The carbonate wash is really just to mop up any residual Lye/NaOH; I doubt this will remove any impurities in the naphtha.
To do an evaporation test, simply put some of your lighter fluid onto a clear glass plate and let it evaporate naturally; when you inspect the plate once the naphthas evaporated you will see if any residue remians on the plate.
I am paranoid of my brain. It thinks all the time, even when I'm asleep. My thoughts assail me. Murderous lechers they are. Thought is the assassin of thought. Like a man stabbing himself with one hand while the other hand tries to stop the blade. Like an explosion that destroys the detonator. I am paranoid of my brain. It makes me unsettled and ill at ease. Makes me chase my tail, freezes my eyes and shuts me down. Watches me. Eats my head. It destroys me.