Loop Fill Pressure; Loop Size; Valve Oven Temperature; Miscellaneous Settings - Teledyne Tekmar Versa User Manual

Loop Fill Pressure

A pressure setting is applied to the Loop Fill mode, which controls the pressure within the loop prior to transfer to
the GC. The higher pressures in the loop result in more mass in the loop. This directly affects sensitivity as well as
eliminates variation in atmospheric pressure. Typically, a Loop Fill pressure is selected that is 2-3psig below the vial
pressurization setting for a 1mL loop (Standard). When using smaller loops, this pressure delta can be reduced and
when using larger loops, the delta may need to be increased to allow for the loop to be correctly filled.

Loop size

Volume is controlled by the size of the loop selected. The standard loop that is shipped with the unit is 1mL. Teledyne
Tekmar offers loops from 0.1mL to 5mL. The larger the loop, the more sample gas is transferred on column. It should
be noted that before deciding to use a larger loop, due to the increased sensitivity, all other optimizations should be
exhausted. The reason this is recommended is because the larger loops require more time to be flushed on column,
thus potentially causing reduced performance by the GC.

Valve oven temperature

The temperature of the loop also indirectly affects the mass transferred to the column. Lower valve oven temperatures
result in a gas with a higher density in the sample loop prior to transfer. The higher density increases the amount of
analytes on column thus increasing the sensitivity. Valve oven temperatures need to be selected with both sensitivity
and carryover in mind. Low valve oven temperatures may result in higher sensitivity, but also higher carryover. The
recommended starting points for the valve oven temperature are 0°- 5° above the Sample Equilibration Temperature.

misCeLLaneoUs settings

gC Cycle time

The Versa uses a GC cycle time to calculate when to start the next vial. The GC cycle time allows for the highest
through-put of samples as well as insures that all samples see the same thermal exposure time. The GC cycle time,
which is entered by the user, is "From Ready to Ready". This means from the time when a run is started until the GC
becomes ready again (the analysis, plus the cool down and equilibration time). When determining this time, it is
recommended you estimate high to take into account any room temperature changes that may occur that will affect
the GC cool down time.
NOTE: If the GC is not ready in the time the user inputs, the Versa will wait with the sample pressurized until the GC
becomes ready, potentially resulting in vials being exposed to too much thermal exposure time.
Method Development • Page 6-6
Versa User Manual www.teledynetekmar.com