Effect of the Concentration of Siliceous Materials Added to Tobacco

Article pubs.acs.org/IECR

Effect of the Concentration of Siliceous Materials Added to Tobacco Cigarettes on the Composition of the Smoke Generated during Smoking A. Marcilla, M. I. Beltrán,* A. Gómez-Siurana, I. Martínez, and D. Berenguer Dpto. Ingeniería Química, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain S Supporting Information *

ABSTRACT: Two as-synthesized meso- and macro-porous siliceous materials (MPSMs), i.e., Al-MCM-41 and SBA-15, were mixed with tobacco to study their effect on tobacco smoke chemistry. A reference cigarette, 3R4F, and a commercial cigarette, Fortuna, containing different percentages of MPSM were smoked in a smoking machine, and the mainstream smoke was analyzed. SBA-15 showed the highest reductions of nicotine; close to 90% when it was added at 8 mass %. The superb behavior of these materials may be related to their high particulate matter filtering efficiency in combination with their catalytic activity. The selectivity of these materials with respect to nicotine was also analyzed. Al-MCM-41 presents higher selectivity for condensed compounds than for gases, whereas SBA-15 presents similar ratios for both fractions. The highest selectivity was obtained for the liquid fraction when smoking 3R4F cigarettes mixed with Al-MCM-41.

1. INTRODUCTION In 1956, tobacco was declared as the leading cause of foreseeable death by the World Health Organization (WHO),1 and since then the consumption of tobacco has been the main cause of the development of chronic diseases, disabilities, and premature deaths in developed countries. Consequently, most governments have imposed restrictions on tobacco consumption in public places. Nevertheless, these restrictions do not guarantee a decrease in the consumption of tobacco, nor reduce its effect on smokers. The composition of cigarette smoke is complex. Tobacco is a plant material composed of over 4000 compounds. When tobacco is smoked, the alternating cycles of puff−smolder−puff cause large temperature changes at different points of the cigarette. Meanwhile, several processes occur, including pyrolysis, distillation, combustion, pyrosynthesis, condensation, and dilution, all of which may contribute to the formation of the complex mixture that is tobacco smoke.2−6 Two streams of smoke are normally considered, mainstream smoke (MSS) and sidestream smoke (SSS). The first comprises around 25% of the total smoke generated and transverse the length of the cigarette before being directly inhaled by the smoker, whereas SSS is generated by the smoldering end of a cigarette and is partly inhaled by passive smokers. Early studies with the objective of reducing the toxicity of tobacco smoking date back to 1957. In these first studies, cigarettes were modified, either by using different designs or materials for filters, adding extra-ventilation in the filter area, or modifying the paper permeability. With the introduction of ventilated filters, for example, the volume of gas passing through the cigarette decreases, leading to a lower consumption of tobacco during puffs and the consequent smaller yield of compounds generated in the MSS. Other authors also summarize progress made in research on reducing tobacco toxicity.7 These authors describe how different technologies have evolved for making cigarettes “less harmful”. © 2015 American Chemical Society

The use of zeolites and other aluminosilicates as additives to reduce the toxicity of tobacco smoke has been described more recently by several authors. For example, Cvetkovic et al.8 used Cu-ZSM-5 zeolite to reduce the amount of NO and NOx in MSS. This zeolite was added to the cigarette filter or directly mixed with tobacco, and the mechanism proposed was based on the properties of adsorption or diffusivity of the material. Xu et al.9 reported the use of different zeolites and two mesoporous materials (i.e., zeolites NaA, NaY, KA and NaZSM-5, SBA-15 and MCM-48) as cigarette additives capable of reducing the tobacco specific nitrosamine (TSNA) content in the cigarette smoke by selective adsorption. Yong et al.10 described the use of Cerium-containing MCM-48 materials to reduce PAH content in mainstream tobacco smoke. Filters have also been used with carbon nanotubes or activated carbon and NaY zeolite.11 The use of oxide iron particles to remove CO was described by Li and Hajaligol.12 Gao et al.13 employed a zeolite-like calcosilicate in the filter type to reduce the level of harmful TSNA in MSS. Branton et al.14 described the use of activated carbon in the filters to adsorb the constituents of MSS. Their studies are focused on analyzing how the pore structure of the activated carbon affects the adsorption of the compounds generated in the gaseous phase of smoking a cigarette. More recently, Radojicic et al.15 studied the possibility of selective reduction of PAHs in cigarette smoke by applying different amounts of CuZSM-5 zeolite (1 and 3 wt %) directly to the cigarette blend. The total PAH reduction was 40% for 3% of zeolite. Lin et al.16 introduced MCM-41, SBA-15, NaA, NaZSM-5, NaY, and HZSM-5 into cigarette rods mixed with Burley tobacco at 4 wt % to investigate the performance of Received: Revised: Accepted: Published: 1916

October 1, 2014 December 20, 2014 January 26, 2015 January 26, 2015 DOI: 10.1021/ie5038837 Ind. Eng. Chem. Res. 2015, 54, 1916−1929

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Industrial & Engineering Chemistry Research Table 1. Number of Puffs, Actual MPSM Content, Total Amount of Tobacco Smoked, TPM-F, and TPM-T sample

number of puffs

catalyst content (wt %)

amount smoked (g)

TPM-F (mg/g of smoked tobacco)

TPM-T (mg/g of smoked tobacco)

3R4F 3R4F + 4% Al-MCM-41 3R4F + 6% Al-MCM-41 3R4F + 8% Al-MCM-41 3R4F + 4% SBA-15 3R4F + 6% SBA-15 3R4F + 8% SBA-15 Fortuna Fortuna + 4% Al-MCM-41 Fortuna + 6% Al-MCM-41 Fortuna + 8% Al-MCM-41 Fortuna + 4% SBA-15 Fortuna + 6% SBA-15 Fortuna + 8% SBA-15

