Chromatography Forum

Hi everyone,
is there anyone out there who has had much experience with using manual SPME with a merlin microseal?

After a few injections I have been getting problems with reproducibility (large sample loss), the 'duckbill' on the seal seems to abrade quickly and there are sometimes CO2 ion fragments in my mass spec which make me think I had an air leak at the time of injection. (Not to mention the suspicious 'pish' sound that it makes when I put the needle in and out.)

I use an SPME liner and inject in splitless mode. The SPME needle is left in the inlet after the purge vent opens for the duration of the 12 min run to condition it. The SPME needle is blunt-tip, 23 gauge.

I am currently trying samples using a standard septum which seems to be working fine and just wondering whether anyone else has had problems with the merlin?

cheers
Liz

I have never used a Merlin microseal, but I have noticed that the front edges of SPME needles can be very sharply squared off, which chews septa. Some very careful polishing with very fine abrasive sheets or stones can fix this.

Peter

what grit size? 8000 be OK? I don't want to create another septum wear-point by accident.

I actually wonder whether its just a problem with the way the standard Merlin wears, our old high pressure Merlin doesn't seem to have given the same problems with reproducibility.

Grit sizes on abrasives are a bit of a minefield, but 8000 sounds pretty fine. If you can get one the finest grade of diamond or ceramic knife hone is better than ordinary "wet or dry" abrasive paper. The green polishing sheets that used to (still do ?) come with Agilent MS toolkits are also good. You are aiming just to take off the very outer corner, not to reprofile the whole tip. Do a few light strokes, check with a lens or stereo microscope, do a few strokes etc.

Peter