Doing the evap test on some Xylene, i have been getting a slight residue. It is just traces of a white substance. It's not oily. I had to hold this bowl to the light just right to be able to take a pic of it.
The two white smudges pointed to are the residue. The other white is wear on the bottom of the bowl, not a residue.
Lower smudge is most representative, I guess.
I evaped about 3/4 of this bowl full to get this.

https://imgur.com/G1mRjgO.jpg

So, is this a worry?

Problem is, that with Acacia confusa Naptha does not work well at all. NMT is not that soluble in Naptha and I need to use the Xylene to get the goo out.

This is the Xylene.

https://i.imgur.com/viHPgku.jpg

You do not need to evap the toluene or xylene, it is possible to salt out alks into acidic water and extract from it - just make the water alkaline again and filter out precipitated alks.

Without knowing what exactly the residue is, there's no way of answering that definitively. So, in the spirit of "better safe than sorry" the answer has to be: yes potentially.

I have to say though, it is a really small amount of residue from a pretty large amount of solvent. And it's quite possible that it didn't actually come from the solvent, but from the bowl (fatty fingerprint, residual soap, something like that).

Given that you probably want to freeze precipitate your crystals, maybe you can do a freeze test. Freeze a glass full of solvent for 24h, see if anything precipitates. If it doesn't, i think it should be ok to use (kitchen non-chemist here, to be clear).

Of course you could backsalt like doubledog proposed. Thing is, you're not really sure that the impurity doesn't still end up in your product. For that, you'd have to do yet another test (shake some solvent with acidic water, separate, base the water, make sure that nothing precipitates -- choose your acid and base such that they don't produce a salt that's insoluble in water).

Thanks for your answer.
It seems even less now as if it might evaporate to an extent.
Are impurities which people find generally an oily substance?

I didn't know you could freeze precipitate Xylene. Is there a difference in hot and cold solubility with DMT and NMT with Xylene? Freeze precipitating, I'm guessing, would always reduce impurities in the final product.

I tried dissolving my goo in Naptha to freeze precipitate and it did not completely dissolve.

I wonder if there is an easily obtained solvent which is not miscible in water which will dissolve DMT and NMT. I could water wash. Maybe I'll water wash some of this Xylene and then do an evap test. TBH however, I'm fine tuning things with the Xylene so as to handle and breathe it as little as possible. It's nasty stuff.

Oh. Yeah maybe you can't. I've never used xylene...

If you can't freeze precipitate, i think backsalting is preferrable to evaporation, as it preserves your solvent for reuse and removes many impurities from your product. Precipitation in water has been a bit tricky for me though. One could also go from the backwash back to a minimal quantity of xylene and evaporate that.

If freeze precip is an option, it would be my preferred choice.

Maybe someone smarter than me will chime in with info on freeze precipitating NMT and DMT in Xylene. One issue I have is trying to do all this without a PH meter. TBH, I have a small amount of AC and MHRB and don't plan to continue this once it's gone. At that point, other explorations will suffice, I think.

Freeze precip does not work with xylene. That's one of the main reasons why FASA methods were developed.

If your white residue slowly evaporates, there's a fair chance it might be naphthalene. Does it have a detectable odor? Naphthalene has a "mothball"-like odor, somewhat similar to impure DMT. Other possibilities are durene (1,2,4,5-tetramethylbenzene), penta- and hexamethylbenzene, all of which are described as having a "sweetish" odor. These methylated benzenes are relatively non-toxic, but naphthalene is best avoided.

It's still possible to clean up the material after isolating from the xylene and those processes fall under the FAQ.

I knew you'd chime in with a definitive answer. Thanks.
So, Sodium carbonate washing? No PH meter required.

You've been a huge help to me.

You'll have to be more specific. What are you planning to wash with sodium carbonate? It won't remove naphthalene from xylene, nor from DMT freebase recovered from xylene by evaporation.

Well, I went to the FAQ on "washing spice" and found...

"Have your product still in the solvent, before evaporation/precipitation. If you have already in crystal form, redissolve in a naphtha/heptane/hexane.
Add anywhere in between a pinch to 5 grams of sodium carbonate (yes, doesnt matter... All that is necessary is for it to be a basic solution) to 100ml clean water.
Add your spice-containing solvent and the sodium carbonate solution together in a container. Mix/shake/whatever (emulsions will not form).
Separate the solvent from the sodium carbonate solution using pippette/turkey baster/syphon/separatory funnel. One can repeat steps 2-4 if desired, but not strictly necessary
Freeze precipitate or evaporate to retrieve your DMT"

Which is similar to what I already do except it includes basifying the water first.

I might be being to worried about that small an amount of residue. What do you think?
I do want to keep the goo since NMT can be oily/gooey. Or is that correct?

Just don't evaporate the xylene - recover the product from the xylene by using some kind of acid. Otherwise you'll have to clean it up with a re-x from naphtha or heptane (assuming there's a possibility that the residue is naphthalene), and you say you'd like the goo to remain as goo.

While I have your attention, and hopefully haven't been too pesky, what is the purpose of the step of adding salt that I see in some teks?

Higher ionic strength pushes more DMT into the nonpolar phase.

Another case is where NPS is washed with saturated brine, which is a method of removing water from the NPS.

So, it depends how and when the salt gets added!