9.2 9.3 9.7 10.0 9.0 9.0 10.0 8.7 9.0 9.3 9.7 8.7 9.3 11.0

0.0 3.8 5.6 7.3 3.8 5.6 7.3 0.0 3.8 5.7 7.4 3.8 5.6 7.4

8.87 8.36 8.43 8.57 9.42 8.68 8.43 8.27 8.11 8.26 8.19 8.09 9.00 8.41

29.5 23.9 17.2 15.0 9.9 10.3 8.4 17.5 12.5 10.9 8.43 9.82 8.77 7.84

11.4 8.15 5.75 3.85 3.45 2.265 1.18 12.7 9.73 8.07 5.10 5.22 3.08 1.73

2. EXPERIMENTAL SECTION 2.1. Preparation and Characterization of Al-MCM-41 and SBA-15. Two silica materials, Al-MCM-41 and SBA-15, were synthesized. Al-MCM-41 synthesis was reported elsewhere.19 To synthesize SBA-15, triblock poly(ethylene oxide)b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (Sigma-Aldrich) was dissolved in 150 mL of 1.6 M solution of HCl. An 8.4 g sample of tetraethyl orthosilicate (99%, Aldrich) were added to the solution, and the mixture was maintained at 40 °C and was stirred for 20 h. The mixture was then aged at 100 °C for 24 h. The white solid powder was collected by filtration, dried at 100 °C, and calcined at 550 °C for 5 h. MPSMs characterization was as follows. N2 adsorption isotherms at 77 K were measured in an automatic AUTOSORB-6 supplied by Quantachrome. The surface area values were obtained according to the Brunauer−Emmett− Teller (BET) method. Pore size distributions were obtained by applying the Barrett−Joyner−Halenda (BJH) model with cylindrical geometry of the pores and using the de Boer equation to determine the adsorbed layer thickness (t) and the external surface area. Scanning electron microscopy (SEM) photographs were taken with a JEOL JSM-840. The Si/Al content of Al-MCM-41 was measured by X-ray fluorescence (XRF) in a sequential spectrometer of X-rays (Philips Magix Pro), and its acidity was measured by temperature-programmed desorption (TPD) of ammonia, performed in a Netzsch TG 209 thermobalance, following the procedure described elsewhere.21 The apparent density was calculated as the ratio of the mass of loose catalyst that occupies a 40 mL cylinder. 2.2. Cigarette Preparation and Smoking Experiments. Two types of tobacco cigarettes were used; the research reference cigarettes 3R4F from the University of Kentucky (Kentucky Tobacco Research and Development Center) and a commercial tobacco brand, Fortuna, manufactured by the Imperial Tobacco Group. Fortuna cigarettes are an American blend, composed mainly of Virgina tobacco. The 3R4F research reference cigarettes are a mixture of flue cured, Burley, and reconstituted tobacco, and they are commonly employed as a reference because of the relatively high dispersion of the results of smoking experiments. Before the smoking experiments were performed, 200 cigarettes of each type were disassembled and the tobacco, filters, and paper were weighed separately. The tobacco was

these molecular sieves in the in situ removal of some carcinogens in tobacco smoke. They found that SBA-15 could reduce TSNAs in MSS by up to 35%. In all of these studies, the authors assume combined adsorption−catalysis mechanisms to explain their results, although the actual mechanisms explaining the route of each component of the smoke are still unknown. Our previous study17 showed that MCM-41 synthesized by different processes (calcination and extraction of the template) reduced carbon monoxide (CO) and total particulate matter (TPM) in tobacco smoke. Then the effect of the aluminum content on an as-synthesized MCM-41 on the amount of some toxic compounds present in the particulate matter of tobacco smoke was studied.18 Other zeolites (HUSY, HZSM-5, and Hβ) together with Al-MCM-4119 were also used, obtaining for Al-MCM-41 a notable ability to reduce the yields of some known carcinogenic compounds from different families, such as carbonyls, phenolic, and especially nitrogenous compounds (up to 40% reduction). In the above-mentioned papers, meso- and macro-porous siliceous materials (MPSMs) were directly mixed with tobacco at 4 wt %. The WHO20 in the executive summary and recommendations of a technical report recommends “...establishing levels of selected mainstream toxicants per milligram of nicotine”. Thus, it is very important to know the effect of the additives used to reduce the toxicity of tobacco smoke on nicotine and tars. Very few articles report such data or even allow such comparisons because many of them report results only on the toxicants analyzed. The objective of the present paper is to study the effect of the concentration of Al-MCM-41 and SBA-15 added to tobacco on the composition of MSS. The composition of the smoke obtained under International Organization for Standardization (ISO) smoking conditions for a reference research cigarette and for a commercial brand and the mixtures of different percentages of tobacco plus MPSM were analyzed and compared. Thirty-four compounds were identified in the vapor fraction and 57 in the particulate matter. The particulate matter retained in the filters of the cigarettes was also analyzed and compared with the particulate matter retained in the traps. Moreover, and following the recommendations of the WHO,20 the ratio of the reduction of the compounds and families analyzed to nicotine is also reported to study the selectivity of these MPSMs for reducing the toxicity of tobacco smoke. 1917

DOI: 10.1021/ie5038837 Ind. Eng. Chem. Res. 2015, 54, 1916−1929

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Industrial & Engineering Chemistry Research

mesoporous materials (Supporting Information, Figure S1), with an average pore size of around 2.7 nm. However, SBA-15 presents an isotherm characteristic of macroporous materials, showing a similar shape for the isotherm but with the step appearing at around P/P0 0.6−0.8, because of the adsorption of the N2 on the macropores,23 with an average pore size of 6.1 nm. Al-MCM-41 desorbs NH3 in a single step at 171 °C, showing a medium acidity, while SBA-15 is a nonacid catalyst which does not contain aluminum (Table 2). SEM photographs

