By Anonymous on Wednesday, January 16, 2002 - 06:38 am:
I have a problem with a negative peak in my chromatogram. The negative peak appears after appr. 11 min. The mobile phase is a mixture of acetonitrile/water/tetrahydrofurane and the method is a gradient method with a shift in composition after 2 min. and after 49 min.
The peak is in both suitability solution, samples and blinds and appears with different batches of acetonitrile and tetrahydrofurane.
By Anonymous on Wednesday, January 16, 2002 - 12:33 pm:
You don't give much information to go on, not even the type of detector you're using. A change in refractive index sometimes causes a negative peak in a UV detector. Sometimes a negative peak will result from a sample solvent that is more pure than the mobile phase.
Without knowing more about your system, I don't know what I could add.
By Uwe Neue on Wednesday, January 16, 2002 - 05:02 pm:
Peaks in gradients are often due to soemthing in the water. Change the equilibration time with the initial composition of the mobile phase. If the peak increases with increased equilibration time, it is somewhere in your starting mobile phase.
By Anonymous on Tuesday, January 22, 2002 - 06:44 pm:
Go look at the series of threads on ghost peaks above. The culprit was dissolved air. If the mobile phase has more dissolved air than the sample the peak would be negative.
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