Check the detector with the mobile phase without the column.
Dear Wael
In order to answer your question you need to specify what sort of pump you are using. Most HPLC pumps do have a slight pulse at such low flow rates which will be seen as regular jaggedness in you baseline. UPLC pumps can easily handle such low flow rates without pulsing because they they operate at much higher pressures.
I also agree that the detector may be the cause. It could be of the detector sensitivity and your are seeing the electronic noise or there may a small bubble trapped in die flow cell which with also cause an unstable baseline. However, if the baseline have been creeping up this could be, due to the low flow rate, that something is slowly leaching off you column.
Hope it helps.
Marina
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