Pressurizing The Vial - Agilent Technologies 7697A Advanced Operation Manual

3
Method Development

Pressurizing the vial

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directly to the GC column.
As described in Valve and loop
the vial, then vents the vial to atmosphere through the
sampling loop. The HS can control the rate of gas transfer
through the loop, as well as the initial head pressure within
the vial and the residual pressure left in the vial when
sampling ends.
• For more repeatable results, make sure the vial contains
sufficient pressure to sweep the sample loop more than
once. If the vial develops less than 70 kPa (10 psi)
pressure during thermal equilibration, consider adding
additional gas to increase that pressure. If the vial
pressure is low, it can cause repeatability issues or low
peak areas (due to insufficient sample reaching the
sample loop).
• The HS can pressurize the vial using 3 different modes.
Use a vial pressurization mode appropriate for the
sample.
• Set a target vial pressure higher than the pressure
developed during thermal equilibration. (Otherwise, you
will accidentally vent sample!)
Fill at flow to pressure
This is the default vial pressurization mode, and is suitable
for most analyses. The HS uses a fixed flow rate to
pressurize the vial to a specified level. This provides less
"shock" to the vial.
• Avoid a high flow rate if the change in vial pressure is
small.
• Custom sample loop fill options are available when using
this mode.
Fill to pressure
In this mode, the HS pressurizes the vial to the target level
as rapidly as possible. This mode duplicates the process
used on earlier Agilent headspace samplers (G1888 and
7694). Custom sample loop fill options are available when
using this mode.
systems, the HS pressurizes
Advanced Operation