CONVERSION OF NICOTINE IN TOBACCO-SMOKE TO ITS VOLATILE AND AVAILABLEFREE-BASE FORM THROUGH THE ACTION OF GASEOUS AMMONIA

Ammonia-forming compounds are routinely added to cigarette tobacco. Th e U.S. Food and Drug Administration (FDA) has argued that this is done to promote the formation of the volatile free-base form of nicotine i n mainstream smoke (MSS) particles, thus increasing its availability t o the smoker. The presence of ammonia in tobacco smoke may also be exp ected to promote the volatilization of nicotine from environmental tob acco smoke (ETS) particles in indoor air. The gas/particle partitionin g of nicotine can be parameterized in terms of the gas/particle partit ioning constant K-p = C-p/C-g, where C-p (ng/mu g) is the concentratio n in the particle phase and C-g (ng/m(3)) is the concentration in the gas phase. The ability of ammonia to increase the amount of nicotine i n the gas phase, as compared to the particle phase, was measured and c onfirmed. A gas-phase ammonia pressure of p(NH3) Of similar to 100 x 1 0(-6) atm (100 ppmV) was found to reduce the K-p value for the partiti oning of nicotine to tobacco smoke particulate matter by more than 100 -fold. The agreement between ETS and MSS at p(NH3) approximate to 100 ppmV was excellent, suggesting that the overall physical properties (e .g., polarity and number-average molecular weight) of ETS and MSS part iculate material are very similar. Because gas-phase nicotine deposits more readily in the respiratory tract than does particle-phase nicoti ne and because free-base nicotine is more lipid soluble than is proton ated nicotine, such a reduction in K-p will increase the availability of nicotine from MSS as well as from freshly formed ETS particles. At 20 degrees C and a relative humidity of 60%, the partitioning constant for the free-base form of nicotine is estimated to be K-p,K-fb = C-p, C-fb/C-g = 10(-4.94). Correction to a body temperature of 37 degrees C yields K-p,K-fb = 10(-5.97). Calculations using this K-p,K-fb value i ndicate that about 25% of the nicotine will be in the gas phase at a t emperature of 37 degrees C for inhaled MSS under the full ammonia effe ct at a total suspended smoke particulate matter level of 3 x 10(6) mu g/m(3).