The Effects of Cigarette Filter Ventilation on Delivery and Retention of Organic Acids

Cigarette samples with cellulose acetate (CA) filters were prepared for testing in the experiments. The design specifications are shown in Table 1.

The cigarette samples were smoked on a Cerulean SM450 (Cerulean, Milton Keynes, UK) smoking machine according to the ISO (35 mL puff volume, 2 s puff duration, 1 puff/min) and HCI (55 mL puff volume, 2 s puff duration, 1 puff/30 s) standard conditions. In order to trap organic acids in the gas phase of the mainstream cigarette smoke, one impinger, containing dichloromethane (20 mL) and trans-2-hexenoic acid (50 μg/mL) as an internal standard (IS), was connected to the Cambridge filter pad holder. TPM from 5 cigarettes under ISO smoking or 2 cigarettes under HCI smoking was collected on 44-mm Cambridge pads. The content of organic acids in the gas phase and in TPM were determined respectively.

After smoking was completed, an aliquot (1 mL) of the smoke vapour collected in the impinger solution was transferred to the chromatogram vial, and bis(trimethylsilyl)trifluoroacetamide (BSTFA) (60 μL) was added. After reaction for 50 min in a water bath at 60 °C, the vial was taken out, cooled to room temperature and then analyzed by GC-MS directly. The Cambridge pad which collected the smoke particulate phase was transferred to the sample bottle, and dichloromethane (6 mL) was added containing 50 μg/mL IS. The samples were ultrasonically extracted at room temperature for 20 min, and supernatant (1 mL) was taken which was filtered with microporous membrane (0.45 μm) then transferred into the chromatogram vial with addition of BSTFA (60 μL) and reacted for 50 min in a water bath at 60 °C. Finally, the vial was taken out and cooled to room temperature then analyzed as before. Each cigarette sample was smoked and analysed in 3 repetitions, and the results were presented as 3 replicates.

GC-MS (Agilent 7890) conditions:

60 m × 0.25 mm i.d. × 0.25 μm;

This was kept for 3 min, then heated 4 °C/min to 280 °C and maintained for 40 min.

transmission line temperature: 28 °C;

Monitoring modes, full scan mode and selected ion scan mode was used. The retention time and monitor ions of 30 organic acids are shown in Table 2.

According to the corresponding smoking regimes the mainstream cigarette smoke yields of TPM, nicotine, NFDPM, carbon monoxide and water were determined after smoking cigarettes on a Cerulean SM450 smoking machine.

The methods for analyzing the retention and distribution patterns of organic acids in the filter were similar to those previously reported (23). A schematic illustration and the parameters of how the filters were cut are shown in Figure 1.

Figure 1

Since the CA filter contains a small amount of residual acetic acid, it needed to be run as a blank and deducted when determining the amount of organic acid retention in the filter. The calibrated organic acid concentrations in different filter segments were processed by interpolation and polynomial fitting, and filter retention distributions of organic acids were obtained.

A series of standard mixture solutions of 30 organic acids were prepared. After these samples were derivatized with BSTFA, they were analyzed by GC-MS. The results showed that the linear correlation coefficients of all 30 organic acids were in the range of 0.9990–0.9999 (Table 2).

The chromatograms in selected ion monitoring (SIM) mode of the organic acids standard mixture solution are shown in Figure 2. An aliquot (1 mL) was taken of the lowest concentration organic acid standard solution for derivatization across 10 replicates to determine the standard deviation (SD). The limit of detection (LOD) and limit of quantification (LOQ) of the method was equal to 3 times SD and 10 times SD, respectively, and correspondingly the content of organic acids in cigarette smoke could be calculated. A known amount of organic acids standard mixture solution was added to the TPM samples, and the treatment process and quantitative analysis were performed in parallel and repeated 6 times.

Figure 2

The recovery was calculated based on the measurement results. The results in Table 2 show that the recovery of all acids was above 80% except for formic and acetic acids. This might result from the partial volatilization of formic acid and acetic acid during the treatment process. For establishing the relative standard deviations (RSDs), the same cigarette sample was tested 6 times under the same conditions. The results in Table 2 show that the RSDs of the 30 organic acids are all less than 8.6%, indicating that such a method has good repeatability and is suitable for the quantitative analysis of organic acids in cigarette smoke.