tumbled, and the amount of tobacco in the original cigarettes was weighed out (0.70 g in the case of 3R4F and 0.80 g in the case of the commercial brand) and mixed manually with the corresponding amount of catalyst, 0.028−0.061 g, depending on the desired percentage. Therefore, the nominal concentration of catalyst in the cigarettes was within the 4−8% (w/w) range. The cigarettes were reassembled using the original papers and filters for each cigarette type. The cigarettes were conditioned for at least 48 h at 22 °C and a relative humidity of 60%. Cigarettes without MPSM were prepared in the same conditions. The cigarettes were smoked in a smoking machine which has been described elsewhere, under ISO Standard 3308 smoking conditions. Fifteen cigarettes were smoked for each experiment. The cigarettes were placed in the ports of the smoking machine ensuring that the ventilation holes were not blocked. Three different fractions were collected from the MSS, as explained elsewhere.22 Global yields of the total particulate matter were obtained by before and after difference weighing of the filters of the cigarettes (TPM-F) and the Cambridge pads employed as traps (TPM-T). The amount of tobacco smoked was calculated as the difference between the initial amount of tobacco contained in the cigarette and the tobacco remaining in the butt after smoking. The noncondensed products were collected in a Tedlar bag located after the Cambridge pads. Table 1 shows the name assigned to the prepared mixtures and the global results obtained in the smoking experiments, including the average number of puffs when smoking up to the butt length indicated in ISO Standard 3308, actual percentage of catalyst and tobacco introduced into the cigarette rod, total amount of tobacco smoked for the 15 cigarettes, and TPM-F and TPM-T. The gas fraction was analyzed immediately by gas chromatography with thermal conductivity detector (GC/ TCD, Shimadzu GC-14A) using CTR I column and flame ionization (GC/FID Agilent GC 6890N) using a capillary GAS-PRO column. Thirty-four compounds were identified in the gaseous fraction. To determine the yields of nicotine and other condensed compounds, both filters and traps were analyzed following the method described in ISO Standard 4387. This standard describes the procedure for the analysis of the particulate matter, nicotine, and water. Other compounds were also identified and quantified in TPM. The analysis of TPM was performed by gas chromatography−mass spectrometry (Agilent HP-6890N GC with MS HP-5973 MSD), using an HP-5MS column and the standards described elsewhere.19 The condensed fraction is a very complex mixture, showing more than 120 observable peaks in the GC/MS chromatograms. In this case, only compounds identified by mass spectrometry are shown (i.e., >80% probability; 57 components). The 57 compounds reported represent around 95% of the total area of the chromatograms. However, it is important to note that despite the relatively low probability of assignment by mass spectrometry of the rest of the components, the same peaks, with the same assignments, appeared in all the chromatograms corresponding to the different mixtures analyzed and they followed trends similar to those of the majority of the compounds.

Table 2. Physical Properties of Al-MCM-41 and SBA-15 property

Al-MCM-41

SBA-15

pore Size (nm) BET area (m2/g) total pore volume (cm3/g) Si/Al ratio acidity (mmol/g) apparent density (g/cm3)

2.73 1007 0.83 119 0.3 0.091

6.09 757 1.06 − − 0.045

of both materials (Supporting Information, Figure S2) show that SBA-15 presents a fiberlike aspect in addition to some pseudospherical particles, whereas Al-MCM-41 shows mostly pseudospherical particles. The apparent density of SBA-15 is much lower than that of Al-MCM-41, which could be very important when considering the degree of dispersion of both materials throughout the tobacco strands. 3.2. Analysis of the Vapor Phase. Table 3 shows the yields obtained for the different compounds analyzed in the gas fraction for the 3R4F cigarettes, Fortuna, and all the mixtures of both tobaccos with the MPSM. Reductions mentioned hereafter were obtained using ri = 100(yi − yic )/yi

where yi is the global yield (filter plus traps in the case of the liquid fraction) obtained for a component (or family of components) when no MPSM was added and yic is the global yield obtained for a component (or family of components) when the MPSM was added. When the two types of cigarettes are compared, it can be observed that the yield of most compounds is very similar. In the cases of CO and CO2, an important effect of the catalyst was observed, this effect being larger in the presence of SBA-15. CO is a well-known poison and, more importantly, it is the most concentrated compound found in tobacco smoke among those included in the Hoffmann list.2,24,25 The yield of CO in the case of 3R4F is reduced by more than 50%, varying from 18.6 to 8.77 mg/g of smoked tobacco when the concentration of SBA-15 was 8%. It should be noted that when the concentration of the MPSM increases, the reduction of the CO and CO2 obtained also increases. In the case of the AlMCM-41, reductions are obtained only for a content higher than 6%. Figure 1a,b shows the yields of Table 3 compounds apart from CO, which are included in the Hoffmann list because of their high toxicity.3,24 In this way the effect of the MPSMs on the behavior of these compounds can be analyzed more clearly. In the case of 3R4F with 4% of Al-MCM-41, reductions are observed in only a few compounds, while most of them slightly increase (Figure 1a). The compounds presenting a higher reduction are benzene and toluene which, in this system with 8% of MPSM, were reduced by 22 and 31%. Also noteworthy is the fact that, for this system (3R4F + Al-MCM-41), the yields

3. RESULTS 3.1. Characterization of SBA-15 and Al-MCM-41. Table 1 shows the physical properties of the MPSM used. The N2 adsorption isotherms of Al-MCM-41 is characteristic of 1918


a

1919

paraffin paraffin olefin other paraffin olefin paraffin other paraffin olefin olefin olefin olefin olefin paraffin other other olefin aromatic olefin paraffin olefin aromatic aldehyde aldehyde aldehyde other aromatic aromatic aldehyde aldehyde

18.60 52.25 0.916 0.374 0.192 0.021 0.169 0.185 0.019 0.048 0.050 0.043 0.008 0.013 0.043 0.030 0.014 0.013 0.011 0.012 0.016 0.198 0.008 0.012 0.115 0.454 0.031 0.027 0.048 0.025 0.008 0.005 0.010

3R4F

4% 18.48 51.23 1.074 0.420 0.234 0.031 0.190 0.214 0.022 0.054 0.056 0.050 0.011 0.014 0.049 0.036 0.017 0.018 0.013 0.015 0.018 0.217 0.008 0.013 0.122 0.528 0.042 0.032 0.027 0.024 0.007 0.007 0.008

6% 14.20 40.13 0.825 0.328 0.185 0.028 0.147 0.171 0.032 0.041 0.047 0.047 0.007 0.010 0.039 0.027 0.012 0.017 0.010 0.012 0.012 0.156 0.006 0.011 0.095 0.467 0.042 0.028 0.026 0.021 0.008 0.007 0.007

8% 14.11 40.23 0.823 0.325 0.197 0.028 0.148 0.173 0.020 0.042 0.045 0.039 0.009 0.012 0.042 0.029 0.013 0.013 0.010 0.011 0.015 0.203 0.007 0.010 0.090 0.424 0.042 0.025 0.019 0.018 0.007 0.010 0.008

All amounts are expressed in milligrams of compound/grams of smoked tobacco.

family

compound

CO CO2 methane ethane ethylene acetilene propane propene iso-butane chloromethane butane 1-butene 1,2-propadiene 1,3-butadiene isobutene cis-2-butene pentane methanethiol hydrogen cyanide 1-pentene furan isoprene hexane 1-hexene benzene acetaldehyde acrolein propionaldehyde acetonitrile toluene 2,5-dimethylfuran crotonaldehyde isobutyraldehyde

