Capturing nitrosamines in cigarette smoke by zeolite
Zeolite is a group of porous aluminosilicates with regular nano-sized pores. It has the ability to recognize and discriminate molecules with precision of less than 0.1 nm, thus offering potentials for selective adsorption. By carefully selecting its properties, we found strong interactions between some zeolites and nitrosamines present in cigarette smoke. The objective of this study was to compare the efficiency of different zeolites in adsorbing nitrosamines under both laboratory and cigarette smoking conditions. For zeolites to be used in cigarette filters, instantaneous adsorption and desorption of volatile nitrosamines in gas stream was studied by varying temperature, contact time, pore structure, surface acidity-basicity of zeolite and the constitution of the adsorbates. The results showed that both NaY and HZSM-5 zeolites trapped 80% of nitrosamines in the mainstream smoke. However, one third of the trapped nitrosamines desorbed from NaY whereas one-tenth from HZSM-5 upon heating to 773 K. For zeolites to be added onto tobacco blends, we sprayed the two zeolites onto a Chinese Virginia cut tobacco at 3 wt% and made filter-tipped cigarettes. The smoke results showed that nitrosamines in the sidestream and mainstream smoke were reduced by 40-60% and 50-70% respectively. For TSNA, the reduction was 25-32% and 35-60%, respectively. These reductions were achieved without significantly altering the tar and nicotine levels of the cigarettes. In conclusion, it is feasible to use zeolites in cigarettes to reduce the nitrosamine level of cigarette smoke.