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Wool vs fritted liners – which is better for controlling dirty matrix?

28 Sep 2023

Choosing the right liner for your application can critical to achieving the separations you need, and getting the most cost-effective analysis possible. Anyone working with a matrix containing non-volatile compounds (NVCs) knows all too well how important using wool-plugged or sintered glass frits are. The extra surface area provided by glass wool and frits allows for even volatilization, and capture of those NVCs. 

When it comes to the analysis of semi-volatiles in harsh environmental matrices, you are more likely to encounter NVC’s that wreak havoc on injection repeatability and lifetime. So how do you decide whether to use the frit or the wool liner?

We compared Restek’s topaz splitless liner with wool (Cat.# 23303) to a fritted liner competitor using a semi-volatiles specific quality test that gauged repeatability of injections with regular column trimming maintenance.

Methods:

Peak area ratios of semi-volatile analytes were normalized to non-reactive alkanes:

  • H/T = area 1,6-hexanediol / n-tridecane (OH group interactions)
  • D/A = area 2,4-dinitrophenol / acenaphthalene-d10 (nitrogen interactions)
  • E/T = area 2-ethylhexanoic acid / n-tridecane  (acidic interactions)
  • P/A = area pentachlorophenol / acenaphthalene-d10 (chlorinated interactions)

The quality mix was injected three times, followed by ten injections of used motor oil matrix, then the quality mix was injected three more times (“fouling”). This was repeated five times, and the 50cm of column was trimmed between each round (“trimming”). This was repeated with three of each liner.

We measured peak area ratios of the third quality mix injection, and compared performance between the topaz and fritted liner with regular column maintenance. The change in peak area ratio between each fouling and trimming cycle was measured and plotted to determine which liner performed better with regular column trimming.

Results and conclusions:

Changes in peak area ratios with repeated “fouling” and “trimming”

Figure 1. Changes in peak area ratios with repeated “fouling” and “trimming”.

While there wasn’t a very consistent trend of peak area loss or gain during analysis with either liner, there was a marked difference in area consistency and repeatability, especially with 1,6-hexanediol. Restek’s topaz liner showed more consistent peak area ratios than the fritted liner competitor over repeated “fouling” cycles. This suggests that more inlet maintenance is necessary to achieve consistent results with a fritted liner if you are working with a dirty matrix. One explanation could be difficulty deactivating within the frit, leaving active sites that affect chromatographic repeatability.

So which maintenance is ‘better’? Labs, rightfully, want to avoid frequent maintenance. Opening up your instrument means introducing more potential sources of error such as contamination and leaks. When changing the liner, you break at least three points of contact: liner/o-ring, liner/septa, and liner/seal. This means that every time you change the liner, there are three potential sources of issues. However, when you trim the column, you really just have one contact being broken: column/seal. One could therefore argue that trimming the column is a “safer” approach to controlling contamination than changing the liner; but only if it makes the right improvement.

Figure 1 shows that column-trimming was able to sufficiently restore/maintain chromatographic results when using the topaz liner, but not so much with the fritted liner. The fritted liner’s more erratic results imply contamination collected somewhere in the inlet, and could not be controlled with column trimming. So, that means opening up those three contact points for maintenance. But don’t worry, leak checking your inlet is a breeze with a Restek leak detector (Cat.# 28500), regardless of your reasons for maintenance.

There is also the advantage of cost with a wool-plugged liner. A liner with wool is always going to be less expensive than a fritted liner, so when do the benefits of the frit really outweigh the drawbacks? This answer is always going to depend on your specific analysis. The test in this blog measured the performance of just four analytes and two alkanes, representing a range of compound classes and potential analyte-liner interactions. While there is plenty of valuable insight to be obtained, there are plenty of reasons a fritted liner might work better for your work. The fritted option exists for a reason! Frits themselves are a more repeatable structure, and the pores are wider and encourage better mixing and flow of analytes for potentially less time in the liner. Anyone analyzing endrin or DDT knows how important the time spent in the liner is – and keen observers will notice those two compounds were not included in this study. Frit pores are still vulnerable to buildup of NVCs though, just like wool-plugs, and if your matrix is dirty enough to plug frit pores, your inlet maintenance just became a lot more expensive.

Have questions about what liner is best for you? Reach out to our customer service team, or peruse more literature on ChromaBLOGraphy.