Table 3 shows the gas phase yields of organic acids at different filter ventilation levels under ISO and HCI smoking regimes. Only two organic acids were detected in the gas phase of mainstream cigarette smoke (i.e., formic acid and acetic acid). Compared with their yields in particulate phase, they accounted for only a small proportion (5%) of the total. By increasing ventilation of the filter, their yields gradually decreased. When the filter ventilation was 40%, the drop of formic acid was 23%, and the drop of acetic acid was 24%. Comparing with ISO smoking regime (0% ventilation), under HCI smoking regime (ventilation blocked), the yield of formic acid was increased by 47%, and the yield of acetic acid was increased by 44%.

Table 4 lists the yields and reduction ratios of the organic acids in cigarette smoke at five different filter ventilation levels under the ISO smoking regime, and with blocked-ventilation under HCI smoking regime.

It was found that the yields of formic acid, acetic acid, lactic acid, palmitic acid, linoleic acid and linolenic acid were all higher than 49 μg/cig, and the other organic acids were lower than 25 μg/cig when the filter was not ventilated. However, when the yield of carboxyl substances was calculated, the yields of formic acid, acetic acid and lactic acid were 1.07, 2.03, 0.78 mol/cig, respectively, and the other organic acids were lower than 0.35 mol/cig. Since the other organic acids have longer carbon chains and weaker acidity, these organic acids with larger amounts of carboxyl substances have a greater influence on the acid-base equilibrium of the cigarette smoke. When the filter ventilation was increased, the yields of all organic acids decreased, but in different proportions. The organic acids with lower BP and lower MW were more affected by the increase of ventilation, e.g., when the ventilation was 40%, the reduction ratio of formic acid was 58% and the reduction ratio of acetic acid was 57%. The organic acids with higher BP and higher MW were less affected by the increase of ventilation, e.g., BP of oleic acid and stearic acid were 360 °C and 361 °C, and the MWs were 282 amu (atomic mass unit) and 284 amu, respectively, which were relatively higher than those of the other organic acids. The reduction ratios for these two organic acids were 19% and 19% at 40% ventilation, which is lower than that of the other organic acids. These results are similar to those previously reported (20–21). Compared with the ISO smoking regime, the puff volume of the HCI smoking regime is increased, puff interval is shortened, and the yields of organic acids is increased, but the extent of increase of different organic acids is different. The yield of formic acid was increased by 117%, and the yield of palmitic acid was only increased by 10%. In the HCI smoking regime the ventilation holes were blocked, thus no conclusions regarding the effect of filter ventilation on the yields of organic acids could be made.

The yields of routine smoke components at different filter ventilation levels under the ISO smoking regime and a comparison of the yields between ISO and HCI smoking regimes are shown in Table 5.

With increasing filter ventilation, the yields of routine smoke components were all reduced. The reduction ratios of NFDPM and TPM are similar to the filter ventilation levels. The BP (247 °C) and MW (162 amu) of nicotine are obviously higher than those of water. When the filter ventilation was 40%, the reduction of nicotine was only 25% and the reduction ratio of water was higher than 70%. Compared with the ISO smoking regime, the yield of nicotine increased by 97% and the yield of water increased by 549% under HCI smoking regime. Compared with the ISO smoking regime, both the higher puff volume and puff frequency of the HCI regime resulted in significantly increased yields of water. The results were in accordance with the ISO technical report (24).

In Table 6, it can be seen that the amount of organic acids retained in the filter is higher than the yield in mainstream cigarette smoke. This might be because organic acids contain carboxyl groups and are easily retained on the surface of CA. When the filter ventilation is increased, the retention of organic acids also decreases, and the degree of reduction of different organic acids is also different. For example, when the filter ventilation was 40%, the reduction of formic acid in filter retention was 39%, and the reduction of palmitic acid was only 5%. This also indicates that the smoke retention is not only influenced by smoke dilution, but is also related to spatial distribution in the filter. Comparing the ISO and the HCI smoking regime, with the increase of puff volume, the retention of all organic acids increased, but also to different extents, e.g., the retention of formic acid increased by 138%, and the retention of oleic acid only increased by 1.5%. In addition, the retention of benzoic acid increased by 120% when switching from the ISO to the HCI smoking regime, and the retention of other organic acids with similar BP and MW did not increase as much. This might be due to the weak polarity of benzoic acid and strong interaction with CA.

