Fluctuating baseline

[hplcnewuser1]

Hi I switched a new column and guard-column and cannot get a steady baseline. What should I do to get a flat baseline. Right now it fluctuates between -5 and +5.
Ruled out lamp, detector and flow cell, baseline is steady at 0 flow. mp's are the same as old column.So it has to be something with new column. Pressure does fluctuate at lower flow rates but is steadier at 1ml/min or higher
Thanks for any help.

[Gerhard Kratz]

Check out your column connections. Maybe there is an extra dead colume, called extra column effect. Check also for leaks. Remember, your column cannot move or twist by its own.

[tom jupille]

Is the "fluctuation" cyclical or random? If it's cyclical, check to see if it synchronizes withe pressure trace. If it does, look for a leaky check valve.

[James_Ball]

We just had one instrument that had a saw tooth pressure fluctuation of about 1 to 1.5 bar and similar fluctuation in the baseline and reseating the connections and ferrules solved the problem. Apparently it was leaking the tiniest amount because it wasn't completely sealing, though you could not detect any leak at the connections. So recheck all of your connections to make sure they are seated well and replace any ferrules that may be questionable.

[hplcnewuser1]

thanks for replies. I'm using water and ACN as mp's. have a not working degasser so that might be causing some of the trouble. this non cyclic baseline fluctuation happens only with one particular column that is brand new. no baseline fluctuation with old columns.
pressure does fluctuates +/-8bar but that might be due to small air in pump because of solvents non being degassed i think.
ps. i did try to add guard-column to this column and i my have made too long conection of ferule to tube and damaged the column in the process... i idk
also analysing a very sticky substance so it might have already clogged the column.

[James_Ball]

That is quite a bit of pressure fluctuation and is probably because of the bad degasser. If you have a large enough ultra sonic bath try sonicating the mobile phases to remove dissolved gasses and see if that helps. You can also vacuum filter the mobile phases and let the vacuum pull on it while shaking it to help degass also.