I don't think it's sodium hydroxide contamination, if you salted with sulphuric acid it's sodium sulphate. It's harmless but just as annoying if you want purity.
Yesterday I tried to purify my mescaline sulphate by dissolving in boiling anhydrous methanol. This should leave all anorganic salts behind. However, I discovered that it takes quite a lot of methanol since mescaline sulphate is only slightly soluble in it. For me this was not convenient at all (not enough methanol at home, no fume hood).
Next time I will try a second acetone bombing. Dissolve the whole lot in a minimal amount of water, add acetone and put in freezer. The mescaline should crash out, leaving anorganic salts behind. The downside is there is still some mescaline left in there that is not pure at all. Anyone know how much mescaline sulphate water at say -15 C can hold? Also, would all the inorganic salts in the water/acetone mixture prevent nice crystal formation?