baseline increase at the start of the gradient

Hello All,

I am experiencing a huge baseline increase issue during my plasma metabolome analysis exp.

The BPC traces are as follows ( in both list and overlay modes) 

It is supposed to be separated like the K13 sample (second from top) but somehow it starts to be broadened and not separeted in most of the samples.

The sample(s) are methanol extracted plasma (5 ul injection volume).

I initially suspected column overlading but dilution did not help.

The second thought was the that the jump from A% to B% was steep and I have also slightly added a 4 mins isocratic step again not much improvement.

The only thing I have not tried is to increase the gradient time from 23 mins to sth like 40-50 mins. But this also does not make sense to me as the column is HSST3 (1.8 um, 50 mm, 2.1 mm) 

Any possible solution or suggestions?

Thanks in advance,

Basri

Parents
  • Basri-

    You might try making your sample solvent match the starting mobile phase and see if that helps.

    A 1-2 minute hold at 99% A at the beginning of the run may help a little.

    What major ions are associated with the raised signal and the beginning of the run and do they form chromatographic peaks (check out the EIC of some of the more intense ions).

Reply
  • Basri-

    You might try making your sample solvent match the starting mobile phase and see if that helps.

    A 1-2 minute hold at 99% A at the beginning of the run may help a little.

    What major ions are associated with the raised signal and the beginning of the run and do they form chromatographic peaks (check out the EIC of some of the more intense ions).

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