The Pyrolysis of Tobacco Additives As A Means of Predicting Their Behaviour in A Burning Cigarette

In order to understand the behaviour of tobacco additives in the burning cigarette it is important to know whether they transfer intact to the smoke or whether there is any decomposition during smoking. There are practical problems in comparing the chemical analysis of whole smoke from cigarettes with and without additives. Changes to the smoke chemistry may be insignificant in analytical terms and therefore missed from a general scan. Targeted analysis of key components potentially overcomes this concern, but has the drawback of being expensive in terms of time and analytical resources. Pyrolysis-GC-MS is an attractive solution in that it potentially enables the effects of combustion of a single material to be studied in isolation. However, it is not entirely valid to base an assessment of a material on a pyrolysis experiment alone unless the results can be demonstrably related to the cigarette smoke chemistry. The variables that affect the outcome of combustion are temperature, rate of change of temperature, oxygen concentration and chemical environment (matrix and gas phase). The key to this work has been in performing pyrolysis experiments under a range of different conditions and relating the experimental conditions to those within the burning zone of the cigarette to give a prediction of smoke chemistry. To test the theory in practise, the transfer and the extent of degradation of anisole, p-anisaldehyde, benzaldehyde, isoamylisovalerate, methyl trans-cinnamate and vanillin within a burning cigarette were investigated using this pyrolysis method. Pyrolyses were undertaken on each additive at 14 sets of pyrolysis conditions: temperatures between 200°C and 700°C in 2 % and 10 % oxygen, and at 800°C and 900°C in 2 % oxygen. By monitoring the presence of the intact additive in the volatile components from the pyrolysis, the temperature at which the additive is likely to transfer to the smoke was determined. By monitoring the decomposition products at temperatures up to this transfer temperature, the extent and products of decomposition likely from the additive were estimated. The pyrolysis predictions were compared with results from a previous study involving adding 14C-analogues of the materials to cigarettes and measuring the resultant radioactive species in the smoke. The results from the pyrolysis experiments lead us to make the following predictions: Anisole, isoamylisovalerate and vanillin will transfer intact to the smoke at 200°C. p-Anisaldehyde and methyl trans-cinnamate are likely to transfer to the smoke at a higher temperature of around 400°C leading to some decomposition/oxidation (3 % and 1 %, respectively). Benzaldehyde is likely to transfer to the smoke at 200°C, but at this temperature a significant amount (~26 %) oxidises to benzoic acid. Both compounds appear resilient to further degradation at higher temperatures. These levels of transfer were found to be consistent with smoke chemistry data.