| Abstract
| - Solution 1H NMR (proton-NMR) spectroscopy was used to measure the distribution of nicotinebetween its free-base and protonated forms at 20 °C in (a) water; (b) glycerin/water mixtures;and (c) puff-averaged “smoke” particulate matter (PM) produced by the Eclipse cigarette, aso-called “harm reduction” cigarette manufactured by R. J. Reynolds (RJR) Tobacco Co. SmokePM from the Eclipse contains glycerin, water, nicotine, and numerous other components. SmokePM from the Eclipse yielded a signal for the three N-methyl protons on nicotine at a chemicalshift of δ (ppm) = 2.79 relative to a trimethylsilane standard. With αfb = fraction of the totalliquid nicotine in free-base form, and αa = fraction in the acidic, monoprotonated NicH+ form,then αa + αfb ≈ 1. (The diprotonated form of nicotine was assumed negligible.) When the threetypes of solutions were adjusted so that αa ≈ 1, the N-methyl protons yielded δa = 2.82 (Eclipsesmoke PM); 2.79 (35% water/65% glycerin); and 2.74 (water). When the solutions were adjustedso that αfb ≈ 1, the N-methyl protons yielded δfb = 2.16 (Eclipse smoke PM); 2.13 (35% water/65% glycerin); and 2.10 (water). In all of the solutions, the rate of proton exchange betweenNicH+ and Nic was fast relative to the 1H-NMR chemical shift difference in hertz. Each solutioncontaining both NicH+ and Nic thus yielded a single N-methyl peak at a δ given by δ = αaδa+ αfbδfb so that δ varied linearly between δa and δfb. Since αfb = (δa − δ)/(δa − δfb), then δ =2.79 for the unadjusted Eclipse smoke PM indicates αfb ≈ 0.04. The effective pH of the Eclipsesmoke PM at 20 °C may then be calculated as pHeff = 8.06 + log[αfb/(1 − αfb)] = 6.69, where8.06 is the pKa of NicH+ in water at 20 °C. The measurements obtained for the puff-averagedEclipse smoke PM pertain to the chemistry of the smoke PM as it might be initially inhaledat 20 °C. Upon inhalation, the volatilization of nicotine and other acid/base active compounds(as well as a warming toward a body temperature of 37 °C) will alter the pHeff value of thesmoke PM during the time that it resides and ages in the respiratory tract.
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