Filling The Sample Loop - Agilent Technologies 7697A Advanced Operation Manual

3
Method Development
Fill with constant volume
In this mode, the vial develops its natural internal pressure.
The HS sampler then inserts a fixed volume of gas into the
vial. In this case, the actual final vial pressure is not known,
since it depends on the initial pressure and the
compressibility of the added volume of gas.
Because the internal vial pressure is unknown, this mode
precludes using advanced sample loop fill options. The HS
will determine the best settings for filling the sample loop.
This mode is useful when the exact molar amounts are
important.
When using this mode, it is possible to develop insufficient
vial pressure. If the final vial pressure after sampling would
be < 1 psi (about 7 kPa), the HS will stop sampling when
the sample loop/vial pressure reaches 1 psi.

Filling the sample loop

The HS provides two modes for filling the sample loop:
Default and Custom. In the Custom mode, you can control the
amount of vial pressure used to fill the loop by setting the
final residual sample loop (vial) pressure and the ramp rate
for filling the sample loop.
Regardless of the mode, you should develop or add sufficient
vial pressure before filling the sample loop. Filling the loop
relies on the pressure differential between the vial and the
loop (which is vented to atmosphere). See Figure 12. With a
very low initial vial pressure, for example 7 kPa (1 psi), you
will rely more on diffusion than on gas flow for transferring
the sample to the loop. Results will suffer.
Advanced Operation 47