LABORATORY EXPERIMENT pubs.acs.org/jchemeduc
Determination of Carbon Dioxide, Carbon Monoxide, and Methane Concentrations in Cigarette Smoke by Fourier Transform Infrared Spectroscopy T. L. Tan* and G. B. Lebron Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Singapore
bS Supporting Information ABSTRACT: The integrated absorbance areas of vibrational bands of CO2, CO, and CH4 gases in cigarette smoke were measured from Fourier transform infrared (FTIR) spectra to derive the partial pressures of these gases at different smoke times. The quantity of the three gas-phase components of cigarette smoke at different smoke times were then determined. The concepts and applications of the FTIR spectroscopic technique, the BeerLambert law, infrared band strengths, emission rates of gases, ideal gas law, and experimental hazards were effectively demonstrated and discussed for a laboratory experiment intended for upperdivision undergraduate chemistry students. KEYWORDS: Upper-Division Undergraduate, Analytical Chemistry, Environmental Chemistry, Laboratory Instruction, Physical Chemistry, Hands-On Learning/Manipulatives, Drugs/Pharmaceuticals, Fourier Transform Techniques, Gases, Laboratory Equipment/Apparatus
F
ourier transform infrared (FTIR) spectrometers of spectral resolution of 0.5 to 16 cm1 are now routinely used to record good quality infrared (IR) spectra for studies on solids, liquids, and gases in chemistry laboratory courses. Traditionally, undergraduate chemistry students are first introduced to FTIR spectroscopy when they take organic chemistry laboratory or instrumental analysis courses. Students are reacquainted with FTIR spectroscopy in physical chemistry laboratory work. A steady stream of physical chemistry FTIR experiments has appeared in this Journal.113 In an experiment by Reeve and co-workers,2 cigarette smoke was used as a sample source to analyze the FTIR spectra of CO, CH4, and HCN found in cigarette smoke. In another cigarette smoke analysis using an inexpensive IR gas cell constructed by the authors, different gaseous species were identified by their vibrational peak positions.3 An FTIR experiment is described for upper-level chemistry students that makes use of cigarette smoke as a sample source, that uses an easy-to-construct IR cell to contain the smoke, and employs the concept of band strengths to determine the amount of CO2, CO, and CH4 gases in cigarette smoke.
which could be fitted into the sample chamber of an FTIR spectrometer, has a small hole in front through which a lit cigarette is inserted and held in place. As the smoke was continuously introduced into air inside the chamber by a lit cigarette placed in it, the FTIR spectra were recorded at 2 or 3 min intervals for 13 min. A total of six spectra at different time intervals were obtained to determine the concentrations of the gases in the smoke during these intervals. The spectra were recorded using a Perkin-Elmer Spectrum One spectrometer at a resolution of 4 cm1 in the 4000400 cm1 range. For each spectrum, 20 scans were sufficient to give a signal-to-noise ratio of more than 15. A thermometer was used to measure room temperature. If the class is divided into several groups and each group is given a cigarette stick as sample, it would approximately take 20 to 30 min for a group to the complete the spectral data collection. A three-hour laboratory session is sufficient with groups taking turns in collecting and recording their spectral data. The typical FTIR absorbance spectrum of cigarette smoke (Figure 1) shows the CO2 bands at 669 and 2349 cm1, the CO band at 2144 cm1, and the CH4 band at 3017 cm1.
’ EXPERIMENTAL DETAILS A 20 cm 20 cm 20 cm smoke box fabricated from poly(methyl methacrylate) with KBr windows (5 cm diameter) installed on opposite sides was used to contain the smoke from the cigarette. A similarly constructed chamber with CaF2 IR windows was used in the study of decay rate of carbon monoxide.14 The smoke box,
’ HAZARDS The high levels of concentrations of CO gas inside the smoke chamber exceed the maximum limit of 200 ppm allowed
Copyright r 2011 American Chemical Society and Division of Chemical Education, Inc.
