Effect of temperature and humidity on the gas-particle partitioning of nicotine in mainstream cigarette smoke: A diffusion denuder study

During cigarette smoking, nicotine deposition in the mouth, upper airways and deep lung can occur via rapid diffusion of gas-phase nicotine and via deposition of particle-bound nicotine, with changing proportions, dependent on physical and chemical equilibria. We have used a diffusion denuder approach to physical equilibria to evaluate comprehensively the percentage of nicotine that is initially in the gas phase of mainstream cigarette smoke under different temperature (T) and relative humidity (RH) conditions. Smoking experiments with University of Kentucky 3R4F research cigarettes were performed at six denuder T values (291-335 K) and three RH values (30%, 45% and 60%). G/P partitioning of nicotine increased significantly with increasing T, and decreased substantially with increasing RH. The measured gas diffusion coefficient of nicotine in the system, D298K = 0.071 ± 0.006 cm2 s−1, was consistent with published data. Application of the theoretical denuder model of Lipowicz and Piadè indicated that the initial gas-phase fraction (fgLP) of nicotine entering the denuder tube ranged from ≈ 0.012% to 7.2% depending on T and RH. The fgLP values were used to derive the G/P partitioning constant, Kp, proposed by Pankow, ranging from 1.61e-06 to 1.06e-03. The first reported use of van't Hoff plots of Kp yielded an enthalpy change of 110 kJ mol−1, consistent with the thermodynamics of the solution process and the acid-base equilibrium of nicotine in droplets of mainstream smoke. These new data offer scope for improved modelling of nicotine behaviour in tobacco smoke and its subsequent deposition in the respiratory tract.