The Form of Nicotine in Tobacco. Thermal Transfer of Nicotine and Nicotine Acid Salts to Nicotine in the Gas Phase

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Abstract
Thermal transfer to nicotine in the gas phase from neat nicotine, from various nicotine carboxylic acid salts, and from endogenous nicotine in Burley, Bright, and Oriental tobacco samples has been examined by thermogravimetric/differential thermal analysis/mass spectroscopy and evolved gas analysis. Under the conditions used in these studies, the peak transfer temperatures of these substances to nicotine in the gas phase are nicotine and nicotine acetate, both ca. 110−125 °C; nicotine malates, ca. 110−210 °C for nicotine to malic acid ratios of 1:0.56 and 1:1 and ca. 160−210 °C for a nicotine to malic acid ratio of 1:2; (S)-nicotine bis[(2R,3R)-hydrogen tartrate] dihydrate, ca. 195−210 °C; and tobacco samples, a range of ca. 160−220 °C. These results suggest that nicotine is mostly protonated in tobacco leaf. In all cases, the temperature of the transfer of nicotine to the gas phase was found to be many hundreds of degrees below the temperatures observed around the coal of a burning cigarette (smolder, ca. 500−775 °C; dynamic smoking, 600 to over 950 °C). Within the narrow zone of a puffing cigarette that encompasses an intermediate temperature range (125−250 °C), kinetic data suggest that these temperatures are not sufficient to volatilize significant amounts of nonprotonated nicotine, assuming any exists at all, during the short puff duration (2 s). It is concluded that nonprotonated nicotine and protonated nicotine (salts of nicotine with natural tobacco carboxylic acids) will transfer nicotine to smoke with comparable yields and efficiencies during the smoking process. Keywords: Nicotine; nicotine carboxylic acid salts; thermal transfer; gas phase; tobacco; thermogravimetric/differential thermal analysis; mass spectroscopy analysis; TGA/DTA/MS; evolved gas analysis; EGA; “bound” nicotine