my opinion, which is definitely not shared by all, is that difference in purity makes no difference in effects. I think its mostly self-suggestion, so people think its impure and then have a bad experience, or whatever.. The only way to truely test this is in a double blind test, because otherwise its all interesting anecdotal reports but not really definite evidence. Another thing that might affect is that impurities can be harsher on the lungs, and since external stimulus affects the experience (like the pain sensation in the throat/lungs), then people might have a worse experience or whatever.
What I said above is mostly about naphtha/hexane/heptane-extracted alkaloids.. When one talks about more polar solvents like limonene and toluene/xylene (yuck!), then there are other alkaloids involved, so the trip might be different. But still, I would also like to see double blind tests done. SWIM definitely preffers the limonene stuff, but not necessarily because the full-range alkaloids extracted with it a priori will create a better trip, but more because his conscience feels much better already when using food-safe and more natural products than petrochemicals, and this in turn is in a way paid off with the tranquility that tends to make his trips better. He hasnt noticed a pattern of effects specific to limonene-extracted stuff as compared to naphtha extracted stuff, not because there arent differences (there might be), but more because there are so many variables involved as mentioned above and because the dmt trips are always soooooo amazingly astonishing and mindboggling to him, that he cannot really compare, even two trips from the same batch.
Lastly, its important to note that 'impurities' can be a bunch of thing so its hard to define it all in one category.. we might be talking about dmt n-oxide, we might be talking about plant oils, etc.. So even if two people say 'they like the yellow stuff better' or whatever, they could be vaporizing very different things. In any case I think that, health-wise, people should specially avoid any solvent remains in their product.
but yeah thats just my opinion
