I've been having a BIG problem with a system peak which comes out right on top of my dopamine peak. I am using an Antec Decade ECD with a C18 150 x 2mm Hypersil column. Having read many similar problems on this website it seems that dissolved oxygen can be a serious culprit. However most users are using UV detection. Can dissolved oxygen also be a possible reason for my problem even though I am using an electrochemical detector? I do have an in-line vacuum degasser so the MP is degassed but the samples are not. The samples I have are only 40ul in volume so degassing them will be a most interesting proposition!

I really hope someone can help me as I have changed (systematically) pretty much everything I can think of e.g. MP, column, autosampler (disconnected to allow manual injection) the flow cell, eluted water that has been put down an identical column in an attempt to remove the "contaminant"

I look forward to hearing from people

nick

Nick,

I think the first thing I would do is to inject a blank solvent prep without your analyte of interest and see if the spurious peak is still there. That would be a good indication of dissolved oxygen in the sample prep. If this is the problem maybe degassing the solvents prior to sample prep might help?

Regards,
Mark

Thanks Mark,

I did that and it was there so I believe that is the case. Having trawled through many questions on this website I found one suggesting that temp change would alter the solubility of air bubbles and hence move the peaks - I tried this on Friday afternoon (decreased temp from 35 degrees to 25 degrees) and it seemed to remove the problem. I hope it stays away!

nick

Nick:
You can do several additional things to minimize that interference.
(1) Use a different type C18 column.
(2) Use a full loop injection. Some automatic injectors place an air bubble before and after the sample segment in the partial loop mode.
(3) Install a piece of low dead volume gas-permeable tubing between column and detector. For example: a "knitted" reaction coil made of PTFE.
(4) Use your mobile phase in the last dilution step.
(5) Generate a hydrodynamic voltammogram of dopamine and the system peak. You may be able to find a potential with good enough sensitivity for dopamine and much smaller size of the system peak.

Petr Jandik