Hello
@Slimk123 .
Over here in the States, we tend to purchase all of our DIY ingredients separately; PG, VG, flavors and nic. The first three can reasonably be stored for at least a couple of years when stored in a cool dark place like a cupboard. The best way to store nicotine would be to transfer it into a glass bottle without too much air space and set it into the freezer. Folks here have done that with years, if not a decade, with excellent results. Next choice would be the fridge, which would be good for maybe up to a year or so.
I usually have 60 mgs in fridge at all times for mixing. We call that
working nic.
If you decide to take either of those routes with your nic, be sure to set it out and let it get to room temperature before mixing to insure no condensation is added to your mix.