What is the cause of this baseline step

[Mike H.]

What would cause a step change in the baseline like this?

[chromatographer1]

An integrator timed event to the baseline or detector.

best wishes,

Rod

[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.

[danko]

It looks like wavelength change to me - in accordance to what Rod suggested above.
Please review your detector method/parameters.

Best Regards

[Vlad Orlovsky]

can be equilibration/saturation of ion-exchange/mixed-mode column with not fully transparent buffer/additive.

[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

[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?

[danko]

Hi Klaus,

How does pressure fluctuations influence the UV signal?

Best Regards

[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.

[carls]

Hi Klaus,

How does pressure fluctuations influence the UV signal?

Best Regards

Pressure instability means flow instability which does affect the UV signal

[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

[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

[danko]

You mean mixing problems. Could be. But nothing to do with the pressure itself.

Best Regards

[carls]

Pressure and flow are correlated. Pressure instability will give flow instability.

[danko]

Not so! But the other way around!

Best Regards