Strange pressure profile on Aquity

[bunnahabhain]

Dears

I have a simple gradient (A= ACN, B=water):

Code: Select all

time    %A  %B
0       40    60
10      70    30
10.01   40    60
14      40    60

But a relatively strange pressure profile for it:


Any idea what could cause this step?

Thanks
Jörg

[tkubowicz]

Hello

When you change gradient rapidly (10.0 to10.01min) it will take some time for "old" mobile phase to pass through the LC plumbing (capillaries + column). So I think that's what you see between 11-13 min.
You can replace column with restriction capillary to see if the profile is the same.
Also you will see different profiles for Bin/Quat pumps.

Regards

Tomasz Kubowicz

[HPLC chemist]

I agree with Tomasz. Going from 70% to 40% ACN (a low viscosity and low pressure solvent) in several seconds will radically change your pressure profile. You can slow down this gradient ramp which should equalize the pressure profile (if it interferes with your separation).

[bunnahabhain]

OK, I understand pressure is going back to the starting conditions but I would have expected a continuous rise instead of a 1.5 minute step with somewhat constant pressure during re-equilibration.
But it does not interfere with the separation - so what
Regards
Jörg