Does the Amount of Wool in Prepacked Liners Matter?-Part I: Experimental Setup

If you’ve followed my previous blogs on GC liner selection, you will know that the wool in inlet liners plays an important role for both split and splitless injections (GC Inlet Liner Selection, Part I: Splitless Liner Selection and GC Inlet Liner Selection, Part II: Split Liners).  Just to review, wool can enhance vaporization, promote sample mixing, and protect the column from non-volatile matrix material.  At Restek, many liners we sell come prepacked with wool; in the case of Topaz liners, this wool is deactivated in place, giving superior inertness, as it eliminates the need to handle the wool post-deactivation, potentially breaking fibers and exposing active sites. Customers that pack their own liners will likely notice performance differences based on the amount of wool, since the fibers break and expose active sites.

We have received questions about the amount of wool that comes packed in these liners, with customers noticing one liner appearing to have slightly more wool than another.  One question that comes up is “how does the amount of wool affect performance?”.  “Does too much wool cause bad performance?” To address these concerns, I set up an experiment to observe the effect of wool density on liner performance.

First, I should point out that Restek’s liners have specifications for wool, including both the length of the wool plug, as well as a target weight.  I looked at liners within this specification, ranging from the shortest, heaviest wool plug (most dense) to the longest, lightest wool plug (least dense).  In addition, I examined a few liners that were packed well beyond the specification (double and triple the typical weight) to see what performance differences these extremes introduced.

For these experiments, I requested liners to be packed to the specifications shown in Table 1.  The first four liner groups represent upper and lower specifications for wool plug length and weight.  The last two liner groups are packed at double and triple the typical upper weight specification, respectively.  All liners were Topaz and were deactivated with the wool in place.

Table 1: Liners to be tested, covering the upper and lower range of specifications for wool plug length and weight, as well as liners that are packed at 2 to 3 times the specified weight of wool.

I tested 2mm single taper liners with wool.  I chose the 2mm ID because the narrower ID would exacerbate any flow issues with wool due to the increased restriction.  I used the single taper format because I wanted to test in splitless mode, as I felt that the slower flows for splitless injections would exhibit the largest effects from differences in wool packing, if any.

The next thing was defining performance criteria.  What types of performance could wool density or amount specifically impact?  One of the obvious choices was inertness, as there is always a concern that wool is difficult to thoroughly deactivate and can introduce activity; therefore, more wool or denser wool potentially equals more activity. I also examined retention, especially of more volatile compounds.  The idea was that a higher density of wool could lead to more back pressure, causing the instrument to calculate flows differently, leading to differences in retention time.  There is also the possibility of increased retention through analytes interacting with the wool.  In addition, I monitored tailing factors, as tailing could possibly be attributed to active sites or increased retention from the wool.

After obtaining the custom packed liners, I tested each liner with an acids and bases mix for activity, as well as a volatiles mix to look at any differences in retention/flow.  The following GC method was used to test liners:

Stay tuned for Part II to see what I found out!

Part II:

Does the Amount of Wool in Prepacked Liners Matter?-Part II: Results

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