Where should the wool plug be positioned in my liner?

The simple answer is “wherever it works best”. However, I realize that is not a helpful answer if you either don’t have the time to experiment, or have tried several different packed liners without much success.

Please keep in mind that this is one of those questions which really does not have a right or wrong answer. I will provide you my opinion as to the best placement of the wool plug for reproducible results.

Let’s start with a single gooseneck liner, like shown below. Assuming the GC column is going to be installed into the left side of the liner (the gooseneck side), I would position the wool where the arrow points. The reason I would position the wool at this location is that many autosamplers are designed to inject into the middle of the liner, and you would want the wool plug to be below this position. Keeping the plug slightly above the gooseneck allows you to install the column into the gooseneck, which is where you will usually obtain the best reproducibility, without the risk of hitting/breaking the wool with the column. The position of the wool shown in the liner below is also an acceptable position to obtain good reproducibility, but I prefer the wool plug a little higher in the liner.  Please note this liner is designed for splitless injections (or split/splitless), but not split injections.

 

If you are looking for a split liner, an open-bottom liner is most commonly used, like the one shown below.  If the column is installed into the bottom of the liner, the wool, as shown, is in an appropriate position.

If you prefer "needle-wipe" injections, where the syringe needle is wiped clean through contact with the wool plug, be sure to choose a liner where the wool is held in place; this will prevent the wool from shifting positions in the liner.  An example of this type of liner is shown below.

 

 

Hopefully this post will help those of you who may be experiencing reproducibility issues with your current liner.  Through some experimentation, you should be able to find the exact position of the wool plug which works best with your liner and instrument.