I'm running water samples for D and O using 2-mL vials in our GC PAL
autosampler. Because some of my samples are smaller than 2mL, I would like
to use inserts to avoid headspace. After searching the archives here, I
found the Sigma-Aldrich website, but I'm not sure which insert is best. What
are the benefits/reasons for an insert with a bottom spring or a polyflange?
Could someone please offer any advice, suppliers, and/or product numbers? 

Thank you!

Alison Sloat