Change the GC inlet liner – When?

I mentioned in my last post on GC inlet liner performance degradation that the liner should be changed to restore performance after dirty sample injections, but as several ChromaBLOGraphy readers already pointed out, I didn’t show the data to support that claim.  Consider it done here…

In review for the previous post, after splitless injections of used motor oil, later eluting PAH response degraded over a relatively short time, eventually showing less than 25% of the original response in some cases (chromatogram below), even with a proper splitless purge valve time that allows good sample transfer.  Changing to a Restek Premium 4mm single taper with wool liner immediately brought back the PAH responses to where they were when the experiment started.  Interestingly, I did not have to change the GC inlet seal or trim the column for maintenance, which highlights the effectiveness of the liner wool packing for protecting other sensitive (and more expensive) parts of the GC system.

So when should you change your GC inlet liner?  Two suggestions:

When performance degrades.

• Use a standard containing your compounds of interest, or an abbreviated version with compounds sensitive to inlet liner performance degradation, and when a peak’s response degrades from the original response outside a range important to you (10, 20, 30%?), change the liner.
• Depending on how dirty the samples are, analyze this standard often in the sample queue, maybe even after every 5^th or 10^th sample, to gauge inlet liner performance.

On a preventative maintenance schedule (my recommendation).

• Every day, every week, every month, every sample queue, depending on sample type and cleanliness.
• Don’t let trouble develop that causes lost analysis time.  Change the liner before performance degrades.
• The liner is the cheapest part of the immediate GC flow path (liner, seal, column), costing about 1/20 of most GC columns.

Although I didn’t do it in this experiment because I wanted to prove the point about liner/wool dirtiness causing problems, when I perform maintenance on my GC inlet, I “shotgun” it.  That is, while I have the inlet open and cool, I change the septum, the liner, the liner o-ring, and the inlet bottom seal.  This is my “preventative maintenance” way of not allowing problems to develop.

Here are the inlet supplies I always keep handy for an Agilent split/splitless inlet when I’m doing splitless injection:

• Thermolite 11mm septa (perfect for Agilent GC inlets at most temperatures used; softer and so don’t core like harder BTO septa can)
• Viton O-rings for Agilent GC liners (easy to seal, good temperature range)
• Restek Premium 4mm single taper with wool liner for Agilent GCs (best Restek liner deactivation)
• Dual Vespel Ring Inlet Seals for Agilent GCs (I prefer the gold-plated ones for their inertness)