Determination of nitrogen oxides in the vapour phase of cigarette smoke: comparison of two methods
At present, the ISO TC 126 is tasked with working on a new ISO Standard ISO/NP 23924 “Determination of nitrogen oxides in the vapour phase of cigarette smoke under intense smoking conditions -- Chemiluminescence method”.
In the ISO document/NP 23924 it is defined that for the determination of nitrogen oxides (NO+NOx; as NOx) the gas phase of 170 puffs, 55 ml each (intense regime), is collected in a gas bag. After completion of the smoking run the amount of NOx is determined in the gas bag by using a chemiluminescence detector. NOx is known to be unstable over time, e.g. after sampling, therefore it is important to investigate the stability of the NOx in the gas bag during and after sampling. In the tobacco industry a different method to ISO/NP 23924 method for the determination of NOx is in use: the NOx concentration in the vapour phase is determined on-line by a chemiluminescence detector, so that for each puff and the entire cigarette a value for NOx can be calculated. Obviously, this detection principle would exclude the issue of aging the vapour phase with the potential impact on the NOx concentration.
In our study we compared the ‘gas bag’ against the ‘on-line’ method for the determination of NOx in the vapour phase of cigarette smoke. On a smoking machine type RM 200 A2 equipped with an online NOx analyser both methods are performed in parallel. While one part of the vapour phase is used for the online measurement, the remaining amount is collected as per ISO/NP 23924 in a prepared collection bag for determination of NOx after completion of the smoking run. To investigate the influence of time on the aging and therefore the concentration of NOx in the gas bag, measurement of NOx in the gas bag was carried out at different points in time after sampling.