problem with peak moving through chromatogram

[Vladimir Stankov]

Hi everyone!

I have problem that in two same analysis (same mobile phase, column ...)my standard (example melamine) has two different retention times. I'm using Thermo's MS spectrometer. Is retention time important when i use MS detector and what can be the problem about different retention time?

Thanks very much!

[mehcp]

I am not sure if this applies specifically to your applications, but I wonder if this may be due to ghost peaks or wrap-around peaks. Ghost peaks can occur when a column irreversibly binds material, and then releases small amounts the remnant with subsequent injections. Wrap-around peaks can occur when the elution conditions are not strong enough or long enough to elute an analyte, thus they come out in the following run at a specific point in the gradient.