Wondering if it is possible to add acidified water to used naphtha and collect separated water then basify and collect freebase in naphtha. If so how much of the acid solution would be needed as the goal here is to concentrate it for precipitation?

I reuse naphtha without an acid wash. Haven't found a need to do it.

Besides being an extra step that I don't find is needed, an acid wash will remove any DMT that did not freeze precipitate from naphtha (~1mg/mg I believe, but can't find the reference so I could be wrong).

Oops, I think I understand better now. You don't want to reuse the naphtha, you want to concentrate the DMT without evaporating.

Hard to say if it would work. Depends on the partition coefficient. I just resuse the naphtha ok the next extraction.

The most definitive approach would be to conduct a test.

To a measured volume of naphtha, add a carefully measured amount of DMT freebase such that it will all dissolve at room temperature. Place this in the freezer and after the appropriate passage of time, collect, dry and weigh the precipitated freebase.

You now know how much freebase remains in the naphtha post freeze precipitation and can use that figure to calculate how much acid you'd need to use in order to recover it, how much base to add, and the minimum amount of fresh naphtha you'd need to pull it from the basic solution using three pulls.

By evaporating that naphtha you'll find out how efficient (and/or worthwhile) all this extra effort actually was.

You could just cut to the chase and evaporate some (i.e. a measured volume) of the used naphtha that you already have and use the amount of DMT obtained as a guide to the amounts of acid, base and fresh naphtha to be used in the recovery process which is essentially the same as the the test process outlined above.

At some point you have to either evaporate the naphtha (or another solvent...) or decide what to do with a little bit of DMT salt because, obviously, repeated freeze precipitations of ever decreasing size invokes the law of diminishing returns fairly early on.

As far as the arithmetic of how much DMT will react with how much acid, etc. I would urge you to look through the forum as this is something I've explained approximately 97 times during my time here at the Nexus (I know, I should have just programmed it as a macro button - I'm not that organised [world's worst chemist]).

I understand there are more than likely negligible amounts of dmt left after freeze precipitation but my theory is that if there is say 1500ml of used naphtha at that point all those negligible amounts will add up to at least a few hundred MG and trying to come up with a method to concentrate that to freeze precipitate it out. You commented on my other post about the solubility of dmt salt in acid solution and it is related to this. Essentially I'm trying to do an A/B extraction on the used naphtha and don't know proportions in order to do this. If I used slight excess of acid solution would it cause an issue with efficiently pulling the DMT free base back out of solution with naphtha after basifying again? Also do you know any reason that my theory of how this might work would be wrong. I'm willing to experiment because that's how we learn and I will post any data I find in case others may find informative but I don't want to waste my time if something is already known that would make this implausible

Yes, this is definitely viable approach, if there is any reasonable amount of dmt in the solvent.
Just make sure that you mix acid water with the solvent very thoroughly.

Indeed, using an excess of acid will not harm the DMT, it will just be slightly wasteful in terms of using reagents as you will also have to use more base to neutralise it. That's why I suggested an initial test so that you only have to use a slight excess of the acid, and consequently less base thereafter. OK, maybe acid and base are cheap at the moment but frugality is a desirable trait in my book.

People have done this before, it works, it's robust, and it's neither groundbreaking nor rocket science. Please have a look through the forum index (or indeed, the rest of the internet) to find out how you calculate reaction stoichiometry before coming back and asking very nicely about where you're having trouble with the equations and arithmetic which you've already laid out for yourself. I'm happy to help you if you're willing to meet me half way.