You’re ready to install a column into your GC and realize you do not have ferrules to do the job. But which ferrule do you choose? The parameters to consider when choosing the correct ferrule are instrument make and model, nut size and type, ferrule material, and column ID size. A visit to our ferrules home page will provide a general overview of variety of ferrules offered by Restek. By navigating the page, you can narrow the selection by choosing these parameters. This is the first in a series of posts that will hopefully make this selection process easier. We begin with Agilent systems because they have more choices available.
Capillary Column Ferrules
For this section, I will assume the GC is already configured to install capillary columns with 1/16 inch fittings. Restek offers two options on nuts and ferrules for Agilent capillary column installation. There are compact ferrules and standard ferrules, each with their own style of nut. The compact ferrule and nut are considered the Agilent-style. The broad taper on the compact ferrules was designed to match the taper on the bottom of the inlet seal. Standard ferrule and nut can also be used effectively on an Agilent system.
Here are the visual differences between the standard and compact ferrules:
Capillary Ferrules Compact Ferrules (Fit ≤ 0.28mm ID Fused Silica Columns)
Compact Ferrules (Fit 0.32mm ID Fused Silica Columns)
Compact Ferrules (Fit 0.45/0.53mm ID Fused Silica Columns)
Here are the catalog numbers of the corresponding applicable nuts:
This is a cross-cut look at the insides of the standard capillary nut and shows the length of the ferrule and the depth of the nut hole. This helps to show how necessary it is to match the ferrule with the proper nut; otherwise there will not be an adequate seal. If you are unsure which of these nuts you have on hand to install your columns, take note the Agilent style nut has a notch on the hex-nut portion, the standard does not.
“Compact” Agilent-style Ferrule and nut Standard ferrules and nut
Once you’ve matched the nut type to the correct ferrule type, now we need to match the capillary column ID to the ferrule ID. The table on sizes below gives an overview of how to match fused silica and MXT capillaries.
The next step in determining the correct ferrule is the material. The chart below explains the differences between the material choices. For installation into the inlet and most detectors, either graphite or the softer 60/40 vespel graphite should work fine. For GC/MS, it is recommended to use the standard, long ferrule vespel/graphite installed with an MSD source nut. This material is a good fit for MS because it will not fragment or allow oxygen to permeate into the system under vacuum applications.
Agilent has suggested that 100% vespel ferrules be only used for isothermal analysis.
MSD Source Nut
A note on the Agilent TCD, it has an 1/8 inch compression fitting port. In order to use our Agilent style or standard design nuts and ferrules you would need to have the Agilent supplied adaptor fitting. Restek does not have that fitting. Alternatively, Agilent does supply a two piece ferrule to install capillary column with a 1/8 inch compression nut. Restek does not sell the two piece ferrule and we do not recommend using a one piece graphite reducing ferrule.
Packed Column Ferrules
Typical Agilent packed column inlets are sized to accommodate ¼ inch OD packed columns; verify the fitting size of your inlet and detector. Agilent systems generally use standard compression style nuts and ferrules. If you doing on column injections, installing a 3/16 or 1/8 inch OD column will require inlet adaptors to center the column inside the ¼ inch injection port. If your instrument is equipped with an adaptor with a glass insert, on column injection will not be necessary, therefore a nut and ferrule would be all that is required to connect the column. Again you will need to verify the size nut and ferrule required. If you are installing a packed column into a capillary column inlet and detector we suggest a pig-tail configuration.
Notes on Agilent detectors- verify the size of the fitting required to connect the column. Agilent TCD’s for example are 1/8 inch compression fittings. If you want to install a 3/16 packed column, make sure your detector is adapted to accommodate ¼ inch packed column so you can use a reducing ferrule and ¼ inch nut.
Packed Column Inlet Adaptor
In summary, the key points to remember are:
- Match the ferrule with the proper nut
- Know the ID of your column to match with the correct ferrule size.
- Know system requirements for the ferrule material.
- For packed columns: Verify the fitting sizes of you inlets and detectors.
Look for future posts on nuts & ferrules for other instrument manufacturers. Thanks for reading.
I would like to thank my Colleague, Erin Herrold for her assistance and insight with this blog post.