I don't want to clog this important thread with DIY stuff, but I thought I would jump in briefly for those wondering about how to store nic long term. My thoughts on this matter have changed a bit from what I "knew" years ago, but not much, and not in my methodology.
I have unthinned VG-nic in well-sealed glass in the freezer that is virtually unchanged after 6.75 years. In plastic, especially LDPE, it will oxidize, even in the freezer. Some PG-nics I've had in glass did oxidize in the freezer after about a year, some didn't. I don't vape PG-nic, nor have I had any for a few years, so I don't have more data on that, but it seems that the cleaner the nic, the longer it will freeze unchanged in PG. I think others here (Salem?) has found this too. Most nic today is very clean compared to 2009.
I don't have data on frozen ready-to-vape e-liquids with flavors, since I make my own fresh as I need them. I don't buy flavored e-liquids, and I only freeze unflavored VG-nic, mostly 100 mg/mL.
If you feel better by purging the headspace air with N2 or Ar to rid it of O2, ok. However, I think it is a negligible effect. 3 mL of headspace air at 25% O2 will give enough O2 to at most react with about 5 mg of nicotine. And that is only if it all reacts. VG naturally contains about 2 mg of O2 per liter, which if it all reacts will oxidize about 0.38 mg of nic...per liter of VG.
If the nic started out colorless before freezing, and it remains colorless, it has not oxidized. Nic-oxides are deep brown colored, and it takes barely any at all to yellow a nic solution. It takes considerable coloration before the original nic concentration is significantly impacted...although you may detect a tobacco taste and added TH. Testing is fine if you want to do that, but no color change means no oxidation. And kit titrations are really only accurate to about +/- 10%. 10% oxidation will be a very deep orange-brown. I used to test, I just use color now.
Cold slows all reactions down, frozen solid or not (VG does not freee entirely). This is a function of chemical kinetics and molecular dynamics...nic and O2 cannot move well in the thick glue-like liquid that VG turns into in at freezer temps, so they don't find each other as easily. And since the only real source of O2 that can impact nic is from the external environment, well-sealed glass takes care of that. Plastics tend to be rather O2-porous.
Yes, very cold VG will absorb water from the air, but again, this is a negligible effect. VG is too thick to syringe or work with very cold, anyway, so allowing it warm to room temp before opening is normal.
Making diluted unflavored nic with added water will introduce more O2, but probably very little. Viscosity is lower, however, so nic cycles to the surface more often...but again, if it is sealed in glass, I doubt the effect after a long time in the freezer will be noticeable. I don't do this, however, and I don't have concrete data on this.
Cold VG will expand when warmed, so I advocate a few mL of headspace. Let the bottle warm standing up...that air bubble will expand more than VG and can cause leaking under the cap if the bottle is on its side and in a warm environment.
I use SpecialtyBottle.com 50 mL Eurodropper amber bottles (
Essential Oil Amber Dropper Bottles | Specialty Bottle). This is a company that makes glass for chemicals, so it is not cheap glass with many defects that can crack with temp change. I've never had a break, but I'm not saying it is impossible. Glass is glass. The dropper insert protects against spilling and allows syringe access to the liquid. Others use glass bottles with cone-caps for good sealing. They have blue and green glass as well. Dark is good, but it is UV that catalyzes oxidation most, not so much visible light, and freezers are dark. I have some of my nic in colorless glass bottles, and they have not changed in the freezer in the years I've had them, maybe 4 years...and even at room temp, oxidation is very very slow if in well sealed glass. A 50 mL bottle out for usage will last me months of mixing with very little change.
I have every reason to believe VG-nic will last essentially forever unchanged in the freezer and in glass. If 6.75 years shows no change, I don't see at all why it shouldn't last for decades.