3R4F + Al-MCM-41 4% 11.32 32.62 0.665 0.275 0.142 0.016 0.126 0.139 0.012 0.036 0.038 0.032 0.006 0.008 0.034 0.025 0.011 0.012 0.008 0.009 0.011 0.168 0.005 0.009 0.079 0.351 0.031 0.018 0.025 0.016 0.005 0.003 0.011

9.95 31.81 0.694 0.281 0.159 0.023 0.126 0.146 0.025 0.035 0.040 0.033 0.007 0.010 0.033 0.023 0.011 0.012 0.009 0.010 0.010 0.150 0.006 0.008 0.077 0.332 0.038 0.019 0.019 0.017 0.004 0.006 0.013

6%

3R4F + SBA-15 8% 8.77 30.40 0.516 0.219 0.126 0.019 0.105 0.116 0.041 0.027 0.046 0.026 0.005 0.007 0.027 0.019 0.008 0.006 0.007 0.007 0.010 0.128 0.004 0.006 0.048 0.195 0.027 0.014 0.007 0.009 0.003 0.007 0.003

17.6 56.7 1.055 0.446 0.240 0.024 0.208 0.234 0.019 0.053 0.064 0.057 0.010 0.018 0.057 0.043 0.019 0.016 0.013 0.019 0.023 0.390 0.018 0.017 0.144 0.570 0.032 0.045 0.093 0.032 0.016 0.006 0.013

Fortuna

4% 19.5 59.4 1.071 0.426 0.254 0.028 0.197 0.233 0.027 0.057 0.060 0.055 0.012 0.018 0.053 0.039 0.017 0.029 0.013 0.015 0.017 0.351 0.017 0.015 0.155 0.581 0.059 0.054 0.091 0.032 0.008 0.019 0.013

17.1 53.5 0.921 0.369 0.226 0.026 0.169 0.209 0.015 0.048 0.052 0.049 0.010 0.016 0.050 0.036 0.015 0.026 0.012 0.015 0.015 0.343 0.017 0.014 0.132 0.597 0.052 0.038 0.067 0.032 0.013 0.008 0.023

6%

8% 12.5 43.9 0.785 0.319 0.191 0.024 0.141 0.178 0.020 0.041 0.045 0.041 0.008 0.013 0.043 0.029 0.013 0.025 0.012 0.013 0.014 0.305 0.014 0.013 0.110 0.460 0.052 0.036 0.066 0.029 0.009 0.007 0.008

Fortuna + Al-MCM-41

Table 3. Gas Yield for the 3R4F and Fortuna Cigarettes without and with Al-MCM-41 and SBA-15 at 4, 6, and 8 wt %a 4% 11.4 39.8 0.686 0.290 0.167 0.022 0.136 0.161 0.028 0.035 0.043 0.038 0.007 0.012 0.039 0.027 0.011 0.016 0.010 0.011 0.013 0.272 0.012 0.010 0.095 0.330 0.043 0.033 0.041 0.017 0.007 0.006 0.008

9.7 32.4 0.547 0.230 0.129 0.014 0.110 0.128 0.042 0.029 0.036 0.030 0.004 0.009 0.031 0.022 0.010 0.011 0.008 0.009 0.010 0.232 0.011 0.007 0.068 0.290 0.032 0.020 0.027 0.016 0.006 0.005 0.015

6%

Fortuna + SBA-15 8% 9.2 32.6 0.521 0.225 0.143 0.024 0.112 0.137 0.145 0.027 0.047 0.031 0.007 0.012 0.037 0.022 0.009 0.009 0.009 0.010 0.012 0.244 0.010 0.008 0.062 0.282 0.032 0.017 0.019 0.013 0.007 0.010 0.006

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Figure 1. Yield of some compounds of the gaseous fraction included in the Hoffmann’s list for (a) 3R4F and (b) Fortuna.

number of minor compounds, although to a lesser extent than Al-MCM-41; crotonaldehyde, with an increase of 59%, and isobutyraldehyde, with an increase of 16%, are the most marked cases. Among the compounds analyzed in the gas fraction included in the Hoffmann list, acetaldehyde and isoprene are the highest (Figure 1a and Figure 1b), and with the exception of Al-MCM41 at low contents, a clear reduction in the content of these compounds can be observed. For example, the amount of acetaldehyde was reduced by more than 50% in the presence of 8% of SBA-15 (from 0.454 to 0.195 mg/g of smoked tobacco for 3R4F, and from 0.580 to 0.282 mg/g of smoked tobacco for Fortuna tobacco). A special mention has to be made of isobutane, which increases, especially with SBA-15 (Table 3). The different compounds have been grouped by chemical families to facilitate the analysis and to evaluate the possible selectivity of the MPSMs.19 In the gas fraction, the following groups have been chosen: paraffin, olefin, aldehyde, aromatic,

of acrolein and crotonaldehyde increase markedly, even doubling the amount obtained without catalyst. When the catalyst employed was SBA-15, larger reductions in almost all compounds were observed. Thus, in the case of 3R4F with 8% of SBA-15, benzene and toluene were reduced by 58 and 64%, respectively. When the tobacco smoked was Fortuna, higher reductions were obtained in the presence of both MPSMs, despite the yield of some compounds increasing at low contents of AlMCM-41 (Figure 1b). In this case, 1,3-butadiene and benzene were the two main compounds reduced (27 and 23%, respectively, at 8% of Al-MCM-41). Nevertheless, the yields of acrolein and crotonaldehyde increase markedly at low concentrations of MPSM (4%). However, SBA-15 behaves much better with practically all compounds, especially in the cases of benzene, propionaldehyde, and toluene. Reductions at 8% of SBA-15 for these compounds were 56, 62, and 58%, respectively. SBA-15 causes an increase in the yield of a small 1920


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Figure 2. Reductions obtained in the different families of compounds considered in the gas fraction: (a) 3R4F tobacco and (b) Fortuna tobacco.