Table 7 shows the filter retention of routine smoke components at different filter ventilation levels under the ISO smoking regime and a comparison between the ISO and the HCI smoking regimes. It could be found that more water was retained in the filter than the yield in mainstream cigarette smoke. That might be due to the fact that CA has a certain degree of water absorption. With the increase of filter ventilation, the nicotine and water content in the filter decreased, but the degrees were significantly different. Comparing cigarettes with 0% and 40% filter ventilation, the filter retention of nicotine was only reduced by 9.6%, and the filter retention of water was reduced by 80%.

Comparing the results obtained with the ISO and the HCI smoking regimes, the filter retention of nicotine increased by 96% and of water increased by as much as 815%.

Figure 3 shows the patterns of filter retention for formic acid at different filter ventilation levels. For unventilated cigarettes, the radial distribution of formic acid is concentrated in the middle of the filter, while longitudinally the concentration at the mouth end is higher than at the tobacco rod end, owing to the low BP and low MW of formic acid. It could also be found that the filter ventilation resulted in a significant decline of formic acid concentration on the periphery part and mouth end of the filter. Compared with the ISO smoking regime, the HCI regime causes an increase in the retention of formic acid in the filter, and the retention distribution is also slightly different.

Figure 3

The retention spatial concentration distribution patterns of lactic acid at different filter ventilation levels under ISO and HCI smoking regime are displayed in Figure 4. The influence of filter ventilation on the retention and distribution of lactic acid is similar to that of formic acid. With the increase of ventilation, the distribution of lactic acid was also more concentrated in the middle of the filter. Compared with the ISO smoking regime, in the HCI regime, the retention distribution of lactic acid was also more concentrated in the central area of the filter.

Figure 4

Palmitic acid has a higher BP and a larger MW than most other organic acids in this investigation, and its distribution in the filter is concentrated at the tobacco end of the filter. It can be seen from the Figure 5 that the filter ventilation had little effect on the retention and distribution of palmitic acid. The retention patterns of palmitic acid under ISO and HCI smoking regimes are also very similar.

Figure 5

As shown in Figures 6 and 7, the distribution of nicotine and water in the filter are significantly different. The distribution of nicotine is concentrated in the middle part and the tobacco rod end of the filter. Therefore, the filter ventilation and smoking regime have less influence on the distribution of nicotine in the filter.

Figure 6

Figure 7

Compared with nicotine, the BP and MW of water are lower. Therefore, the concentration of water in the lower temperature part at the mouth end and the peripheral part of the filter is higher. When the filter was ventilated, the concentration distribution of water was greatly affected. In addition, the HCI smoking resulted in higher water delivery and the concentration of water obviously increased at the mouth end of the filter. A photograph of cigarette filters at different filter ventilation levels after smoking is shown in Figure 8. It can be seen that filter ventilation has a significant effect on the retention of smoke. That is, the cigarette filter ventilation led to a reduction of the concentration of smoke aerosols in the peripheral part of the filter.

Figure 8

Photographs of the 40% ventilated cigarette filter after a puff of smoking are shown in Figure 9. It can be seen that the smoke diffused into the environment from the ventilation holes and the mouth end of the filter within 1 second after a puff of smoking. Therefore, the diffusion effect of chemical components with higher concentration distribution in these regions was also more significant. Under the HCI smoking regime, the ventilation holes are blocked, and the components with a high concentration distribution at the mouth end of the filter are more likely to diffuse into the mainstream smoke. As illustrated in Figure 10, a possible model for smoke diffusion in ventilated cigarette filter is proposed. When the filter is ventilated, the air compression and the smoke diffusion effect are generated around the vent holes.

Figure 9

Figure 10

In the ISO smoking regime, the puff profile is bell-shaped, and the smoke flow velocity is relatively fast for a short time (1–1.5 seconds). At this period, the air compression effect is obvious. With the flow velocity drops, the diffusion effect will become prominent. The diffusion of smoke will also continue for a period of time, about 2–3 seconds, after the end of each puff of smoking, due to the inertial effect of the smoke aerosol. Due to the smoke diffusion, the smoke concentration at the periphery part and smoking end of filter was greatly reduced.

As a result, the chemical components with a higher retention concentration in this part were more likely to diffuse into the environment, and finally caused an obvious decrease in the mainstream smoke. Owing to the air compression, the smoke concentration on the middle part was less affected. Therefore, the retention of these chemical components was not changed obviously, and the amount of these components entering the mainstream smoke was only affected by smoke dilution.