Free-base nicotine in tobacco products. Part II. Determination of free-base nicotine in the aqueous extracts of smokeless tobacco products and the relevance of these findings to product design parameters

Reports in the peer-reviewed literature and popular press have alleged that smokeless tobacco product (STP) manufacturers increase the addictiveness of their products by adjusting formulae to increase the relative percentage of nicotine in STP that is not protonated. Such nicotine is more popularly, but incorrectly, known as free-base nicotine (“FBN”) as it is a calculated amount as opposed to a real chemical species in the STP. Some regulators have mandated reporting of FBN as estimated by Henderson–Hasselbalch equation (“HHE”) using the pH-value of an aqueous suspension (or extract) of STP. This is technically incorrect because the HHE is only valid in pure dilute aqueous solution of a single base and its conjugate acid. The aqueous suspensions (or extracts) of STP often contain high concentrations of salts and polymeric anions such as pectate and many other compounds, and there is a molar excess of ammonia over nicotine in some products. These are heretofore-unrecognized sources of error in use of the HHE to estimate relative amount of nicotine that is not protonated results in inaccurate FBN-values. Thus, it is not surprising that attempts to show the relevance of estimated value of FBN in STP to human physiology have failed.