and others (Table 3). Figure 2 shows the reductions obtained for the different families with both types of cigarettes and MPSM. It can be seen, once more, that the greatest reductions were obtained in all families when using the larger concentration of SBA-15 and that larger reductions were obtained with Fortuna. For both cigarettes, the families of aromatic and others are reduced more than the rest, and in the case of the Fortuna cigarettes, the behavior of all families is quite similar. The family “others” includes some important compounds, such as hydrogen cyanide, acetylene, or acetonitrile, and is also reduced. Summarizing, it can be concluded that SBA-15 is more effective in reducing the total amount of gases and especially carbon monoxide. The yields of the individual compounds show a general decreasing trend with increasing catalyst concentration, although a few compounds present the opposite behavior. When the families of compounds are considered, SBA-15 yields significant reductions for all families at all concentrations for both tobaccos, whereas Al-MCM-41 at low concentrations produces the contrary effect of increasing the yields of the different families, especially in the case of 3R4F. Both catalysts are more effective with Fortuna. Finally, aromatics, aldehydes, and others seem to be selectively reduced

with respect to the rest of the families of compounds considered. 3.3. Analysis of the Particulate Matter. If the smoking conditions of ISO Standard 3308 were representative of the behavior of smokers, the particulate matter retained in the traps (TPM-T) would be the fraction that smokers would inhale. The part retained in the filters (TPM-F) does not pass into the smoker, and it is not frequently analyzed. Nevertheless, to properly evaluate the MPSM action, it has been reported in this study. In Table 1, the amount of condensed products in the filters and traps is shown for both types of cigarettes. Globally, the total amount of condensed products (filters plus traps) in 3R4F is higher than that in Fortuna cigarettes. Nevertheless, the amount of condensed products obtained in the traps is quite similar for both types of cigarettes, being slightly greater in the case of Fortuna. This may be due to the fact that the filters of 3R4F are larger than those of Fortuna. Both cigarettes contain cellulose acetate filter tips, but the length of filters in 3R4F cigarettes is 27 mm while that of Fortuna cigarettes is 21 mm, which clearly contributes to a higher filtering efficiency. When TPM-F and TPM-T values when catalysts were added are compared, both catalysts significantly reduce the amount of condensed products, with the effect of SBA-15 being larger than 1921


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Figure 3. Reduction obtained in TPM-F, TPM-T, and TPM-total as a function of the MPSM content for (a) 3R4F cigarettes and (b) Fortuna cigarettes.

without catalyst. Total nicotine (filters and traps) obtained in the case of the 3R4F cigarettes was 2.532 mg/g of smoked tobacco followed by neophytadiene (0.207 mg/g of smoked tobacco), but other compounds are also obtained in a significant proportion, such as phenol (0.079 mg/g of smoked tobacco), furfural (0.068 mg/g of smoked tobacco), hydroquinone (0.064 mg/g of smoked tobacco), and p-cresol (0.058 mg/g of smoked tobacco). A similar tendency can be seen in the case of Fortuna tobacco, in which nicotine (2.485 mg/g of smoked tobacco) is the most abundant compound, but other compounds like neophytadiene (0.148 mg/g of smoked tobacco), furfural (0.086 mg/g of smoked tobacco), phenol (0.078 mg/g of smoked tobacco), p-cresol (0.068 mg/g of smoked tobacco) and hydroquinone (0.056 mg/g of smoked tobacco) are also present in a significant proportion. In general, the smoke generated by both types of cigarettes is very similar, but when 3R4F and Fortuna are compared, the amounts of

that of Al-MCM-41. Figure 3 shows the reduction of TPM obtained in filters, traps, and the total (filters and traps) for 3R4F (Figure 3a) and Fortuna (Figure 3b) as a function of MPSM concentration. The behavior of both MPSMs is somewhat different. These differences are larger at low contents, where SBA-15 presents an activity 2−3 times higher than that of Al-MCM-41, depending on the type of cigarettes analyzed. Whereas SBA-15 is much more efficient at low concentrations, Al-MCM-41 has a larger increase in effectiveness with concentration. Most of the compounds in the condensed fraction are generated at very low concentrations, and the only compound generated in a larger amount, apart from water, is nicotine, which represents more than 80% of the total condensed products shown. Details on the compounds identified in the filters and traps are provided in the Supporting Information (Tables S1 and S2), for the two types of cigarettes, with and 1922


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constitutes the smoke that reaches the traps (or the eventual smoker). The relative amount of nicotine retained in the filters may depend on numerous variables, such as the smoking regime,26,27 aspiration rate (time of contact between TPM and the filters), nature of the filters, and amount of nicotine contained in the smoke. When the catalyst is introduced, the total amount of nicotine in the smoke is reduced, allowing the filters to retain a relatively higher amount of nicotine. As can be seen in Figure 4, for both types of cigarettes and contents of catalyst, nicotine is more efficiently retained by the filters as the total amount of nicotine is reduced. Figure 5 shows the comparison of the yields of some compounds analyzed in TPM-F and TPM-T obtained for 3R4F and Fortuna cigarettes in the absence of MPSM. These compounds have been chosen for several reasons. Some of them are included in the Hoffmann list, while others have been chosen because they are considered to be hazardous materials or as representatives of families of compounds. In general, the tendency observed is that the most volatile compounds (which are also the most polar) are preferentially retained by the filters, whereas these compounds are almost not observed in the traps. This is the case of, for example, furfural, styrene, benzaldehyde, phenol, or 1H-indol. The heaviest compounds are more uniformly delivered between filters and traps, as is the case of nicotine as commented above, or myosmine, 1,4 dihydrophenanthrene, cotinine, or triacontante, shown in Figure 5. This differential filtering behavior depending on molecular weight and the nature of the compounds was described previously, and the explanation may involve different aspects such as the affinity of a particular compound to the filters and traps and their relative concentration and vapor pressure, among others.19,23,25 In the case of Fortuna cigarettes, a few compounds are more abundant in the traps than in the filters, but the most notable is the case of hydroquinone (one of the better-known carcinogens of tobacco smoke), which in filters yielded 0.022 mg/g of smoked tobacco, while in traps 0.034 mg/g of smoked tobacco. This peculiarity can be observed in 3R4F tobacco for only one compound, 1,4-dihydrophenanthrene, where the mass condensed increases from 0.007 in filters to 0.017 mg/g of smoked tobacco in traps. Panels a and b of Figure 6 show the yields of the selected compounds obtained in the traps for 3R4F and Fortuna

compounds condensed in Fortuna traps are greater than those in 3R4F traps (Table 2 and Tables S1 and S2 in the Supporting Information). As mentioned above, the Fortuna filters are smaller than 3R4F filters, so their capacity to retain the different compounds is lower. Figure 4 shows the amount of nicotine condensed in the filter and the trap for all the smoking experiments. As expected,

Figure 4. Nicotine retained in filters and traps for the two types of cigarettes without and with different contents of the two MPSMs.

