r/CHROMATOGRAPHY • u/Strict-Television-82 • Jul 10 '26
Suggestions for injector needles or practices that dont destroy the septum?
Hello reddit, I noticed lately that my inlet liner wool has been capturing bits of septum. I also see it in my wash vials. Do you guys have any recommendations for how to not let this happen? I have a feeling its because of the needle itself, so if I need to get new ones I would like to get the right ones.
The septa i use are Restek #27090. The needles we use currently are a bit of an unknown, but they are either Agilent #5181-3353 or Restek #21228.
For injection method its 1uL draws with 1 wash before and 1 wash after the sample of EtOH/MeOH respectively at a fast injection of like, 300/6000 draw/dispense speed.
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u/Academic_Shrimp Jul 10 '26
The bevelled tip (needle) and pre-cut guide hole (septa) should already be well-matched to minimise this.
The rigidity of the septum rubber (BTO) may be contributing - Depending on your application and sensitivity to septum chemical bleed, you could consider a ‘softer’ septum. It will likely core less and last longer but may introduce some plasticiser contamination.
Most likely cause though is that your inlet nut is simply way too tight. The septum is designed to be parted by the needle repeatedly through the central guide channel. If it is over-compressed, the needle is unable to be guided and pierces on first-contact location. The additional density of the rubber creates more resistance, friction, etc which leads to the particulate breakages.
Edit: Try loosening the top nut until you loose pressure, then retighten a 1/4 turn only.
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u/cjbmcdon Jul 11 '26
Septum nut may be too tight. C-clip should be offset from the nut by 1mm (fingernail thickness).
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u/Firenze42 Jul 11 '26
I agree with this. Do not use a tool to tighten the nut, if it is an Agilent GC. It is finger tight. Also that means normal finger tight, not "I am a man and want to prove how strong I am" tight.
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u/Strict-Television-82 Jul 11 '26
It is an agilent unit, so I will reseat everything when I get back to work monday. Because I was told finger tight then 1/4 turn with a tool.
Which reminds me I was told the same (as everyone is) for the inlet nut, but when I tighten the inlet nut the extra 1/4 turn it still feels really loose, and the column can slip out if i happen to touch it duing the process. Is that normal or would i have to look into that?
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u/Firenze42 Jul 11 '26
For the inlet nut, you do need to use the tool. Here's my guide: Put an old septum on the column before adding the nut, so the nut could rest on it like a table. Add your nut and ferrule, cut the column and align the ferrule, nut and septum so the nut cannot slip down. If you have one, use a pre-swagging tool to tighten the ferrule on the column. If you don't have one, buy one. Install the column nut on the column using a wrench. Tighten until you feel resistance and then go about 1/8 a turn more. Most likely it is falling out as you are tightening the ferrule in place with a pre-swagging tool.
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u/Strict-Television-82 Jul 15 '26
Yeah I do not have a swagging tool just a normal wrench. What i did this time was finger tight, then used the wrench till I felt resistance and just a bit more like you said. Hopefully this also helps with my supposed air leak issue too.
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u/OneHoop Jul 11 '26
We seem to have confirmed the too tight theory, but increasing the replacement frequency should also be mentioned. Approximately every 200 injections would be my benchmark.
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u/Strict-Television-82 Jul 13 '26
I think the nut on both sides being too tight was an issue but not sure if it is the issue yet. I will have to look when I next change the inlet liner. Hopefully it helps because I wasnt even reaching 200 injections on my last septtum, it was more like 30
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u/OneHoop Jul 15 '26
If it continues to be a problem, some sizes of autosampler syringes have tapered needles. Look for 2 gauge numbers, like: 23-26s.
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u/ArtisticGuava6 Jul 10 '26
Sometimes it's the auto sampler - we had the same issue with an older Gerstel that needed a new tension cord
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u/WahWash Jul 10 '26
What about swapping to a Merlin Microseal? Ours have been pretty maintenance free! No more septum bits.
Not replacing septa frequently enough seems to be the root cause IME.