Gas/Particle Partitioning Constants of Nicotine, Selected Toxicants, and Flavor Chemicals in Solutions of 50/50 Propylene Glycol/Glycerol As Used in Electronic Cigarettes

For an electronic cigarette (e-cigarette) aerosol with known total particulate matter concentration (TPM, mu g/m(3)), predictions of the fractions of some compound i in the gas and particle phases (f(g,i) and f(p,i)) at equilibrium can be made based on K-p,K-i (m(3)/mu g), the compound-dependent gas/particle partitioning equilibrium constant. f(g,i) and f(p,i) affect the modes and locations of deposition in the respiratory tract. K-p,K-i depends inversely on (1) the pure compound liquid vapor pressure (p(L,i)(o)), (2) mole fraction activity coefficient (zeta(i)) in the absorbing liquid, and (3) mean molecular weight of the absorbing liquid ((MW) over bar). K-p,K-i values were measured at 20 degrees C for 32 compounds as spiked into simulated e-cigarette liquids prepared as 50/S0 mixtures (by weight) of propylene glycol (PG) and glycerol (GL). K-p,K-i values at 37 degrees C were estimated. The 32 compounds were nicotine (in free-base form), seven toxicants (propanal, acetone, hydroxyacetone, benzene, toluene, p-xylene, and ethylbenzene), and 24 flavor chemicals (2,3-pentanedione (acetyl propionyl), isobutyl acetate, ethyl butyrate, butyl butyrate, isoamyl acetate, 2,3-dimethylpyrazine, 3-methyl-l-butanol, limonene, 2,3,5-trimethylpyrazine, p-cymene, benzaldehyde, (Z)-3-hexen-1-ol, menthol, 2-acetylpyrrole, benzyl alcohol, methyl salicylate, cinnamaldehyde, methyl anthranilate, (+)-aromadendrene, cinnamyl alcohol, methyl cinnamate, maltol, ethyl maltol, and coumarin). The measured log K-p,K-i values were found to be generally correlated with literature values of log p(L,i)(o); the scatter is caused by variation in zeta(i) between similar to 1 and similar to 1000. K-p measurements were attempted, but values were not reported for acetaldehyde, 2,3-butanedione (diacetyl), vanillin, and ethyl vanillin. Acetaldehyde was found to form significant amounts of its cyclic trimer and cyclic tetramer; for diacetyl, the evidence suggested significant amounts of reaction products, possibly hemiketals and ketals with PG/GL, and for vanillin and ethyl vanillin, the K-p values are large and accordingly more difficult to measure. f(g) values are calculated using a range of K-p and TPM values.