Using calibration curve fits to quantitate

Chromatography Forum: GC Archives: Using calibration curve fits to quantitate
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Stephanie on Friday, August 13, 2004 - 02:39 pm:

I am relatively new to the world of GC and am currently trying to determine the linearity of our method using ECD. After running a series of standards, I find that the instrument does not actually calculate the amount of the standards which are higher than the highest one used in the calibration curve. I am using an agilent 6890, with quadratic fit. Is it typical under these circumstances that a calculated amount is not given if the area count is higher than that of the highest calibration standard? I ran a similar set of experiments with the FID and did not encounter this problem at 5x the concentration of the highest calibration standard.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By carla on Sunday, August 15, 2004 - 02:28 pm:

Extrapolate your cal-curves isnt allowed. Maybe with a linear curve fit, but with quadratic fit? How should that work?
I dont think that you got good results with the FID, if your curve was also a quadratic.
Try to run a two-point calibration and tell the software: "quadratic curve fit", its the same, it doesnt work.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Manuel on Monday, August 16, 2004 - 04:42 am:

In the case of ECD it is well-known that this Detector isn't linear over a wide concentration range ! Using the ECD you must calibrate at a lower range of concentration and strictly not extrapolate your cal-curve ! Then you can use a linear fit in software !


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Stephanie on Monday, August 16, 2004 - 11:28 am:

Well, that is what I figured...just needed confirmation. Looks like the analysis just got that much more difficult.


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