Graphite/Polyimide
(15% is common) greatly reduces binding .
The mixture retains the benefits of:
Being able to be molded into desired shapes
High temperature stability
Ferrule does not extrude when tightening
Can seal against imperfect surfaces
Has low air permeability
Soft enough for use with fused silica
Because of these benefits, graphite/polyimide ferrules are the dominant ferrule type when making
fused silica column connections in the GC oven.
Graphite/polyimide ferrules do tend to shrink with temperature cycling, so they need to be retightened
several times (after cool down) within the first 10 temperature programmed runs or so.
Extended use above 300degC also tend to "dry out" the polymer and may carck on re-tightening
PTFE ferrules
and other similar fluoro polymers ( PFA and ETFE ) are very inert
and have minimal interaction with samples and solvents.
They are very easy to seal, often requiring only hand tightening.
When disconnecting fittings, PTFE fittings slide right off the tubing and can be re-used multiple times.
However, PTFE ( TEFLON ) they have the most restricted upper temperature limit (250degC)
and are somewhat permeable to air, so use inside the GC oven is quite limited.
PTFE ferrules are used primarily for low temperature applications requiring the
most inert connections, and for tubing connections outside the oven - for more reliable, easily
adjustable and removable connections.
PTFE ferrules are lower cost and are often used for compressed air supply lines for valve actuators.
ETFE
(Tefzel) is a melt polymer compare to PTFE (which is sintered) and thus harder
and less air permeable than PTFE and often preferred for solvent lines in LC/HPLC applications
PBI Ferrules
( experimental by Chromalytic ) . . . offer potential higher temperature useage
than Polyimide versions fused silica and GC/MS are targeted uses
Customer feedback on PBI Ferrules s welcome
Website :
E-mail :
TelNo : 03 9762 2034 . . . in AUSTRALIA
