Quick question. I’m seeing carryover and fragile tip failures using 65 µm PDMS/DVB during headspace GC-MS of low-level amines from fabric singe residues and, separately, postmortem blood (15 min at 60°C). Anyone settled on a more robust coating (CAR/PDMS or DVB/CAR/PDMS) and a conditioning routine that tames background siloxanes without losing the trace hits we care about?
For the 15 min at 60°C HS, I’ve had better luck with 85 µm CAR/PDMS StableFlex plus a basic pre-condition: 25–30 min at 280°C in split about 100:1 with an amine‑deactivated liner, then a 2 min post‑desorb bake each run to clear carryover. , siloxanes — pre-bake a new fiber in a spare inlet through a short guard column with the split vent wide open; it knocks the background down without dulling the trace hits from fabric singe or blood. @brianm54 is right about temp helping, but I’d only shorten extraction if you basify/salt the matrix (Na2CO3 + NaCl); can you do that on the blood set?
If carryover’s the pain, bump to SPME Arrow (DVB/Carboxen blend) for robustness and do a real bake‑out: 45–60 min at 290–300°C in high split with an amine‑deactivated liner, plus a 5‑min post‑desorb bake every run. For fabric singe residues, add a small K2CO3 crystal so your 60°C hold favors the free base and keeps water off the coating — my siloxane background dropped without losing the low‑level hits. @OP, are you on a low‑bleed septum with septum‑purge at least [redacted]/min?
the “fragile tip failures” on 65 µm PDMS/DVB got me too — switching the GC inlet to a Merlin Microseal plus high‑temp low‑bleed vial septa cut coring and knocked down the siloxane haze. I’m with @leahc88 on using amine‑deactivated hardware, and I also saturate the vial with Na2CO3 to free the amines so I can shorten the hold without losing the trace hits. Could you try the Microseal and add a about 2‑minute post‑injection backflush to clear carryover?
I’d drop HS temp to about 45–50°C — think gentle sauna, not hot yoga — and push vial chemistry: sat. NaCl plus a tiny NaOH flake so amines stay “free‑base” and jump to HS; that cut my siloxane haze and carryover without losing trace hits. I also do a quick pre‑run oven bake of the fiber (10–15 min, split vent open) and only engage the inlet once the baseline stops “breathing.” Would a PA fiber be enough for your targets, or do you truly need the DVB load?
I’ve had better luck moving to the 50/30 µm DVB/CAR/PDMS and swapping NaOH flakes for a saturated K2CO3 brine; carbonate keeps pH high without gnawing on septa/epoxy, which cut my siloxane haze and the tip drama. Also, a “wool-less SPME liner” helped — have you tried that?
Try keeping the 50/30 µm DVB/CAR/PDMS but add an inlet backflush with a short “bake-and-vent” after desorption: open split 100:1 and hold the inlet at about 285–290°C for 2–3 min before the next run — this cut my amine carryover without lifting the baseline. Pre‑silanized HS vials helped more than swapping septa in my hands. @grayson_lee92 did the carbonate brine still behave once you turned on backflush?
If the tip breakage is killing you, move to SPME Arrow with the mixed carbon/sorbent layer — it’s way less ‘toothpick‑like’ — and pair it with a Merlin Microseal; our background siloxanes dropped and the light amines stayed put, and @jennifer_wright57’s carbonate brine plays nice with it. Do you have Arrow tooling on your autosampler?