Chromatography in particular has VERY demanding requirements
- obtaining efficient sealing of columns and other parts into instrument
systems
Typically, ferrules ideally, need to be . .. - malleable/"squashable" without risk to breaking glass/fused silica columns or fragile tubes.
- for GC : capable of withstanding high temperatures ( for GC >300-deg C ) with recycling.
- for HPLC - high pressures ( >5000psi ) and compatability with solvents
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HPLC - high pressures 6-8000psig, compatability with solvents and buffers PEEK is ideal - "squashable & resusable inert to "most" solvents -low temperature usabilty of approx 200degC Teflon for example is too soft for HPLC although quite adequate for low pressure chromatograpy;
FIA etc
Most instruments use stainless steel ferrules and they are the "state of the art" but there can be a distortion / re-sealability problem with continued use if overtightened or columns are changed often |
GC - ALL seals MUST be gas-tight; capable of withstanding high temperatures
- typical GCs work at pressures up to 60psi and column temperatures even up to 430-deg C
with the new high temperature phase columns now becoming available. MORE IMPORTANTLY - they should maintain their seal integrity even during routine temperature cycling
under temperature programmed column conditions GRAPHITE is ideal for most GC applications
and a standard low-cost, one-piece design is quite adequate For more demanding applications such as GC/MS where air diffusion may be a problem
THEN Graphite/Vespel is preferred by many chromatographers.
"Vespel" ferrules are generally limited to about 300C due to a phase transition at about 280C where the Vespel tends to soften with loss of seal; temperature cycling can also be an issue until the Vespel actually "cures"
although then they can have a tendency to crack Encapsulated graphite ferrules solve most of these problems !
-
Chromalytic has developed several designs for both encapsulated "straight"
and reducing Graphite Ferrules
ENQUIRE
this minimises fragmentation and flaking of the graphite |
GC FERRULE Material ??? -
Teflon; PEEK is RS - limited to 270-deg C max and
- Stainless Steel is not suitable with "glass" columns of course
- VESPEL ( and its derivatives ) can be used to about 320-deg C;
100% Vespel is too hard and difficult to use withou risk of cracking the glass column
40% Graphite/Vespel
is also OK to 320C and is much softer UNFORTUNEATELY is very expensive being availbale ONLY from Dupont - tends to distort more readily under high temperatures
15% Graphite/Polyimide ( an alternative lower cost material ) is used by Chromalytic and is a reasonable compromise in hardness, resuability and cost
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Ferrule
"PROBLEMS"
"VESPEL"
Use with care when temperature cycling - like most polymers which generally have phase transitions, they tend to "flow" - retighteing may be required until the material has "cured"
At prolonged high temperature they tend to "dry-out"; retightening may cause them to "crack" with loss of sealing.
Machining tolerances are critical - the Vespel is so hard it hardly deforms at all in the cold-state.
The ferrule ID must be closely matched to the column
OD to within +0.003-in or 0.075mm
- NOT a pretty job for the average laboratory "hacker", but for US no problem !
- we're pretty handy with a lathe
GRAPHITE
They are more porous than VESPEL and in conventional fittings reducing ferrules are difficult to seal effectively in GC/MS use, particularly at the column outlet under vacuum. Whilst perfectly satisfactory for most GC use above ambient pressure THEY DO tend to
diffuse air under vacuum
In conventional fittings eg 1/16-in OD; IF the graphite is overtighten particles of graphite may be sheared off/extruded into the fitting hole and subsequently may even cause problems in blocking FID jets, GC/MS jet seperators etc Use VESPEL ferrules for these applications
OR
Use the NEW Chromalytic
"encapsulated" Graphite Capture Ferrule Adaptor Fitting Cat.# GCFA
similar to seal used in Fison/CE 8000 GC/MS |
GENERAL USE
- Instrument Prototyping etc
EVEN with metal tubing . . .
Metal Ferrules CAN be a real "PAIN in the Neck !"
they distort - repeated re-connection can be troublesome particularly for larger tube diameters
You want to make changes - THEN YOU MAY HAVE TO CUT OFF THE FERRULE
WITH GRAPHITE FERRULES . . .
Just slide the nut and ferrule off AND Re-USE
Certainly for most tube applications graphite IS the ideal ferrule material. |
APPLICATIONS
Capillary GC
Graphite ferrules have been an integral part of the capillary GC revolution - they are so soft and flexible that they will deform to make an ideal seal for most applications
They're ideal for . . . - packed glass chromatography columns ( typically 1/4-in OD ) AND larger
- diameter ceramic catalyst tubes
- Ideal for PREP scale GC columns AND even with SS columns there's a cost saving
THEY are re-usable AND slide-off the tube
YOU don't have to cut them off
SS ferrules on SS tube
- THEY can be a problem due to distortion of the tube and getting them to re-seal after being overtighef "the bigger the tube the bigger the problem"
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PRICING ( see our Price List for current prices on ALL products ( CATALOG Search )
GRAPHITE DESCRIPTION : up to 1/4"ID
Graphite Ferrules Aud$25.00 /10pk for All sizes
Thats OUR retail price ONLY USD18.00 AND PER 10
Attractive Discounts . . . for OEM and Bulk Orders
Custom Sizes : ANY Quantity - NO Problem
( although a Tooling Cost MAY apply for small quantities if it's an unusual size 0
Graphite ALL SIZES from 0.3mmID and up to
1.0" ( 25.4mm ) ID - Straight / Reducing and Metric Sizes to suit ALL commonly avaiable Swagelog / Parker etc tube fittings
GRAPHITE / VESPEL(polyimide)
Price is limited by the current exhorbitant price of raw material
BUT . . .
If YOU can get the material at a reasonable price
THEN We can machine it for you
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