A drifting baseline is a common issue in HPLC. And easily resolved.
Typically, these are the causes:
Change in mobile phase composition. This is the most common cause of baseline drift. If you’re running a gradient, and you’re using a UV-vis detector, you can always expect a drift in the baseline, caused by refractive index effects. Avoid using a steep gradient. Change the mobile phase composition as gradually as possible.
Change in column temperature. Simple. Use a good column oven, even if you’re at room temperature. It’s always a good idea to invest in a reliable column oven.
Mobile phase changeover, from previous injection. You will need to wait for a while, to let the baseline stabilise.
Aging UV lamp. People forget to calibrate and change the UV-vis lamp.
Column bleed. Rarely, the bonded phase may bleed from the column. This is actually quite rare with modern-day bonded columns. If you have a column bleed, you can always tell by the continuously drifting baseline. It will never stabilise, no matter what you do. In this case, you will have to discard the column.
You can avoid column bleed in the first place, by buying a good brand and staying within the pH limit of the column.
Cheers … SKS.