Which GC injection port liner to use for gas samples

The answer seems fairly straightforward: Use a narrow internal diameter (ID) liner to keep peak shapes sharp by preventing band broadening; but this isn’t always the correct answer. There has to be enough internal volume in the liner to contain all of the sample.  Let me explain.

Let’s first look at liners when using purge & trap (P&T). All instrumentation that I am familiar with uses a transfer line from the P&T unit to the GC injection port.  In this case, you do want to use a narrow ID liner to minimize dead volume and prevent band broadening, especially for the compounds which will not condense and refocus within the capillary column.

Now let’s look at liners when using headspace (HS). Headspace units can transfer the sample to the injection port two ways:

(1) Using a Gas-Tight syringe to fill a sample loop (which is coupled to a transfer line).

(2) Using a Gas-Tight syringe and injecting directly into an injection port liner.

If the headspace unit uses a transfer line, then a small ID liner should be used. However, if a Gas-Tight syringe is used to inject the gas sample directly into an injection port liner, then a large ID liner is commonly used. 

 

(Splitless injections)

The liner below is a Restek Premium 4.0mm ID Single Taper Inlet Liner (23302), which is typically the best choice for gas injections of approximately > 250µL to 1mL.

 

The liner below is a Restek Premium 2.0mm ID Single Taper Inlet Liner (23315), which is typically the best choice for gas injections less than approximately 250µL.

 

(Split injections)

If you are injecting gases into a liner using a Gas-Tight syringe and splitting your sample, choose an open-bottom liner (with no gooseneck or other restriction at the bottom), like 23301 (photo below). Restek Premium 4.0 mm ID Straight Inlet Liner

 

If you are not using a syringe for sample introduction but instead the sample is from a purge & trap unit, headspace unit which uses a transfer line, or gas sampling valve, then the liner I usually recommend is 23333 (photo below).  Restek Premium 1.0mm ID Straight Inlet Liner

 

Please note that these are representative liners for an Agilent GC with a split/splitless injection port; the catalog number of the liner you would select depends upon your specific instrument and injection port.  In addition, make sure the injection port liner internal diameter (ID) is large enough for a transfer line to fit into the liner (if applicable).  For example, I have heard that some transfer lines have an outside diameter (OD) that is larger than 1mm OD; in this case, you would need to use a liner with a 2mm ID or larger opening, and not the 1mm ID liner shown above.  As an example, I recently found out that the Agilent 7697 Headspace Sampler requires a 2mmID liner like Restek 23313.

 

In summary, liner selection for gas samples will depend on your particular instrumentation and how the sample is introduced into the injection port liner. If your instrument uses a transfer line, then a small ID liner will likely provide you the best chromatography.  If a Gas-Tight syringe is used to inject the gas sample, a larger internal diameter liner will usually provide you the best results.