a higher proportion of nicotine is retained in the filters for 3R4F than for Fortuna cigarettes. Both catalysts are able to significantly reduce the yield of nicotine. For example, in 3R4F cigarettes, nicotine in traps (that which would be inhaled by the smoker) is reduced from 1.099 to 0.470 mg/g of smoked tobacco with 8% of Al-MCM-41 (57% reduction), and to 0.109 with 8% of SBA-15 (90% reduction). The effect in Fortuna is quite similar; nicotine condensed in the traps is reduced from 1.362 to 0.618 mg/g of smoked tobacco (55% reduction) with 8% of Al-MCM-41 and to 0.184 mg/g of smoked tobacco with 8% of SBA-15 (85% reduction). Another important fact to highlight when these MPSMs are introduced is that the distribution of nicotine between filters and traps changes, enhancing the efficiency of the filters. When smoke passes through the filters, some of the nicotine is retained and the rest remains in the particulate matter that

Figure 5. Yield of some compounds analyzed in TPM-F and TPM-T in 3R4F and Fortuna cigarettes. 1923


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Figure 6. Yield of some compounds analyzed in TPM-T with and without MPSM for (a) 3R4F cigarettes and (b) Fortuna cigarettes.

group “others”. The group “others” includes 2-ethyl-tiophene and farnesol. The most important family by far is that of nitrogenous compounds (2.731 mg/g of smoked tobacco in filters plus traps of 3R4F and 2.664 mg/g of smoked tobacco in Fortuna), followed by aliphatics (0.430 mg/g of smoked tobacco), phenolics (0.408 mg/g of smoked tobacco), and carbonyls (0.357 mg/g of smoked tobacco) in 3R4F and carbonyls (0.383 mg/g of smoked tobacco), phenolic (0.375 mg/g of smoked tobacco), and aliphatic (0.300 mg/g of smoked tobacco) in Fortuna cigarettes. The other three families considered (epoxies, aromatics, and others) are less prevalent, around 0.100 mg/g of smoked tobacco in both types of cigarettes. When the MPSMs are introduced, interesting effects are observed. Figure 7 shows the total reduction attained in the different families considered when the MPSMs were added. As seen in Figure 7, the reductions increase almost linearly with MPSM content, for both cigarettes and all families, except for aromatics when using SBA-15. The family of aromatics shows a reduction very close to 90% for both cigarettes with SBA-15,

cigarettes, respectively. As can be seen, the presence of MPSM significantly reduces the formation of the different compounds present in the particulate matter, especially in the case of SBA15, which reduces many compounds to below their detectable limits. To facilitate the comparison of the effect of the MPSM, the compounds analyzed (Tables S1 and S2 in the Supporting Information) have been grouped by families, according to their chemical functionality. The families considered in TPM are the following: nitrogenous, carbonyl, phenolic, epoxy, aromatic, aliphatic, and others. The family “nitrogenous” is mainly composed of pyridine derivatives and some pyrazine, amines, and pyrrols. “Carbonyls” are mainly composed of furfural derivatives and other aldehydes and ketones. The “phenolic” group includes phenol and substituted phenols. The “epoxy” group is mainly composed of furan derivatives and other cyclic or linear epoxy. Among “aliphatic” there is a series of linear or branched alkanes and alkenes from tetradecane to longer chains. Styrene and 1,4-dihydrophenanthrene are included in the “aromatics”. Alcohols not included as epoxy appear in the 1924


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Figure 7. Reduction of the total yields (filter and trap) of the families of compounds considered for all the systems of tobacco and tobacco+MPSM studied: (a) 3R4F cigarettes and (b) Fortuna cigarettes.

4. DISCUSSION The recent recommendation for future regulations proposed by the WHO Study Group20 is to express the toxicant levels per milligram of nicotine. Accordingly, reductions should be selective for the more toxic compounds while maintaining the nicotine level. This idea is based on the compensation mechanism of smokers, through which they would change their smoking habits to obtain the same amount of nicotine as nicotine is reduced. In this case, selective catalysts would be more appropriate to reduce tobacco toxicity. To evaluate such an effect it is necessary to calculate the ratio of the reductions obtained for every compound to that of nicotine. Thus, the ratio to nicotine was obtained as ri/rnicotine. These ratios for the families of compounds considered are shown in Figures 8 (gas fraction) and 9 (TPM). The trends discussed earlier are evident in these new plots, but another feature reflecting the action of the MPSM on the two tobaccos is now more apparent. The values of ri/rnicotine higher than 1 reflect selective reduction of compound i with respect to nicotine. It can be observed that ri/

independent of the MPSM content. In the case of Al-MCM-41, aromatics show reductions much higher than those of the other families. In addition, SBA-15 produces reductions in nitrogenous and others that are lower than those in the rest of families in the case of 3R4F tobacco (Figure 7a), whereas in the case of Fortuna all families behave similarly (Figure 7b). In the case of Al-MCM-41, aromatics and phenolics are reduced to a larger extent than nitrogenous, whereas others are less reduced in the case of 3R4F (Figure 7a). In the case of this MPSM with Fortuna, aromatics, phenolics, and others are less reduced than the rest of the families. When the effects on the different fractions collected are compared, it can be concluded that the MPSMs are more effective in reducing nicotine and particulate matter than CO and gases. 1925


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Figure 8. Selectivity of Al-MCM-41 and SBA-15 for the different families of compounds in the gas fraction when smoking (a) 3R4F and (b) Fortuna cigarettes.

the presence of cations (for example Cu cations,8 cerium,10 or FeO nanoparticles),27,28 adsorption and filtering,13 molecular sieve character of the catalyst, 10 morphology of the particles,13,16 diffusivity of the molecules on the catalysts, activation of the catalyst particles in the hot zone of the tip, coke deposition on the catalysts,21 or the effect on the temperature.29 Nevertheless, the problem of elucidating an actual mechanism to explain the fate of a given compound in an environment as complex as that present in a smoking cigarette, under the temperature and reagent concentrations in unsteady conditions, remains unresolved. Attempts to acquire more insight by using simplified systems have been made, but the results do not exactly correlate with those obtained under more realistic conditions. Fortunately, the system responds to the general well-established principles of catalysis, and some general correlations can be obtained. Nevertheless, other aspects remain unexplained. The experimental observation that SBA-15 presents better results than Al-MCM-41 must be related to the larger pore size of this material in addition to its lower apparent density, which may contribute to a better dispersion on the tobacco strands. Both MPSMs present a linear increase of their activity with their concentration, but whereas Al-MCM-41 presents the expected tendency of the line passing through the origin, SBA-15 seems to present a positive y-axis intercept, thus showing higher activities at low

