The real value of using isopropanol is related to the variation in water solubility in 100LL. In a typical scenario, you fuel in a relatively warm location and fly into a much reduced temperature (i.e. at altitude and/or to the frozen north). As your warm fuel cools, water present in the fuel will come out of solution. If it's well below freezing, ice crystals can form in your fuel in sufficient quantity to blind your fuel screen. The real value of adding isopropanol is not so much to scavenge free water in your tanks (you should drain essentially all of that water out pre-flight), but to remove the additional free water as your 100LL cools, to prevent ice crystal formation.
I'm no chemist; I'm a ChE who has managed isopropanol by-product production and storage. Currently have only about 300,000 lb left, since this plant is shutting down. I use the red bottle (Iso-HEET), essentially pure IPA. Do NOT use the yellow bottle, which is a blend of methanol and water!
PS -