The available evidence suggests that most of the nicotine in mainstream tobacco smoke is in the smoke particle matter (PM) phase. Nicotine can exist in protonated and free base forms in the smoke PM, and alpha(fb) is the fraction of the PM nicotine that is in the free base form. Because only the free base form can volatilize from the smoke PM phase to the gas phase of an inhaled aerosol and because gaseous nicotine deposits rapidly in the respiratory tract (RT), the magnitude and rate of nicotine deposition in the RT will depend on alpha(fb). The types of values that alpha(fb) can assume in the PM of cigarette smoke aerosols have not been well-known. The conventional view has been that mainstream cigarette smoke PM contains relatively little free base nicotine so that the cigarette smoker must absorb nicotine mostly from deposited particles. A prior study concluded that because cigarette smoke is at "pH 5.3", there is very little free base nicotine in such smoke. A 1994 internal tobacco company document discusses the view that "smoke pH" values for cigarette smoke are "approximately 6.0". This work uses volatility-based measurements to provide determinations of equilibrium nicotine alpha(fb) values for mainstream smoke PM from selected cigarettes. The effective pH (i.e., pH(eff)) of the smoke PM from selected brands of commercial cigarettes was found to span a range of 6.0-7.8 (nicotine alpha(fb) = 0.01-0.36), with all pH(eff) values much larger than 5.3 and most larger than 6.0.

Tobacco smoke contains thousands of chemical compounds, including many carcinogenic polycyclic aromatic hydrocarbons (PAHs). To determine the concentration ranges of PAHs in tobacco smoke and to understand what factors alter their levels, we quantitatively measured 14 PAHs in mainstream smoke from a transnational U.S. brand (Marlboro) and from locally popular brand cigarettes from 14 countries. We used standardized machine smoking conditions (35-mL puff volume, 60-s puff interval, and 2-s puff duration), extraction of total particulate matter from the Cambridge filters, and gas chromatography/mass spectrometry detection. Deliveries of total PAHs in mainstream smoke of local brands were statistically significantly higher (p < 0.01) than Marlboros in seven countries. In four countries, Marlboro cigarettes had mainstream smoke total PAH levels that were statistically significantly higher (p < 0.01) than local brands. In the remaining three countries, the differences in PAH levels were not statistically significant. Under standard machine smoking conditions, PAH levels were negatively correlated with cigarette filter ventilation levels. We found that several local brands containing primarily flue-cured tobacco filler had relatively high mainstream smoke PAH deliveries, in agreement with findings by previous researchers that flue-cured tobacco typically delivers more PAHs than other tobacco types. We also observed that PAHs were inversely correlated with total carcinogenic tobacco-specific nitrosamines and nitrate content, but these correlations were not statistically significant at the 95% confidence interval. The findings suggest that tobacco blend and nitrate levels may influence PAH deliveries, but other factors may confound this relation.

We believe that this method provides excellent versatility and throughput for the estimation of mouth-level exposure to a wide range of toxins in cigarette smoke under naturalistic conditions. In addition, this method allows a far more accurate measure of exposure both from a single cigarette as well as from daily smoking.

Mainstream tobacco smoke (MTS) was collected from Camel and Marlboro cigarettes for the determination of the delivery levels and equilibrium gas/particle partitioning constants K(p) (m(3) microg(-)(1)) of 26 volatile organic compounds (VOCs) of toxicological interest. K(p) values are important for understanding the fractional distribution of each compound of interest between the gas and the particle phases of MTS. The experimental method involved (i) drawing a smoke sample into a Teflon sampling bag at 20 degrees C, (ii) allowing the smoke particulate matter (PM) to collect on the walls of the bag, (iii) sampling the bag to determine the initial gas phase concentration of each VOC, (iv) removing the gas phase from the bag, (v) refilling the bag with humidified nitrogen gas, (vi) reestablishing the gas/PM equilibrium, and (vii) redetermining the gas phase concentrations. For each smoke sample, a comparison of the initial and redetermined gas phase concentrations allowed calculation of the total (i.e., gas + particle) delivery level (= m(tot), ng cig(-)(1)) and K(p) value (= c(p)/c(g)) at 20 degrees C for each compound, where c(p) (ng microg(-)(1)) = concentration in the PM phase and c(g) (ng m(-)(3)) = concentration in the gas phase. Significant deliveries were observed for a number of carcinogenic VOCs. For the Camel cigarettes tested, the average m(tot) values for 1,3-butadiene, acrylonitrile, and benzene were 10(4.6), 10(4.4), and 10(4.8) ng cig(-)(1), respectively; for Marlboro, the m(tot) values were 10(5.0), 10(4.6), and 10(4.7) ng cig(-)(1), respectively. For each of the 26 VOCs, the smoke PM from the two brands yielded very similar K(p) values at 20 degrees C. In addition, the vapor pressure-dependent K(p) values of the 26 VOCs were in close agreement with predictions made by the Pankow theory of absorptive gas/particle partitioning [Pankow, J. F. (1994) Atmos. Environ. 28, 185-188]. These results can be used in general predictions of chemical behavior in tobacco smoke, including deposition mechanisms and rates in the respiratory tract from inhaled MTS. Example calculations are provided to illustrate how the gas phase fraction at equilibrium (f(g,e)) increases strongly with increasing compound vapor pressure and temperature and with dilution of the inhaled tobacco smoke total PM concentration (microg m(-)(3)).