Published: November 17, 2011 383
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Figure 1. The FTIR spectrum of cigarette smoke recorded at a resolution of 4 cm1.
Figure 2. Emission rates of CO2, CO, and CH4 in cigarette smoke.
according to WHO guidelines for CO.15 The CH4 gas in the smoke chamber is easily ignited and highly flammable in the presence of nearby spark or fire. Cigarette smoke contains high levels of nicotine, tar, and other particulates and gases. During experiments, the cigarette smoke should not be released into the laboratory. After the experiments, release the cigarette smoke slowly into the air in an open and spark-free environment outside the laboratory away from people
Table 1. Partial Pressures, Masses, and Concentrations of CO2, CO, and CH4 in Cigarette Smoke CO2
’ RESULTS AND DISCUSSION Integrated absorbance areas of the bands of CO 2 in 620715 cm 1 , CO in 20302240 cm 1 , and CH 4 in 28003200 cm1 were measured for six different burning times of the cigarette sample. The software bundled with the FTIR spectrometer was used by the students to determine the area under each of the absorption bands belonging to the different gases in the absorbance spectra of the cigarette smoke. The linear variations of integrated absorbance areas of CO2, CO, and CH4 with time are shown in Figure 2. The BeerLambert law in the gas phase16 and the equation for band strength Sb17,18 are given as A ¼ αpl Sb ¼
1 pl
absorbance
partial
mass/
concentration
time/min
area/cm1
pressure/Pa
mg
(ppm)
3
3.4741
86.9
12.4
1303.7
5
5.985
149.1
21.3
2236.0
6
6.2272
155.8
22.3
2336.8
8 10
9.6294 12.9059
240.9 322.9
34.5 46.2
3613.5 4843.1
13
16.2815
407.3
58.3
6109.8
CO
ð1Þ
Z υ dυ
cigarette smoke
cigarette smoke
absorbance
partial
mass/
concentration
time/min
area/cm1
pressure/Pa
mg
(ppm)
3
1.1613
22.1
2.01
211.1
5
1.8595
35.4
3.22
338.0
6
1.9143
36.5
3.32
348.0
8 10
3.0835 4.0509
58.7 77.1
5.35 7.02
560.5 736.4
13
5.0763
96.7
8.80
922.8
ð2Þ
CH4
where A is the absorbance, α is the absorbance coefficient of the gas, p is the partial pressure of the gas, l is the R optical path length, Sb is the band strength or intensity, and υ dυ represents the integrated area of absorbance. The Sb values for CO2 at 669 cm1, CO at 2144 cm1, and CH4 at 3017 cm1 are given as 202.45 ( 0.29 atm1 cm2,19,20 266 ( 3.4 atm1 cm2,21 and 269.92 ( 2.5 atm1 cm2,22 respectively. From these known values of Sb, l = 20.0 cm, and integrated area of absorbance, A = R υ dυ determined from the spectra, the partial pressure p of each gas-phase component can be calculated as follows: Z 1 A ð3Þ υ dυ ¼ p¼ Sb l Sb l
cigarette smoke
absorbance
partial
mass/
concentration
time/min
area/cm1
pressure/Pa
mg
(ppm)
3
0.9211
17.3
0.90
94.5
5
1.2715
23.9
1.24
130.5
6
1.4572
27.3
1.43
149.5
8
1.9894
37.3
1.95
204.1
10 13
2.5103 3.1723
47.1 59.5
2.46 3.10
257.6 325.5
To find the mass of the gas, the ideal gas equation was used. Because the partial pressures of the gases are low, ideal gas condition can be assumed,
The relationships between absorbance, band strength, and concentrations are explained in refs 23 and 24.
