hardware store acetone is sufficiently pure, usually >98%. the rest is likely water.
SWIM used it with san pedro extractions (recrystallization) to get significantly pure off-white crystals.
not sure about your other questions. swim's never tried it with dmt, though any trace water present shouldn't create any hassles. rest assured, store bought acetone is a suitable solvent.
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"Experiments are the only means of attaining knowledge at our disposal. The rest is poetry, imagination." -Max Planck