Inconsistantly baseline jumps

[ivarg]

Hi
I have a problem with inconsistantly baseline jumps. They appear in some chromatogram and one or more times in each of those. Also could be in just one out of 5 from same sample. This problem appeared after at least two years of using same method and equipment. The sample is one pure compound, gradient with 55% (to 70) methanol and 45% citrate buffer (adjusted with 10% KOH) mixed online. C18.



Anyone experienced something similar? And might have an answer?
Thanks i advance
Ivar

[nschwartz]

What does your chromatogram normally look like? What detector is this? I'd say it looks like it might be bubbles in your flowcell, but hard to tell without a basis for comparison. Are your retention times moving around any?

[ivarg]

Hi nschwartz

The normal chromatogram, would be with just the peek at the dotted line situated no 3 from right. I don't have a chromatogram now, but I can get one on monday. The retention time remain as before. I have a shimadzu spd pda (the whole system is shimadzu). If it's air i flowcell, would cleaning with 2-propanol be a sugestion?

Regards
Ivar

[tom jupille]

Flushing the cell with IPA can't hurt.

Another possible cause for what you're seeing is "arc wander" from a lamp that's nearing the end of it's useful lifetime.