It is uncertain which smoke toxicants are the most important in the various diseases associated with smoking but we are carrying out research to try and prioritise these toxicants. The aim is to focus on the most biologically relevant constituents of smoke and reduce the amount found in cigarette smoke, which will give us the best chance of succeeding in our technology development.
More than 5,000 smoke constituents have been identified in cigarette smoke and around 150 of these have been identified as smoke toxicants with biological activity.
Over the last 20 years researchers and public health organisations have drawn up toxicant lists comprising sub-sets of these constituents - the most widely cited being the ‘Hoffmann Analytes’ list of 44 constituents .
The Hoffmann analytes and their ISO mainstream yields for a 2R4F reference cigarette from University of Kentucky can be found below .
|Group||Analytes||Molecular Weight||Average Yields|
|Aromatic Amines||1-Aminonaphthalene (ng/cig)||143||15.1|
|Carbonyls||Methyl ethyl ketone (μg/cig)||72||62.72|
|Polycyclic Aromatic Hydrocarbon (PAH)||Benzo[a]pyrene (ng/cig)||252||7|
|Hydrogen Cyanide (μg/cig)||27||109.2|
|Nitric Oxide (μg/cig)||30||223.41|
|Carbon Monoxide (mg/cig)||28||11.96|
|Volatile Hydrocarbons||1,3-Butadiene (μg/cig)||54||29.94|
|Nitrogen Heterocyclics||Pyridine (μg/cig)||79||7.02|
|Metals & Metalloids||Arsenic (ng/cig)||75||10.4|
|Tobacco Specific Nitrosamines (TSNAs)||NAB (ng/cig)||191||16.3|
In recent years the ISO machine smoking regime has been criticised for underestimating the actual exposure of individuals to smoke from cigarettes, leading some researchers to use more intense smoking regimes in exposure studies.
No machine smoking regime can possibly predict exposure in all smokers so at British American Tobacco we typically use several regimes to measure the toxicant yields of a reduced toxicant prototype, including the Health Canada Intense regime.
We have studied the influence of different smoking parameters on smoke and constituent yields using methods originally developed to analyse our conventional products.
Below is a table of different machine smoking regimes .
|ISO Method||Massachusetts||Canadian 'Intense'|
|Puff volume (cm3)||35||45||55|
|Puff frequency (s)||60||30||30|
|Puff duration (s)||2||2||2|
|Vent blocking (%)||0||50||100|
Using these methods we have examined the effects of cigarette components and design parameters on yields under different smoking regimes, allowing us to predict toxicant yields from different cigarette design parameters .
A recent review identified the role of alternative smoking regimes in influencing overall smoke and individual toxicant yields, using study data from 1997 to 2006 .
Briefly, mainstream smoke yields as measured by smoking machines increase as larger puff volumes, more frequent puffs are taken, or filter vent-blocking is applied to highly ventilated cigarettes. This is largely the result of more tobacco being consumed during a puff to form mainstream smoke. Many possible changes may occur within the burning cigarette as the cigarettes are smoked with different smoking regimes. However, the extent of the change to the mainstream smoke composition, as contributed from various smoke formation mechanisms (combustion, pyrolysis, pyrosynthesis and direct transfer) has not been systematically studied.
The availability of robust and reliable analytical methods are the key to measuring - and in turn reducing - smoke toxicant yields from reduced toxicant prototypes.
Accurately measuring and removing smoke toxicants has posed significant technical challenges, partly due to;
The difficulties of reliably measuring smoke toxicant yields were reported in a cross-industry, joint-sponsored study of the Hoffmann analyte yields from cigarettes on sale in the UK . This study illustrated the challenges in developing analytical methods for smoke toxicants and the presence of significant inter-laboratory differences in yields.
Our analytical scientists continue to refine methods to measure toxicant yields by reviewing and modifying our analytical methods. We have recently detailed our approaches to the determination of pyridines  and aromatic amines  as well as general issues around chromatographic sample preparation . We have actively participated in cross-laboratory method assessment activities to ensure that our methods are as accurate and reliable as possible [2, 5].
There have been suggestions that free radicals in cigarette smoke may play a role in the development of smoking related diseases. Although evidence for this is currently limited, we seek to understand the relevance of these agents to disease processes.
As a first step we developed reliable analytical techniques for quantifying free radicals in smoke [9-15], indicating that there are 1014 – 1015 spins per cigarette in the gas phase of smoke. In short, we developed a spin-trapping methodology, in which it is possible to measure shortlived free radicals in both the gaseous and particulate phase of mainstream cigarette smoke. By spin trapping the gas phase free radicals, the oxidation products derived from the corresponding spin trap can be clearly seen by EPR ( Electron Paramagnetic Resonance) spectroscopy.
Since then we have begun to identify the free radicals formed in smoke and different types of spin traps have been used to trap different transient gas-phase radical species [10-16]. We have also observed carbon and oxygen-centred gas phase free radical species and quinonic radicals in the particulate phase of cigarette smoke. However, it remains a very challenging task to distinguish the toxicological potential of free radicals generated in smoke from those of the other known toxicants.
Minimising the influence of sample ageing and artefact formation on toxicant yields is a major research challenge in this area.
A second challenge is to develop methods for analysing toxicants on a time resolved basis and on time-scales relevant to their formation. This is essential if we are to relate toxicant yields to the mechanisms involved in their formation.
Below is a single photon ionisation (SPI) time profile of propyne (40m/z), acetone (58m/z) and isoprene (68m/z) recorded during the smoking of a Kentucky 2R4F reference cigarette .