Sine wave on baseline?

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Hello peers,

I am new to ion chromatography and am completely stumped. My baseline on the conductivity detector has gone from straight to creeping upwards with a definite sinusoidal character. Dionex 900 instrument, carbonate/bicarbonate eluent, dilute sulphuric acid regenerate.

Any ideas?

How long have you been running the baseline out? It may be a temperature issue with the cell. How is the Regen working?
Could it be yoir pump? Certain detectors are sensitive to small pulses in pressure. Check you pressure closely. Maybey time to replacd pump seals?
Thanks for the responses My column pressure is pretty erratic. Could pump seals be the cause of that as well? Weird thing is that this happening on 3 instruments right at the same time! Kinda weird for seals to go at the same time, or maybe not. Like I said, I'm a rookie
Hello Again, Mab,

On the 900, leaks would be evident near the pump heads, most likely. Also a place to check for leaks would be near the suppressor. Here's a link to the manual; ... 215-04.pdf

Please refer to pgs. 34-37, and 61-63. I always had the best luck with syringe priming. Best Wishes!
If the same symptom is showing up on three systems at the same time, that suggests an environmental variable. The most likely (especially with conductivity detection) is temperature. If this were my problem, I would check to see if the fluctuations are correlated (i.e. have about the same period) on the three systems. If so, I would get a thermocouple and recorder and track the temperature on one of the systems.

Another (much less likely) cause would be fluctuations in the mains voltage.
-- Tom Jupille
LC Resources / Separation Science Associates
+ 1 (925) 297-5374
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