In general, evaporating liquid solutions to make them more concentrated, or even to dry them out completely, works just fine. I've done this personally with 2Cs before, to liquid measure doses and then evaporate off to put in gelcaps. Unless either white vinegar or AMT has some rather unusual physical property I'm unaware of, I'm pretty sure this would work just fine. You'd end up with the same amount of AMT you started with, in less liquid.
The fastest way to evaporate small amounts of liquid, in my experience, is to pour it into a shallow container and have a fan blowing over it. Since you only want to evaporate some of the liquid rather than all of it, and it's such a small amount, you could probably skip the shallow container and just use a shotglass or something.
Two other things to keep in mind:
-I have no idea what the maximum concentration of AMT in water and/or vinegar is, but if you evaporate enough of the liquid you'll pass the saturation point and some of the AMT will precipitate out of solution into solid flecks.
-If you evaporate down to such a tiny amount like 1mL, then getting all of it back *out* of whatever container you evaporated it in might be a bit of a trick. Just a tiny bit of liquid sticking to the edges of the glass could be a significant difference in dose once you get it that concentrated.
Of course, worst case, you could add some more water to dilute it again if either of those problems comes up. Just things to keep in mind to avoid some potential hassle and frustration.
