Cigarette smoke is a complex aerosol containing a mixture of over 5000 chemicals in a dynamic state[1]. A number of these chemicals and vapour mixtures have been documented as toxicants such as the aldehydes, acetaldehyde and formaldehyde, and hydrogen cyanide (HCN)[2].
Filter additives such as activated carbon are general adsorbents and can be used for the non-specific filtration of vapour phase constituents in mainstream cigarette smoke. To minimise the cigarette smoke yields of specific toxicants, other filter materials have been investigated.
Here we discuss an ion exchange resin (Diaion® CR20), for the selective filtration of smoke aldehydes and HCN[3].
Ion exchange resins are highly ionic, covalently cross-linked, insoluble polyelectrolytes, supplied in granules or bead format[4]. These can be controlled or engineered with precision pore sizes and surface chemistries making them versatile, unique and adaptable. They are commonly prepared from styrene, with various levels of the cross-linking agent divinylbenzene, which controls porosity[4].
Diaion® CR20 (CR20) described here is comprised of 600 µm sized beads, with a moisture content of 15% by weight, density of 0.5 g/cm3 and total exchange capacity of 0.9 meq/cm3[5]. It offers the potential for the nucleophilic capture of aldehydes from mainstream smoke by forming imines (see equation (1) below), and due to its weakly basic nature it may also be used to remove HCN from the cigarette smoke (equations 2 and 3)[3].
Some examples of possible amine groups on the CR20 surface are shown below[3]:
CR20 was characterised using a variety of analytical techniques. Pore size and pore size distribution were examined using nitrogen adsorption at 77K and mercury porosimetry. To investigate the chemical composition and its surface functionality, Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron Spectroscopy, 15N Solid State NMR and water vapour adsorption were used[5].
The smoke data tabulated below shows filter additive performance (60mg of additive in a cavity filter) using a typical cigarette design[5].
To calculate the percentage removal efficiencies using CR20, a cigarette with an empty cavity filter was employed. As a control, cigarettes were made with filters containing 60mg of coconut based activated carbon (AC), which is typically used in some commercial products. Smoking was conducted under different smoking regimes (ISO in which one 35cm3 volume puff of 2s was taken every 60s, and Health Canada Intense (HCI) whereby one 55cm3 volume puff of 2s duration was taken every 30s). The table below shows % reductions for CR20 and activated coconut charcoal compared to a control cavity filter under ISO conditions. Data from HCI smoking conditions and comparisons can be viewed in the complete manuscript[3].
|
Smoke Analyte / Characteristics |
Filter additive - Activated carbon |
Filter additive - CR20 |
% reductions - Activated carbon | % reductions - CR20 | |
|---|---|---|---|---|---|
|
Cigarette puff No. |
7.0 |
7.1 |
7.0 |
~ | ~ |
|
Water (mg/cigarette) |
2.6 |
2.7 |
2.0 |
~ | ~ |
|
NFDPM (mg/cigarette) |
11.9 |
11.6 |
11.0 |
~ | ~ |
|
CO (mg/cigarette) |
11.2 |
11.5 |
11.1 |
~ | ~ |
|
Nicotine (mg/cigarette) |
0.93 |
0.94 |
0.90 |
~ | ~ |
|
Acetaldehyde (µg/cigarette) |
538.3 |
425.5 |
332.3 |
21 | 38 |
|
Acetone (µg/cigarette) |
269.7 |
181 |
265.2 |
33 | 2 |
|
Acrolein (µg/cigarette) |
62.8 |
39.2 |
37.4 |
38 | 40 |
|
Butyraldehyde (µg/cigarette) |
34.6 |
21.9 |
26.6 |
37 | 23 |
|
Crotonaldehyde (µg/cigarette) |
20.8 |
11.1 |
11.5 |
47 | 45 |
|
Formaldehyde (µg/cigarette) |
42.5 |
30.5 |
19.6 |
28 | 54 |
|
2-Butanone (µg/cigarette) |
62.8 |
38.3 |
54.8 |
39 | 13 |
|
Propionaldehyde (µg/cigarette) |
47.7 |
32.2 |
34.7 |
32 | 27 |
|
HCN (µg/cigarette) |
123.7 |
85.3 |
56.0 |
31 | 55 |
* NFDPM = Nicotine free dry particulate matter ('Tar').
* (%) = Percentage reductions compared to control cigarette.
As can be seen, the addition of the two filter additives had little effect on the puff number, NFDPM, nicotine, water or CO yields; in other words, the total production of the smoke and the mechanical filtration by the three types of filter were closely matched. The filter additive particle size was large enough not to influence the pressure drop and thus did not impede the smoke flow during puffing. It is evident from the data that CR20 is an effective adsorbent of smoke aldehydes and HCN.
In summary, reductions in smoke formaldehyde, acetaldehyde and HCN were greater than those that could be achieved using a standard microporous activated carbon operating under a physisorption mechanism.
- Rodgman, A., Perfetti, T. (2008) The chemical components of tobacco and tobacco smoke. CRC Press, Taylor & Francis Group, Boca Raton. 1-928.
- Fowles, J., Dybing, E., (2003). Application of toxicological risk assessment principles to the chemical constituents of cigarette smoke. Tobacco Control. 12: 424-430.
-
Branton, P., McAdam, K., Winter, D., Liu, C., Duke, M., Proctor, C.(2011) Reduction of aldehydes and hydrogen cyanide yields in mainstream cigarette smoke using an amine functionalised ion exchange resin. Chemistry Central 5: 15. Full text: Reduction of aldehydes...
- Horsewell, H., Phelpstead, J. US Patent No. 4,300,577
- Zagorodni, A. (2006) Ion exchange Resins: Properties and Applications, Elsevier, Chpt 1
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