Chromatography Forum

I have a slight basline drift with my basline drifting about 0.0005 AU over 1 min...is that normal?.....i would like to get it too no drift. Im using the following method below with a graident. What can i do to improve the drift?. I have just replaced the lamp and the column
Eluent: Mobile Phase A – 100% Organic free water

Mobile Phase B – 100% Methanol

Gradient:

Time
(min) Flow
(mL/min) %A %B Curve

Initial 0.500 69 31 -
4.00
0.500 69 31 6
9.00
0.500 40 60 8
10.00
0.500 40 60 8
10.10
0.500 69 31 8
12.00
0.500 69 31 8

What kind of detector are you using? I've got 20+ year old Waters 486 detectors that make <.0001 AU/hr and you are running 0.03AU/hr. Every detector I have used has a recommended flow cell cleaning procedure to follow. Flushing the cell with weak things like Nitric Acid, THF, IPA may help (may have to let them sit in the cell for awhile). Are you controlling the temperature of you column? You may be seeing temperature drift if not. Could be as simple as air in your detector. Try flushing it out at a high flow rate (take off your column first)!

PDA detector.....i already did the flow cell clean using phosphoric acid. im now seeing if it is the pumps by isolating each pump and seeing if the drift happens with both when individually selected. Could it just be cause im running a gradient with water and methanol?

Ok tryed pump A...drift....tryed pump B...drift. Turned off both pumps and there was still drift!!....so therefore its not the pumps so what can it be?

When running a gradient from water to methanol you may see for sure a baseline drift depending on the detection wavelength. UV absorptions may be quite different for these two solvents.
When trying to measure the drift of the detector alone (i.e. with pumps off) be sure to first thoroughly equillibrate the flow cell with eluent.
Other possibility: temperature. Are you using a column oven? Is there an air-condition nearby?

yeah i kinda new that about the methanol and water...temperture maybe be an issue but maybe not so much....im gonna run today ..............its a gradual gradient which will push the baseline in the opposite direction so i kinda hope it balances out. I did equilbrate the system for long time before turning off the detector to monitor the baseline and it still drifted so what im thinking is that the flow cell maybe dirty so maybe i need to remove and have a look at it...any other sugesstions...thanks for your replies

another thing i forgot to add was no PM has been performed on the UPLC for 18 months...might be the reson im having so many issues!!