pV ¼ nRT 384
ð4Þ dx.doi.org/10.1021/ed200178s |J. Chem. Educ. 2012, 89, 383–386
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where m is the mass of the gas or air, p is pressure of gas or air, and mm is the molar mass of the gas or air. Derivation of eq 5 is given in the Supporting Information for this experiment. The pressure of the smoke in the chamber is taken as 1.0 atm or 1.013 105 Pa. Typical experimental results for a 13 min cigarette smoke time are presented in Table 1. The variations in concentrations of CO with CO2, CO with CH4, and CO2 with CH4 are shown in Figures 3, 4, and 5, respectively. It is instructive to show that linear relationships were observed for all three variations of gas concentrations as this linear relationship between concentrations of gases emitted from the same source is well documented. For instance, the linear variation of CO with CO2 concentrations was observed for the air collected from a city traffic tunnel in Chile.25 Also, the concentration of CO was shown to increase linearly with the concentration of nicotine in environmental tobacco smoke in restaurants in Finland.26 Finally, in an indoor car park in Hong Kong,27 the concentration of isoprene gas was found to increase proportionally with that of 1,3-butadiene.
Figure 3. Variation of concentration of CO with that of CO2.
’ ASSOCIATED CONTENT
bS
Supporting Information Instructor notes; student notes; derivation of eq 5. This material is available via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. Figure 4. Variation of concentration of CO with that of CH4.
’ ACKNOWLEDGMENT The authors are indebted to the financial support of this project by the National Institute of Education, Singapore through Research Grants RS 3/08 TTL and RI 9/09 TTL. ’ REFERENCES (1) Dierenfeldt, K. E. J. Chem. Educ. 1995, 72 (3), 281–283. (2) Ford, A. R.; Burns, W. A.; Reeve, S. W. J. Chem. Educ. 2004, 81 (6), 865. (3) Garizi, N.; Macias, A.; Furch, T.; Fan, R.; Wagenknecht, P.; Singmaster, K. A. J. Chem. Educ. 2001, 78 (12), 1665–1666. (4) Bozlee, B. J.; Luther, J. H.; Buraczewski, M. J. Chem. Educ. 1992, 69 (5), 370. (5) Briggs, A. G. J. Chem. Educ. 1970, 47 (5), 391. (6) Bryant, M. S.; Reeve, S. W.; Burns, W. A. J. Chem. Educ. 2008, 85 (1), 121. (7) Castle, K. J. J. Chem. Educ. 2007, 84 (3), 459. (8) David, C. W. J. Chem. Educ. 1996, 73 (1), 46. (9) Fetterolf, M. L. J. Chem. Educ. 2007, 84 (6), 1062–1066. (10) Hollenberg, J. L. J. Chem. Educ. 1966, 43 (1), 7. (11) Keedy, C. R. J. Chem. Educ. 1992, 69 (11), A296. (12) Sorkhabi, O.; Jackson, W. M.; Daizadeh, I. J. Chem. Educ. 1998, 75 (2), 238–240. (13) Woods, R.; Henderson, G. J. Chem. Educ. 1987, 64 (11), 921–924. (14) Tan, T. L.; Lebron, G. B. Urban Air Quality Management: Detecting and Improving Indoor Ambient Air Quality. In Eco-city Planning: Policies, Practice and Design, 1st ed.; Wong, T.-C., Yuen, B., Eds.; Springer: Dordrecht, The Netherlands, 2011. (15) WHO. Environmental health criteria, no. 213: carbon monoxide, http://www.who.int/pcs/ehc/summaries/ehc_213.html (accessed Oct 2011).
Figure 5. Variation of concentration of CO2 with that of CH4.
where V is the volume of the gas, n is the number of moles, R is the gas constant, and T is the temperature. The volume V of the gas was actually the volume of the smoke chamber, which is 0.0080 m3. The partial pressure p was derived earlier, and the temperature T of the gas was 296 K (room temperature). The concentration C, expressed in parts-per-million (ppm), of the gas-phase component of the cigarette smoke in air is calculated using ! mgas pgas mmgas 6 10 ¼ 106 ð5Þ Cðin ppmÞ ¼ matr patr mmair 385
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