Chromatography Forum

I'm using a Dionex Ion Chromatography system and have just started having jagged sulfate peaks. I'm using their Seven anion standard and an AS4A column with carbonate eluent. I've been using this system for years and years and have never seen this. I've swapped out the column and that made no difference. Nor did new eluent and standard prep. I'm really curious as to why it's only on the 7th peak? Retention time and % Recovery are consistent. Any suggestions?

Hi JHoward333, please e-mail me your Chromeleon backup file (CMB) containing the affected sequences and we'll take a look at it (cannot make a conclusion from your description).

In the meantime,
What does your blank injection look like (running same PGM)?
Have you tried a different 7 anion standard from a different lot #?
Any other changes in the inline consumables (suppressor, etc.)?

Update for our Chromforum colleagues: after reviewing the chromatograms, the background anion conductivity trace showed even pulsation pattern (~0.2 min baseline width/pulse @ 2.0 mL/min, ~0.1 uS intensity/pulse).



Moreover, the chromatogram of the 7 anion standards injection showed for sulfate and phosphate the baseline pulsation that rode on the upslope/downslope of the analyte peaks and gave a bumpy pattern at the peak apexes. Good RT and injection area reproducibility reported.



Conclusion: most likely a sticky check valve for this DX-500 pump. Last PM was approximately a year ago. The blank conductivity trace looks like a classical pump pulsation effect from a malfunctioning/worn check valve. There are of course other possibilities ...JHoward333 will perform a PM on the pump and report back to us. Good luck!

Thanks, John! Our conversations have been most helpful. I will perform the maintenance this week and will post how things go. Thank you for the suggestions.