We had to develop polynomial calibration curves while using an ELSD. Look at the huge difference in area counts between your linear and none linear surfactants. First thing I would try is to cut the concentration of the non linear surfactant run.
Noel W Davies
Thank you prof Noel for your comment it's highly appreciated.
Please check the attached file do you think this is acceptable.
Yes i tried to repeat the analysis of some concentrations just to check the repetition of the instrument and there were no significant difference. You can check the file attached.
So what do you recommend prof? Should i have more points for each concentration.
The trouble with ELSD is that in most of all cases the dynamic range the detector provides consists of a series or non linear sections (a.k.a sigmoidal, see Michael Toner's comment above).
It is not only the fact that it is non linear, but you will have to decide when to use which calibration function. One of our colleagues already stated the need of a polynomic calibration function.
First of all: Nothing wrong with polynoms, if they are statistically proven the correct calibration functions.
Second: It is difficult to justify the extended calibration work - under daily conditions - in addition to the extended post analytical data evaluation.
If you (have to) work with ELSD, one possible strategy is to limit the calibrated range so that you find a "simpler" calibration function. This on the other hand gives away the benefit a digital ("autoranging") detector provides. I assume that this is the case in your lab.
Just in case: If you have the chance to look into another "universal" detector, try looking into a Corona CAD. Still not linear responses, but you get along with second order calibrations very well.
Hope this helps a bit.
Best regards,
Detlef.
Is it possible to have two calibration curves for the same surfactant one for low concentrations and the other for higher concentrations.
Ahmed Belhaj, I think you have to. None of the correlations (including a third order polynom) I tested did improve the fit. In addition, the correlation coefficient of 0,97 for the lower concentration indicates that the correlation between area and concentration is not the best and four calibration levels might not be sufficient. Only as a suggestion, or food for thought: What about adding one or two extra levels for both ranges?
Thank you for your suggestion i will try to add more levels for each range.
I would try different temperatures and/or gas flow to see any improvement.
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