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What is the cause of this baseline step
Posted: Thu Sep 01, 2011 5:50 pm
by Mike H.
What would cause a step change in the baseline like this?
Re: What is the cause of this baseline step
Posted: Fri Sep 02, 2011 1:25 am
by chromatographer1
An integrator timed event to the baseline or detector.
best wishes,
Rod
Re: What is the cause of this baseline step
Posted: Fri Sep 02, 2011 12:16 pm
by Bintang
I had similar problems at the University using UV laps well past theír actual life time , went away when we finally invested in a new lamp.
If it is reproducible then I would agree with previous poster.
It is absolutley electronic in origin.
Re: What is the cause of this baseline step
Posted: Tue Sep 06, 2011 3:07 pm
by danko
It looks like wavelength change to me - in accordance to what Rod suggested above.
Please review your detector method/parameters.
Best Regards
Re: What is the cause of this baseline step
Posted: Tue Sep 06, 2011 3:57 pm
by Vlad Orlovsky
can be equilibration/saturation of ion-exchange/mixed-mode column with not fully transparent buffer/additive.
Re: What is the cause of this baseline step
Posted: Wed Sep 07, 2011 10:24 am
by unmgvar
if you make a step gradient then you can see such behavior in the baseline
if you change the wavelength in mid run and do not do an auto-zero as well then you can get this behavior as well
Re: What is the cause of this baseline step
Posted: Fri Sep 09, 2011 2:28 pm
by Klaus I.
What would cause a step change in the baseline like this?
If this happen frequently at different time points, I am also think the lamp is bad.
The baseline between 3 and 7 minutes is also interesting, is this corresponding to a pressure fluctuation or is this a mixing problem?
Re: What is the cause of this baseline step
Posted: Fri Sep 09, 2011 2:58 pm
by danko
Hi Klaus,
How does pressure fluctuations influence the UV signal?
Best Regards
Re: What is the cause of this baseline step
Posted: Fri Sep 09, 2011 8:22 pm
by nschwartz
Obviously the change occurs at a specific time, so I would look at the timed program. What is it that you have changing at the distinct time? Looks most likely to be a change in attenuation or something of that nature.
Re: What is the cause of this baseline step
Posted: Sat Sep 10, 2011 2:36 pm
by carls
Hi Klaus,
How does pressure fluctuations influence the UV signal?
Best Regards
Pressure instability means flow instability which does affect the UV signal
Re: What is the cause of this baseline step
Posted: Sat Sep 10, 2011 3:19 pm
by danko
Pressure fluctuation e.g. rise does not equal flow rate increase for instance. It could happen - and it happens all the time - that the gradient mixture changes towards more viscous nature. An example could be from watery to IPA containing eluent.
Best Regards
Re: What is the cause of this baseline step
Posted: Sat Sep 10, 2011 3:38 pm
by carls
The noise early in the chromatogram is typical of a pump problem commonly seen with binary pumps when one pump (A or B) is not functioning properly
Re: What is the cause of this baseline step
Posted: Sat Sep 10, 2011 3:51 pm
by danko
You mean mixing problems. Could be. But nothing to do with the pressure itself.
Best Regards
Re: What is the cause of this baseline step
Posted: Sun Sep 11, 2011 9:57 pm
by carls
Pressure and flow are correlated. Pressure instability will give flow instability.
Re: What is the cause of this baseline step
Posted: Mon Sep 12, 2011 7:32 am
by danko
Not so! But the other way around!
Best Regards