Chromatography Forum

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

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.

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.