rnicotine of most families, both in gases and TPM, decreases with the MPSM concentration (except for gases and Al-MCM-41). On the other hand, Al-MCM-41 seems to be more effective in TPM than in gases and produces greater reductions with respect to nicotine at the lowest concentrations. SBA-15 seems to show similar behavior with gases and liquids and also exhibits the best selectivity at the lowest concentrations. The case of AlMCM-41 with 3R4F is noteworthy in TPM, where all the families, except “others”, and mainly the phenolics, present ratios much higher than 1 (reaching almost 9 for phenolics when using 4% of MPSM). The individual compounds, both in gases and liquids, follow similar trends. Most of them decrease their ratios with increased amounts of MPSM although a few present the opposite trend. These results, in addition to the presence of coke deposited on the catalysts as reported elsewhere,17 clearly show that MPSMs, in addition to their adsorbent role, have a catalyst function in the sense of modifying certain reaction pathways. The knowledge of the described behavior may be very important if these solids are eventually used as tobacco smoke toxicity modifiers. Several studies have been found in the literature in which different materials have been used as catalysts for reducing smoke toxicity. In some cases, mechanistic considerations have been used to explain the results presented. Different aspects have been considered to explain the behavior observed, such as 1926


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Figure 9. Selectivity of Al-MCM-41 and SBA-15 for the different families of compounds in the liquid fraction when smoking (a) 3R4F and (b) Fortuna cigarettes.

mechanism. The selectivity to aromatics of Al-MCM-41 despite the low yield of these compounds, or the relatively low reduction attained by the nonpolar aliphatic compounds, despite their relatively high yield, and the selectivity to Aromatics of SBA-15 or the decrease of all the families in gases, prove this. These aspects may explain the larger effect of both MPSMs on TPM than on the gases fraction. The different reductions observed in the different families remain very difficult to explain, and other types of experiments should be carried out to clarify these points.

concentrations. To explain this trend, the low apparent density of SBA-15 may be very important because it may allow an almost complete coverage of the tobacco strands even at low concentrations, justifying the saturating effect of SBA-15 at lower concentrations as compared to Al-MCM-41. Compounds in the TPM and in the gas phase formed during tobacco pyrolysis and combustion would collide with the MPSM spread over the tobacco threads. A part of TPM would remain on the MPSM, while the rest would travel with the gas to the filters. The catalyst particles which are closer to the burning area (temperatures up to 1000 °C) may collapse, and the structure may be partially or totally destroyed. This MPSM becomes part of the ash together with the compounds retained on it. However, during smoldering, the temperature (below 600°)2,29 is not too high to damage the MPSM structure (see TG of MPSMs in Figure S3 in Supporting Information). As the hot zone approaches the MPSM, the compounds retained on it would, in part, evaporate and condense again on the MPSM− tobacco threads found thereafter, or it would remain on the partially destroyed MPSM located in the combustion area and become part of the ash. In a previous work15,17 it was shown that the amount of ash increases in cigarettes where catalysts were added. On the other hand, some catalytic effect also accompanies this filtering

5. CONCLUSIONS In this study an important reduction in the amount of most compounds of tobacco smoke was demonstrated when AlMCM-41 and SBA-15 were directly mixed with tobacco. Greater activity was found with SBA-15, which even at the lowest contents studied significantly reduced most of the compounds analyzed. With Al-MCM-41, a major dependence on the catalyst concentration was found. For example, the addition of SBA-15 to 3R4F cigarettes at 4, 6, and 8% reduced CO by 39, 47, and 53%, respectively. The same amounts of AlMCM-41 reduce CO by 1, 22, and 23%. Nicotine retained in the traps is reduced by 65, 77, and 90% with the above SBA-15 content, while with Al-MCM-41 the reductions are 4, 34, and 1927


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(6) Czégény, Z.; Blazsó, M.; Várhegyi, G.; Jakab, E.; Liu, C.; Nappi, L. Formation of selected toxicants from tobacco under different pyrolysis. J. Anal. Appl. Pyrolysis 2009, 85, 47−53. (7) Green, C. R.; Schumacher, J. N.; Rodgman, A. The expansion of tobacco and its effect on cigarette mainstream smoke properties. Beitr. Tabakforsch. Int. 2007, 22, 317−345. (8) Cvetkovic, N.; Adnadjevich, B.; Nikolic, M. Catalytic reduction of NO and NOx content in tobacco smoke. Beitr. Tabakforsch. Int. 2002, 2, 43−48. (9) Xu, Y.; Zhu, J. H.; Ma, L. L.; Ji, A.; Wei, Y. L.; Shang, X. Y. Removing nitrosamines from mainstream smoke of cigarettes by zeolites. Microporous Mesoporous Mater. 2003, 60, 125−138. (10) Yong, G.; Jin, Z.; Tong, H.; Yan, X.; Li, G.; Liu, S. Selective reduction of bulky polycyclic aromatic hydrocarbons from mainstream smoke of cigarettes by mesoporous materials. Microporous Mesoporous Mater. 2006, 91, 238−243. (11) Chen, Z.; Zhang, L.; Tang, Y.; Jia, Z. Adsorption of nicotine and tar from the mainstream smoke of cigarettes by oxidized carbon nanotubes. Appl. Surf. Sci. 2006, 252, 2933−2937. (12) Li, P.; Hajaligol, M. Oxidant/catalyst nanoparticles to reduce carbon monoxide in the mainstream smoke of a cigarette, US Patent Application 20030075193 A1, 2003. (13) Gao, L.; Cao, Y.; Zhou, S. L.; Zhuang, T. T.; Wang, Y.; Zhu, J. H. Eliminating carcinogenic pollutants in environment: Reducing the tobacco specific nitrosamines level of smoke by zeolite-like calcosilicate. J. Hazard. Mater. 2009, 169, 1034−1039. (14) Branton, P.; Lu, A.; Schüth, F. The effect of carbon pore structure on the adsorption of cigarette smoke vapour phase compounds. Carbon 2009, 47, 1005−1011. (15) Radojicic, V.; Alagic, S.; Adnadjevic, B.; Maktouf, A. M. Effect of varied quantities of zeolite on the reduction of polycyclic aromatic hydrocarbons in tobacco smoke. Afr. J. Biotechnol. 2012, 11, 10041− 10048. (16) Lin, W. G.; Zhou, Y.; Cao, Y.; Zhou, S. L.; Wan, M. M.; Wang, Y.; Zhu, J. H. Applying heterogeneous catalysis to health care: In situ elimination of tobacco-specific nitrosamines (TSNAs) in smoke by molecular sieves. Catal. Today 2013, 212, 52−61. (17) Marcilla, A.; Beltrán, M.; Gómez-Siurana, A.; Martínez, I.; Berenguer, D. Template removal in MCM-41 type materials by solvent extraction. Chem. Eng. Res. Des. 2011, 89, 2330−2343. (18) Marcilla, A.; Beltrán, M.; Gómez-Siurana, A.; Martínez, I.; Berenguer, D. Catalytic Effect of MCM-41 in the Pyrolysis and Combustion Processes of Tobacco. Effect of the Aluminum Content. Thermochim. Acta 2011, 518, 47−52. (19) Marcilla, A.; Gómez-Siurana, A.; Martínez-Castellanos, I.; Berenguer, D.; Beltrán, M. I. Reduction of tobacco smoke components yields by zeolites and synthesized Al-MCM-41. Microporous Mesoporous Mater. 2012, 161, 14−24. (20) WHO Technical Report Series 951, The Scientifc Basis of Tobacco Product Regulation; WHO Press, World Health Organization: Geneva, Switzerland, 2008. (21) Marcilla, A.; Gómez-Siurana, A.; Berenguer, D. Study of the influence of the characteristics of different acid solids in the catalytic pyrolysis of different polymers. Appl. Catal., A 2006, 301 (2), 222− 231. (22) Marcilla, A.; Martínez, I.; Berenguer, D.; Gómez-Siurana, A.; Beltrán, M. I. Comparative study of the main characteristics and composition of the mainstream smoke of ten cigarette brands sold in Spain. Food Chem. Toxicol. 2012, 50, 1317−1333. (23) Rouquerol, J.; Avnir, D.; Fairbridge, C. W.; Everett, D. H.; Haynes, J. M.; Pernicone, N.; Ramsay, J. D. F.; Sing, K. S. W.; Unger, K. K. Recommendations for the characterization of porous solids. Pure Appl. Chem. 1994, 66, 1739−1758. (24) Hoffmann, A. D.; Hoffmann, I. The changing cigarette, 1950− 1995. J. Toxicol. Environ. Health 1997, 50, 307−364. (25) Fowles, J.; Dybing, E. Application of toxicological risk assessment principles to the chemical constituents of cigarette smoke. Tobacco Control 2003, 12, 424−430.

