helium for HPLC -ECD

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Viccroc's picture
helium for HPLC -ECD

Hello everybody!
Going to buy some helium for sparging (ecd method) as we heard that on-line degasser is not good enough to remove all gases. Could somebody please comment on the purity of helium for ECD-HPLC.
We hope that it will improve our CV between injections or will it?
Any recomendations would be greatly appreciated.

Dr. Analytical
Dr. Analytical's picture
If you buy high purity helium

If you buy high purity helium, the same type used for GC with electron capture detection (ECD), you should have no problems.  However, there are some other things you should know about.
You are correct that on-line degassers do not always remove all the gases.  But have you tried them to see if the results are unacceptable?  Depending on the design of the degasser, there may be some ways to improve the results.  What equipment do you have, and what mobile phase will you be using?
Also, be aware that Teflon tubing - the very common tubing used to carry mobile phase from the bottle to the pump - is permeable to air.  So if you have too much tubing after the degassing step, you will still have air in the mobile phase.  To eliminate all air you will have to eliminate all Teflon tubing after the degassing step.  Stainless steel would be a very good choice, but it is expensive.  PEEK tubing should be OK.
Let us know if you have some success.
Thanks for posting your question at scientistsolutions.com

efoconnor's picture
First do no harm.  Get the

First do no harm.  Get the highest purity you can.   Another approach I found very efficeint was to use the LAZAR LAB/ degasser/Filter, Then sparge for 15 minutes.   The Lazar site is http://www.lazarlab.com/hplcsolv.htm.  Works well for electrochemical detection. Less cumbersome than most filtration units and it filters/degasses into the reservoir bottles- just need to order specific caps.
Are you sure the noise is due to outgassing?  Passivation of the pump and metal fluid paths with nitric acid or EDTA may help.
Electronic filtering? 
Polished electrodes?

efoconnor's picture
Sorry, I misread some of the

Sorry, I misread some of the entry.
How bad is the CV?  usually- not always, the gasing may contribute to spikes on your peaks and baseline.  DO you see that?  If not, you may want to resolve the problem to the injection system and not the solvent.  Worn injectors ( stator, rotor or injection needle/pistons, carry over and residua on the column may be the culprit.    Are you sure your pump's check valve or piston are not the source of the error?   What is the CV?  send a sample chromatogram as an attachment.