I hope this is the right place for this question...

If I buy 91% IPA and dump x grams of anhydrous magnesium sulfate into it... can I get it to 99% since the other 9% is water? Or is this a non-chemistry guy pipe-dream?

Some of your MgSO4 will dissolve in your IPA, so you might be better off with another desiccant like silica gel (available as kitty litter, but would need to be ground very finely to be effective), KOH or molecular sieves. With any of these you can get it even drier than 99%.

MgSO4 is better for drying non polar solvents.



Here is a paper on drying solvents.

Thank you kindly