Chromatography Forum

but at the beginning, then when the concentration is bigger, it is more linear. slope of the tangent is increasing instead of decreasing according to increasing concentration. Tt is flat at low concentration and steep at high concentration. Is that due to the active adsorption spots in my non-polar column?

thanks a lot for your time
ziman

That evaluation, the result of adsorption, agrees with the evidence.

best wishes,

Rod

Hi Ziman

You might also have adsorption in the inlet. Try changing or cleaning the liner. What quantity of analyte is in each peak at the low and high end of the calibration ?

Peter

Thank you peter!

the sample is nitroglycerine. The quantity range is from 2e10 to 2e8 g. And the curvature is at the lower end. The column is HP-5ms.

ziman

Thank you too Rod, sorry I did not see your reply at the first glance.

If I have a dirty liner, why do I only have quadratic curve for nitroglycerine, but not for EGDN, which is a very similar compound.

Hi Ziman

You can ask the same question about adsorption on the column.

If I interpet your quantities correctly your calibration runs from 0.2 ng to 20 ng. Your analyte is covered with highly polar nitros, getting the line straight at these levels is not going to be easy. Could you concentrate your samples to get more anayte onto the column ?

Peter

Hi peter,
Yes, we can run more concentrated solutions, but we are interested in this trace amount in real samples.

best
ziman