 Nicotine in tobacco smoke exists in either a protonated or unprotonated form, depending on the presence of natural acids and bases, the tobacco blend, tip ventilation, and the use of additives.Whereas protonated nicotine is positively charged and not volatile, unprotonated nicotine ("free-base nicotine") from tobacco smoke is volatile and readily passes into lipid cell membranes.More unprotonated nicotine in a puff delivers more nicotine to the brain.