if its 91% and the 9% is just water, and you are dissolving pure freebase dmt, its fine, it will just take a little while longer to evaporate.
If there is more than just water in those 9%, thats not good. Or if you are trying to use the IPA to pull from, say, a mix of sodium carbonate+dmtfumarate or acetate that was freebased, than it will be a problem because the 9% water will pull some sodium carbonate and sodium fumarate (or sodium acetate) impurities.