I was thinking about the clean up step in the FASA process, and the act of removing acetone from your solvent of choice. I always wash my solvents with liberal amounts of water until the water smells "clean". To me, the acetone/fumeric acid/water solution will smell almost minty until the solvent is clean. This usually requires quite a bit of water to get the job done. I'm curious what happens if one doesn't eliminate all of the acetone from the solvent.

Searching online, I found that acetone transforms into mesityl oxide and then to form isophorone when it comes in contact with lye. I don't know anything about these chemicals, but a quick google search shows that they are suspected carcinogens, and can cause kidney, liver, and neurological damage. I then searched for solubility, and I think these are very soluble in NPS.

I could be getting myself worked up over nothing, but I'm concerned about the potential unwanted toxic chemical reactions ending up in DMT. I'm definitely not a chemist, but I wonder if this should be a concern if all of the acetone is not removed from the NPS before returning the solvent to the lye solution.

You can stop worrying about the formation of mesityl oxide and isophorone. Because those actually need special conditions to form in large amounts (water free). And also the adduct of acetone to acetone is unstable and will split apart on its own.
And all these compounds are also volatile and will just evaporate while drying.

Also many of these complex alcohols and ketones occur in large amounts in naturally fermented alcohol or similar things (kombucha) and while you dont want to drink large amounts of them they will not be dangerous in the amounts that you will find them here.

I wouldnt let pure acetone sit over base for a long time because the longer you leave it the bigger the condensation product gets and once it reaches a certain limit its no longer volatile so you actually get a solid polymerised product that will contaminate your product.

You probably looked at reaction mechanism where they actually only use "normal arrows" and not the arrows that show the back reactions.

Thank you. Your detailed response really settled my fear.

I have another question about related to this. Given the saturation point of acetone in water, how much water does it take to truly remove all of the acetone from an acetone/xylene mixture? I've alway rinsed xylene with copious amounts of water multiple times until the water smells "clean". It takes quite a bit, and I'd like to tackle this more strategically if possible. Admittedly, I probably use more FASA than is needed.