Automated determination of hydrogen cyanide acrolein and total aldehydes in the gas phase of tobacco smoke

For some time there has been wordwide concern for the health risks of cigarette smoking. In several countries, including the United States, Canada and the United Kingdom, surveys of the tar and nicotine delivered by commercial brands of cigarettes are carried out and published. Recently carbon monoxide levels have also been measured. The combustion of tobacco products such as cigarettes also produces three major ciliatoxic components, namely hydrogen cyanide (HCN), formaldehyde and acrolein ]. As in the case of tar, nicotine and carbon monoxide, the detection of statistically significant differences requires the results of from 10 to 30 analyses per brand per chemical parameter at several points in time; as a consequence, the use of automated chemical analyses is advantageous. Individual automated colorimetric methods have been published for HCN, acrolein and total aldehydes using AutoAnalyser II techniques; however, the simultaneous determination of all three from a single sample has not been attempted due, in part, to the fact that different gas scrubbing agents and diluents must be used for each analyte. Selection of a single efficient scrubbing agent and the introduction of on-line dilution facilitate the simultaneous determination of the amount of HCN, acrolein and total aldehydes (mainly acetaldehyde) delivered by various brands of cigarettes. This improves the overall laboratory efficiency and minimises the manual effort in the analytical methodology. Table 1. Estimates of precision from the automated determination of hydrogen cyanide, acrolein and total aldehydes in standard aqueous solution and in methanolic extracts of the gas phase from a Canadian reference cigarette.

HCN, acrolein and total aldehydes using AutoAnalyser II techniques; however, the simultaneous determination of all three from a single sample has not been attempted due, in part, to the fact that different gas scrubbing agents and diluents must be used for each analyte. Selection of a single efficient scrubbing agent and the introduction of on-line dilution facilitate the simultaneous determination of the amount of HCN, acrolein and total aldehydes (mainly acetaldehyde) delivered by various brands of cigarettes. This improves the overall laboratory efficiency and minimises the manual effort in the analytical methodology.  [4] and ethanol [5] for extracting aldehydes, HCN, and acrolein respectively, in similar applications. Temperature was maintained at 2 +_ 2 C using a circulating bath and 50% ethylene glycol. enylhydrazine to form substituted hydrazones which in turn produce coloured complexes with sodium hydroxide; acrolein is determined using the method developed by Cohen and Altshuller [5] whereby, in the presence of mercuric chloride and trichloracetic acid, acrolein condenses with 4-hexylresorcinol to give a blue complex. All three reactions are monitored colorimetrically.

Procedure
Figure is a representation of the manifold used for simultaneously measuring the three analytes. The twin sampling probe incorporated in the sampler is used to deliver the sample stream to the manifold. One probe delivers the sample for the acrolein analysis whilst the other supplies a two-way stream splitter from which a sample is drawn for determination of HCN and total aldehydes. On-line mixing and sub-sampling must be carried out effectively and reproducibly. Simple use of coloured solutions enables the efficiency of the mixing assembly, shown in Figure 2, to be checked visually. Since there is a tendency for air introduced on sample switching to become trapped in the sub-sampling well, bubbles must be removed prior to this point as illus sample and dilution stream and the solubility and density of the stream are important parameters which must be matched for the reactions involved and the inclusion of a mixing c0il just after diluent addition helps in this regard. For HCN the linear absorbance range of the colorimeter is 0 to 0.45 0D which corresponds to a level of 0 to 13 mg/kg. A similar range is also obtained for acrolein whilst the level for total aldehydes is 0 to 0.35 OD corresponding to 0 to 230 mg/kg.
A suitable standard solution for each of these analytes is used to adjust the data processing equipment which provides direct printout in concentration units. Once calibrated, the samples generated from the smoking machine can be analysed simultaneously for HCN, acrolein and total aldehydes with the results printed in the units /2g "per cigarette. Although the individual methods are simple adaptations of the published procedures the integrated system as illustrated is unique in utilising a single sample with on-line dilution and sub-sampling. In this way, maximum responses are obtained and the anticipated levels of HCN and volatile aldehydes are reduced to within the range required for linear colorimetric response.

Discussion
As already stated, the ability of the system to produce reliable determinations depends on efficient mixing and stable reaction chemistries.  months. With respect to the standard solutions, at first glance the precision appears to be somewhat greater than the level of 2 4% reported by others for analyses of this type [6]. However, it must be remembered that estimates of variance include day-to-day variations in colorimeter response as well as week-to-week variations due to standard and reagent preparation. The variability in the yields from the 'monitor' cigarette are still larger due to the additional component of between-cigarette differences as a result of the manufacturing process. Accurate analytical results for the gas phase deliveries of cigarettes can be obtained only if the trapping solution efficiently absorbs the analytes under examination. The data in Table 2 indicates that either ethanol or methanol held at 2 C can be used as a scrubbing agent for the extraction of HCN, acrolein and other volatile aldehydes.
Experiments using a second flask connected in series demonstrated that the level of carry-over was slight. The maximum transfer was 4% obtained for total aldehydes using a water solvent; the minimum level of 2.6% was obtained for acrolein using ethanol as the solvent. It is therefore concluded that approximately 95% of the theoretical yield of the analytes are collected by a single trap.