Waters ACQUITY UPC2 - Page 37

November 16, 2016, 715004521 Rev. C
Page 37
3.2.4.1 Setting up a pressure gradient
Some classes of compounds require the use of 100% liquid CO
2
to elute off the column. When
using 100% liquid CO
2
, you can set up a pressure gradient to increase the solvent strength
(density) of the liquid CO
2
, which is similar to setting up a solvent gradient to increase solvent
strength.
Figure 3–1: Pressure gradient example
When setting pressure gradients, observe these guidelines:
• Higher ABPR pressures increase density and decrease retention times.
• Lower ABPR pressures decrease density and increase retention times.
ABPR pressure
ABPR
pressure
Retention
time
Longer
retention
time
Shorter
retention
time
CO
2
No pressure range left
to allow for a pressure
drop across the
column