The pH of tobacco smoke

The pH of tobacco smoke is a determining factor in its acute toxicity. With a rise in pH above 6·2, the smoke contains increasing amounts of unprotonated nicotine, the most toxic form of this agent. The pH was determined by puffing smoke over a highly sensitive combination electrode. Measured were the pH of the total mainstream smoke of some domestic, foreign and experimental cigarettes, as well as of some cigars and little cigars. The pH of individual puffs of cigarettes made from Bright tobacco and blended tobacco decreased slightly, from pH 6·3 to 5·6, with increasing puff number. The pH of puffs of cigars and little cigars increased from about pH 6·5 to above 7·5. The pH of smoke from cigarettes made from Bright tobacco varieties increased significantly as the height of the leaf position on the stalk increased. Total nitrogen, total alkaloids and total volatile bases of the tobacco showed a high degree of correlation with the pH of the mainstream smoke. Data on sidestream smoke are also presented. The findings of this study are discussed with regard to tobacco-smoke toxicity and inhalability.