Base line problem using ion pair reagent

[maygo]

I am trying to work with a method that had a great baseline during for months, and now has a bad baseline. I would call the base line wavy, but that would imply that it is regular.

The method uses 1-octanesulfonic acid sodium salt in the mobile phase, and a C18 column. I have used more than one column, different lots of the ion pair, and even different LC's, but the problem is still following me.

Any suggestions on how to get my good baseline back?

Could the temperature at 40 deg C be part of the problem?

[John Dolan]

Is the baseline change immediate or after the column/mobile phase have been in use for some time? This may simply be a matter of strongly retained junk building up on the column over time, then bleeding off. Try flushing the column with strong solvent (MeOH) and then go back to your normal mobile phase to see if that quiets things down. The temperature shouldn't be a problem. - John

[Kostas Petritis]

Maygo,

Do you imply that the regulation at 40 C is what changed between the method that worked ((no baseline problem) and now (base line problem)?

If your column temperature control system does not do a good job (i.e. it heats at 40 +/-5 C) then you might have distrurbed equilibrium of your column dynamic modification, leading to increased amounts of ion-pairing eluting out of the column when the temperature increases (i.e. 45 C), then decreasing as the column tries to re-equilibrate at lower temperatures (i.e. 35 C) leading to the "wavy" baseline...

[Mark Tracy]

Have hou checked your water source?

[pharmason]

i dont think temperature is creating any problem if it is stable or with in a given range,but most of the time problem with C18 column is washing after use u should try washing it with 50;50(organic:diwate) for a 10 colume volume atlest after use and store c18 column in 80:10(organic:diwater) , and when u start your run make sure u give some equilebrium time for column, hope this will work out
Avi patel

[maygo]

I had cleaned my column and system for hours before and after use to see if that could clear up the problem.

I ended up switching to a different type of LC and (using the same column, mobile phase, and parameters) the baseline was fine.

Either I had been on two LC's that needed further cleaning, or there is enough of a difference between a Water's Alliance, and an HP Agilent to cause the baseline to clear up.

One other possibility is that the Alliances have their detectors on top of the systems with the Air Conditioning blowing on them, while the Agilents have their detectors on the bottom with the lines better shielded from temperature changes.

If I have time, I will run on an Agilent with the tubing going into the detector protected from drafts.