[danko]

I am conducting a HPLC analysis, omeprazole in mobile phase: phosphate buffer pH8 (0,05M): ACN (75:25); detector UV 302nm, column Zobax C18, module: Agilent 1100.
The trouble is that the base line tends to increase (about 0,3mAU per 10min). I have replaced the old precolumn but there isn't any improvement. My column is not too old.
Plz tell me all the possible reasons and the solutions. Thank you.

[chiralic]

Maybe you have one of these :

- Contamination of your mobile phase
- Bubbles Air in the detector cell
- Plugged detector outlet line
- Mixer Unit problems
- Retained materials in your column
- Temperature of your column

[danko]

Thank u very much, man. I will check all.
I need more advice...

[Bush]

I am conducting a HPLC analysis, omeprazole in mobile phase: phosphate buffer pH8 (0,05M): ACN (75:25); detector UV 302nm, column Zobax C18, module: Agilent 1100.
The trouble is that the base line tends to increase (about 0,3mAU per 10min). I have replaced the old precolumn but there isn't any improvement. My column is not too old.
Plz tell me all the possible reasons and the solutions. Thank you.

  it's no relationship with your old column, the base line increse only means the concentration of the solution flow through the conductivty detector  has changed!!
  check your instrument to see whether it has leaked first
 then run baseline untill it's base line didn't increse anymore

[profmsg]

before running any sample in mobile phase, you gotta allow the system to settle down. once the system is primed with new mobile phase, allow to run throught the system about 30 minutes and get the stable base line. and run about few trail injections of dissolution solvent and reference standard. this removes all the air bubble present in system if any and also removes if any system parts are contaminated which might be the source. once these conforms that the mobile phase is fine, then only the sample is run throught it.
contamination in mobile phase could be other source if all the these measure didnt work.
do not forget to check the leakage detector whether they are working or not.