57%, respectively. The research reference cigarette and the commercial brand behave very similarly, and there were no noteworthy differences in the effect of the catalysts. The effect of SBA-15 and Al-MCMC-41 is higher on the particulate matter. The highest efficiency of SBA-15 over AlMCM-41, especially in particulate matter reduction, is attributed to its fiberlike morphology, lower apparent density, and larger pore size, which would help in mixing the catalyst with the tobacco, and in the interactions with the particulate matter contained in the tobacco smoke as it passes through the cigarette rod. Both catalysts, especially Al-MCM-41, present higher selectivity with regard to nicotine at the lowest catalysts concentrations and are more effective in the liquid fraction than in the gas fraction. Knowledge of the toxicity reduction ability of these catalysts as well as of their selectivity behavior may be very important if these solids are to be used as eventual tobacco smoke toxicity modifiers.

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ASSOCIATED CONTENT

S Supporting Information *

N2 adsorption isotherms at 77 K (Figure S1); SEM photographs of Al-MCM-41 and SBA-15 (Figure S2); thermogravimetric analysis of SBA-15 and Al-MCM-41 up to 750 °C in nitrogen atmosphere and 10 °C/min (Figure S3); compounds identified in the fraction condensed in the filters of the 3R4F and Fortuna cigarettes with Al-MCM-41 and SBA-15 at 4, 6, and 8% (Table S1); and compounds identified in the fraction condensed in the filters of the 3R4F and Fortuna cigarettes with Al-MCM-41 and SBA-15 at 4, 6, and 8% (Table S2). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +34 96 590 2526. Fax: +34 96 590 3826. E-mail: maribel. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support for this research was provided by the Spanish ́ “Comisión de Investigación Cientifica y Tecnológica” of the “Ministerio de Ciencia e Innovación”, the European Community (FEDER refunds) (CTQ2008-01023/PPQ and MAT201124991), and PROMETEO/2012/015.

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REFERENCES

(1) World Health Organization. WHO Framework Convention on Tobacco Control; WHO Document Production Services: Geneva, Switzerland, 2003. (2) Li, B.; Pang, H. R.; Zhao, L. C.; Wang, B.; Liu, C.; McAdam, K. G.; Luo, D. S. Quantifying gas-phase temperature inside a burning cigarette. Ind. Eng. Chem. Res. 2014, 53, 7810−7820. (3) Baker, R. R.; Bishop, L. J. The pyrolysis of non-volatile tobacco ingredients using a system that simulates cigarette combustion conditions. J. Anal. Appl. Pyrolysis 2005, 74, 145−170. (4) Borgerding, M.; Klus, H. Analysis of complex mixtures − Cigarette smoke. Exp. Toxicol. Pathol. 2005, 57, 43−73. (5) Senneca, O.; Ciaravolo, S.; Nunziata, A. Composition of the gaseous products of pyrolysis of tobacco under inert and oxidative conditions. J. Anal. Appl. Pyrolysis 2007, 79, 234−243. 1928


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Industrial & Engineering Chemistry Research (26) Counts, M. E.; Morton, M. J.; Laffon, S. W.; Cox, R. H.; Lipowicz, P. J. Smoke composition and predicting relationships for international commercial cigarettes smoked with three machinesmoking conditions. Regul. Toxicol. Pharmacol. 2005, 41, 185−227. (27) Purkis, S. W.; Mueler, C.; Intorp, M.; Seidel, H. The influence of cigarette designs and smoking regimes on vapour phase yields. Beitr. Tabakforsch. Int. 2010, 24, 33−44. (28) Li, P.; Rasouli, F.; Hajaligol, M. R. Application of nanoparticle iron oxide in cigarette for simultaneous CO and NO removal in the mainstream smoke. Beitr. Tabakforsch. Int. 2004, 21, 1−8. (29) Radojicic, V.; Nikolic, M.; Adnadjevic, B. G. The influence of zeolite type added to cigarette blend on the changes of pyrolytic temperatures. Hem. Ind. 2009, 63, 579.

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Effect of the Concentration of Siliceous Materials Added to Tobacco

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