If you are seeing significant background noise on your detector using a new Cogent HPLC column, it may simply need an initial conditioning to remove any trace residual packing solvents. Flushing the column at a low flow rate overnight with isopropanol, 50/50 isopropanol/DI water, or 50/50 methanol/DI water may be effective.
Another strategy you can try is to run a series of blanks with a gradient method that goes from weakly-eluting conditions to strong conditions. In reversed phase, you might go from 90% aqueous/ 10% organic to 10% aqueous/ 90% organic over 10 min or so.
Evaluate the chromatograms you get from the blanks and see if the UV slope gets flatter with each injection. This may be a good indication that the gradient washings are working.
