peak inverted

[fredj]

Hi everybody
I was using the same conditions and the same method to separate two stand mixture suddenly the chromatogram profile was inverted: the first peak appear in the second position and the second appear in the first position... what can be the reason for that?

[Peter Apps]

It would be helpful if you could post the chromatograms - instructions are in a sticky at the top of the page.

Peter

[naythewave]

If you are sure that your MF is done right, than your main suspect I would say is the column...

[tom jupille]

Depending on the robustness of the method, it could slso be a temperature or a pH problem.

And, are you sure about the identities of the peaks and of the detection wavelength?

[fredj]

I had a problem with my sample so this is why I've seen that...
thinks for your help

[Peter Apps]

Hi Fred

I am glad that your problem is solved but I am still not sure what it was you saw -

you used to have two peaks, when you had the problem you still had two peaks but the peak that used to come out first came out second and the peak that used to come out second came out first, in other words the peaks swapped retention times - yes ?

Were you recognising the peaks on the basis of their size and/or shape by any chance ? If so, then the problem becomes that the peak that used to be the bigger of the two is now the smaller of the two, and the peak that used to be the smaller is now the bigger. This is a lot easier to explain than two peaks swapping position to each other's retention times - the composition of the sample had changed.

Peter