slowly decreasing baseline

[John]

I have a baseline that is dropping by about 1mAU per 10 min. I have removed the column, washed with MeOH and water to no avail. The gradient of drop is proportional to flow rate and. The gradient of drop also decreases with wavelength. The baseline levels when the pump is switched off. The baseline drop is perfectly linear. This is a brand new system. Any thoughts?
J

[Mark Tracy]

New HPLC pumps sometimes have trace contaminants in them, not enough to flunk the factory QC, just enough to be an annoyance. Try leaving it running at a low flow over night and see if it flushes clean. (Once I got TFA into a PEEK pump and it took all weekend to get it out.)

[ym3142]

I think if this drifting happened under no column, then the LC was not stable or clean;
if this drifting only happened with column but not without column, then the column may not stable or clean.

[DR]

If the MP hasn't been degassed for a while, sparge it.

If there's any TEA in the MP, just pull ~100mL of the MP, add a little more TEA to it and let it recirculate that overnight (column equilibration).

[John]

I think it is contam in the detector. Cleaned overnight with IPA and water. Acceptable now. Annoying thing to happen on a brand new LC.
This is a Shimadzu Prominence, has anyone else had this problem?

Thanks for your help.
J

[Mark Tracy]

Yes. Not specifically Shimadzu. Hewlett-Packard (prior to becoming Agilent) had some real bad factory QC problems for a while. They eventually tightened up their operation.

Complain to your sales rep. If enough people have the same problem, they will get the message sooner or later.

[tx]

Do you have more than one pump (chanel)? If yes, put all chanels into one bottle of MP and try baseline again.