Rolling, rolling, rolling

[mtnshawn]

Having trouble figuring out the cause of my rolling baseline. The roller is very symmetrical and has a peak to valley time of approx. 10 minutes. Won't bore you w/ the details of my trouble shooting. Any thoughts?
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[Newman768]

When the time between two injections correlates with the baseline rolling time you see a (very) late eluating peak.

[mtnshawn]

the rolling baseline occurs during equilibration as well as during runs.

[Uwe Neue]

How about temperature fluctuations? Air conditioning going off and on? Column heater off/on?

[Newman768]

If the problem is caused by a late eluating peak, you get rid off the problem by flushing the column with high % to 100% organic solvent.
The next equilibrating with your normal mobile phase should show a smooth baseline.
Using a solvent with 10 to 20% less water show such a compound coming from the sample(s) within normal run time.