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

In Part I of this series titled "Does the Amount of Wool in Prepacked Liners Matter?-Part I: Experimental Setup", I posed the question of the impact of the amount of wool on liner performance.  As a reminder, this study specifically examines Topaz liners that are prepacked with wool and then deactivated. With your own hand-packed liners these results will not apply.

The first criteria I wanted to examine was inertness, as it’s generally the largest concern when using wool.  Since wool has a high surface area, it can be difficult to thoroughly deactivate, leading to the theory that the more wool, the more activity.  While this is likely true if you’re packing your own liners, the results for the Topaz liners in this study, where the wool was deactivated in place, did not show this trend.

Average response factors for active acids and bases injected splitless at 0.5 ng on different liners can be found in Figure 1:

Figure 1: Average relative response factors for several active acids and bases for each group of liners, organized by weight-length of wool plug. Non-reactive compounds are included for comparison. Error bars represent 1 standard deviation.

As you can see from the above results, differences in relative responses for most of these active compounds were small, even with liners that were overpacked (10 mg and 15 mg of wool).  On the other hand, for 2,4-dinitrophenol, an often-troublesome acidic compound, the liners that were packed with 15 mg of wool showed a significant decrease in response.  Interestingly, for two of the difficult to analyze bases, dicyclohexylamine and benzidine, response factors slightly increased as wool amount increased.  Perhaps the wool has a slightly basic character.

The above data is presented using a response factor, n-tridecane as an internal standard.  This allows us to examine differences caused by activity by normalizing to the internal standard.  But what if we remove this normalized data and see the general effect on vaporization? Figure 2, below, illustrates raw peak area for the acids and bases for the different liner groups.

Figure 2: Average peak area counts for several active acids and bases for each group of liners, organized by weight-length of wool plug. Non-reactive compounds are included for comparison. Error bars represent 1 standard deviation.

Notice that the overall trend is that peak areas tend to increase as wool amount increases, though the differences are generally pretty small.  This could be due to the enhanced vaporization from the higher surface area of the wool.  2,4-dinitrophenol is an exception, as you can see the large loss in area when overpacked with 15 mg of wool.

Besides response factors and raw area response, we can also examine tailing factors of active compounds.  Figure 3 shows a comparison of tailing factors for select active compounds.  There were not any significant differences, even with the liners that are very overpacked with wool.  I found this interesting for 2,4-DNP, since I did observe a reduction in response on the 15 mg packed liners, yet the tailing did not increase.  This tells me that 2,4-DNP is likely experiencing irreversible adsorption within the wool, rather than reversible, which might be exhibited by increased tailing.

Figure 3: Tailing factors for select active compounds for each group of liners, organized by weight-length of wool plug.

In addition to inertness, I wanted to examine retention times of volatile compounds, which could be affected by flow differences or increased interactions with the wool.

The most volatile compound in this study was cis-1,2-dichloroethene.  As everything else in the system was left unchanged, any differences in retention should be due to the differences in wool packing.  The average observed retention times for each group of liners is shown in Figure 4 below.

Figure 4: Retention times of cis-1,2-dichloroethene for each group of liners, organized by weight-length of wool plug.

The liners with more wool had more retention of cis-1,2-dichloroethene.  For the liners packed with 15 mg of wool, this volatile compound eluted around 4 seconds later than the liners that were packed within specifications.  While differences are seen when packed far beyond the specifications, liners at the upper and lower specs for wool did not show significant variation in retention time.

If we look at the most volatile compound from the active acids and bases mix, 4-picoline, we can see a similar trend (Figure 5).  The liners with 15 mg of wool showed a 6 second increase in retention for 4-picoline.

Figure 5: Retention times of 4-picoline for each group of liners, organized by weight-length of wool plug.

One final observation was with regards to liner “bleed”.  Generally, upon installing a new liner, you may notice some peaks that are related to excess deactivant “bleeding” off of the liner, especially during the first injection or two.  In general, I have observed very little bleed coming off of Topaz liners.  I did observe, however, that the liners that were packed at 2 or 3 times the weight specification for wool showed increased bleed on an initial solvent blank (Figure 6).

Figure 6: Liner bleed comparison between 3 mg, 10 mg, and 15 mg wool plug on first injection after installation. The boxes highlight differences, with the 3 mg liners showing no significant bleed peaks.

Conclusions

The above data demonstrates that for Topaz liners packed within the specifications, there are no major differences in performance based on the amount or density of the wool.  When packing at 2-3 times the maximum weight specification, there were some differences observed: 2,4-DNP response was negatively affected, retention time shifts occurred, and there was increased liner bleed.  I believe the lack of differences observed in many cases is owed to the deactivation process itself, with the wool being deactivated in place using vapor deposition.

I don’t want to sound like a broken record, but I’ll again point out that results may look completely different if you are packing your own liners.  This is due to breaking fibers and exposing active sites during the process.  If anything, this data should help to further convince you to try prepacked liners with the wool deactivated in place, since in addition to superior inertness, you will get better reproducibility.

To see more information about the experimental set-up, visit Part I:

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