So I'm surprised this isn't already on here!
Drip Hacks sell WS-23 by the crystal. I purchased 10g.
This is what creates the 'Malaysian' effect of the ice cold liquid in things such as the famous Fantasi brand.
Mixed crystals at 10%, so I put 10g into 90ml of PG, heated ever so slightly in Luke warm water, shook, repeated, shook, repeated... this thing was a bugger to get completely dissolved.

Added it to a recipe at 3% and it absolutely blew my mind away and gave me complete brain freeze.

Caution is required when mixing with this - it's soooooo cold! I would never put more than 1% in any mix, and even then I'd let it steep for the coolness to settle as much as possible!

If you've got a fruity flavour, like koolada, or just like proper ice hits without the menthol, this is an additive you need to check out. You can also buy it pre-dissolved from places like Chefs Flavours etc..

Hope this helps!