problem with eluent generation

[lpalme02]

Hi

I'm running carbohydrate analysis using a KOH eluent generator cartridge and have been getting an annoying baseline step of 3 to 4 nC at about 20 to 30 minutes after the last change in eluent concentration. I run the system isocratically at 10mM for 18 min with a 100mM column regen for 4 minutes directly after each run. This step has been forcing me to run a long re-equilibration step (~18min) and the baseline still isn’t flat after the step as it continues to rise gradually. I have looked at papers and dionex technical notes and this baseline change doesn’t seem correct. Can anyone help me with my problem?

Thanks

Lachlan

[JMadden]

Are you running the EG degasser in vacuum mode? The Eluent Generator Cartridge generates a lot of hydrogen gas as a byproduct of the electrolytic reaction. Hydrogen gas is electrolytically active and will cause a baseline shift on an ED. A vaccum degas for the EG is much more effective at removing this gas than the static degasser that ships with an EG; it eliminates a lot of baseline disturbances. Dionex sells a vacuum add-on kit that connects to the degas pump in your system pump.

[lpalme02]

Hi John
thanks for the info but we already have a vacuum degas unit installed.
the base line step only occurs when there has been a change in eluent concentration, when i run isocratically there is no step. i have been trying some isocratic runs (10mM NaOH) and when there is no injection (ie blank) the baseline is flat, but when i inject milliQ i get 3 dips at 7.2, 17.3 and 18.1 and after the last dip the base line is ~1nC higher than before the second dip. i also get a shallow dip much later (>20 min) which i assume is the oxygen dip.