Mmi Split Mode Minimum Operating Pressures - Agilent Technologies 7890 Series Advanced Operation Manual

3
Inlets
If using cryo as the coolant when configuring the initial inlet
setpoint, set the Use cryo temperature equal to or higher than
the inlet setpoint to cool the inlet and hold the setpoint
until the inlet temperature program exceeds the Use cryo
temperature. If the Use cryo temperature is less than the inlet
setpoint, cryogen will cool the inlet to the initial setpoint
and turn off.
If using compressed air as the coolant when configuring the
initial inlet setpoint, Use cryo temperature behaves differently
when in Compressed air mode than it does when in N2 cryo or
CO2 cryo mode. In Compressed air mode, the air coolant is used
to cool the inlet regardless of the Use cryo temperature setpoint
during the cooling cycle. If the inlet reaches setpoint, the air
coolant is turned off and stays off. If the oven temperature
is high enough or the inlet was very hot previously, it is
possible that the inlet temperature will rise and the GC will
go not ready. For this reason, it is better to set the
instrument cooling configuration as N2 cryo or CO2 cryo when
using compressed air as the coolant. When using compressed
air, the LN hardware cools the inlet faster than the LCO
2 2
hardware. Never use LCO or LN when the instrument is
2 2
configured in Compressed air mode.
If cryo is turned on, and if the inlet is cooled during a run,
cryogen is used to achieve the setpoint. This may have a
negative impact on the chromatographic performance of the
oven and cause distorted peaks.
When a method ends, the cooling setpoint returns to the
initial state of the method, unless you load another method.
To conserve coolant when the GC is idle, load a method that
does not use a cooling configuration.

MMI split mode minimum operating pressures

The minimum recommended inlet total flow is
20 mL/minute. When the inlet is operated in a Split mode,
there will be a minimum pressure at which the inlet can
operate. Typically, low inlet pressures may be required for
shorter, wide bore columns. The minimum pressure is a
function of carrier gas type, total inlet flow, liner design,
and possible contamination of the split vent tube or trap.
A wide bore column requires a much lower inlet pressure
than a typical capillary column to maintain a given flow.
Setting the split ratio (total flow) too high when using a
wide bore column can create an unstable control
relationship between the pressure and flow control loops.
Advanced Operation Manual 57