ARTICLE pubs.acs.org/ac
Online Comprehensive Two-Dimensional Characterization of Puff-byPuff Resolved Cigarette Smoke by Hyphenation of Fast Gas Chromatography to Single-Photon Ionization Time-of-Flight Mass Spectrometry: Quantification of Hazardous Volatile Organic Compounds Markus S. Eschner,†,‡ Ismailhaki Selmani,†,‡ Thomas M. Gr€oger,†,‡ and Ralf Zimmermann*,†,‡,§ †
Joint Mass Spectrometry Centre, Cooperation Group “Comprehensive Molecular Analytics”, Helmholtz Zentrum M€unchen, Ingolst€adter Landstrasse 1, 85764 Neuherberg, Germany ‡ Chair of Analytical Chemistry, Institute of Chemistry, University of Rostock, Dr.-Lorenz-Weg 1, 18059 Rostock, Germany § Environmental Chemistry, Bavarian Institute of Applied Environmental Research and Technology GmbH, Am Mittleren Moos 46, 86167 Augsburg, Germany ABSTRACT: This work presents the direct coupling of a custom-made smoking machine (SM) to fast gas chromatography combined with single-photon ionization mass spectrometry (GC SPI-MS) utilizing a six-port, two-position valve for online puff-resolved comprehensive two-dimensional investigation of cigarette smoke. The innovative electron-beam pumped rare gas excimer light source (EBEL) filled with argon provided vacuum ultraviolet (VUV) photons of 9.8 ( 0.4 eV (126 ( 9 nm) for SPI. Puff-by-puff quantification of 14 hazardous volatile organic smoke constituents from the 2R4F Kentucky research cigarette was enabled for two smoking regimes, i.e., ISO and Canadian Intense, after determination of photoionization cross sections. The investigated analytes comprised NO, acetaldehyde, butadiene, acrolein, propanal, acetone, isoprene, furan, crotonaldehyde, isobutanal, butanal, 2-butanone, benzene, and toluene. The determined amounts of these compounds in cigarette smoke agreed excellently with the literature values. Furthermore, the two well-known patterns of puff-bypuff behaviors for these different smoke constituents were obtained for both whole smoke and gas-phase measurements.
C
igarette smoke represents a very complex matrix consisting of diverse compound classes like hydrocarbons, aldehydes, ketones, heterocycles, and others beside the major components carbon dioxide, carbon monoxide, water, and air. More than 4800 different smoke constituents have been identified so far.1 Furthermore, whole cigarette smoke is an aerosol composed of a gas phase and a particulate phase, while many substances are dispersed between both phases. The gas phase consists of just about 400500 individual compounds in a wide concentration range, whereas many of them are toxic and/or carcinogenic.2 Hence, the majority of smoke constituents appear in the particulate fraction covering a diversity of organic compounds. In tobacco science quartz fiber filter pads, so-called Cambridge filter pads, are usually applied for collecting the particulate phase of cigarette smoke resulting in a separation from the gas phase.3 The Cambridge filter traps particles larger than 0.1 μm present in the cigarette smoke aerosol with 99.9% efficiency while gas-phase smoke components pass through the filter.4 Cigarette smoke analysis is mostly performed by application of well-established off-line techniques such as liquid chromatography (LC) and gas chromatography (GC).1 However, these conventional analytical methods can lead to an alteration of the smoke composition caused by sample preparation steps such r 2011 American Chemical Society
as trapping, extraction, and derivatization as well as during separation which typically takes several minutes. Furthermore, smoke is usually collected from a whole cigarette or sometimes even several cigarettes resulting in the loss of information about smoke dynamics and variations in concentration during the smoking process. Since some smoke components are very reactive, leading to a constantly changing mixture, it is important to analyze fresh rather than aged smoke. Moreover, further improvements of the separation efficiency in the field of gas chromatography leading to comprehensive two-dimensional (2D) gas chromatography (GC GC)510 showed that more than 10 000 substances might be present in cigarette smoke.11 The advantages of GC GC over conventional one-dimensional (1D) GC are increased selectivity due to the second separation mechanism involved, high sensitivity because of the modulation process, and ordered dispersion of structurally related components in the 2D chromatogram. This typical compound class grouping simplifies identification and allows rapid screening of unknowns according to their appearance in the 2D separation Received: April 27, 2011 Accepted: June 24, 2011 Published: June 24, 2011 6619
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Figure 1. Photograph and sketch of the two-dimensional smoke analysis system consisting of a home-built smoking machine (SM), a gas chromatograph (GC), and a single-photon ionization mass spectrometer (SPI-MS). (a) Photograph of the SMGC SPI-MS instrument, including personal computer, power supplies, and control; the EBEL light source is displayed in the inset in the upper right corner. (b) Schematic representation of the smoke analyzer: (1) original Borgwaldt smoking valve; (2) particle filter; (3) smoking pump; (4) sampling pump; (5) six-port, two-position valve; (6) sample loop.
Figure 2. Illustration of the two positions of the six-port valve during (a) smoking/sampling and (b) separation. Connections at the valve ports are as follows: (1) metal transfer line from the original Borgwaldt smoking valve, (2) capillary to sampling pump, (3 and 6) sample loop, (4) capillary from the GC injector, and (5) analytical column.
plane. In addition, time-of-flight mass spectrometric (TOFMS) detection further facilitated the identification of constituents in the particulate phase of cigarette smoke.1214 Recently, GC GC/TOFMS combined with straightforward types of data analysis methods enabled the investigation of cigarette particulate matter originating from different types of cigarettes on a puffby-puff basis.15 First investigations of puff-by-puff resolved cigarette smoke were reported by Vilcins, who quantified ethylene and isoprene in the gas phase by application of infrared spectroscopy.16 Since then, several analytical techniques have been employed for single puff or puff-by-puff characterization of smoke components such as Fourier transform infrared spectroscopy (FTIR),17,18 infrared tunable diode laser (TDL) spectroscopy,19,20 infrared tunable diode laser absorption spectroscopy (IRTDLAS),21,22 and gas chromatography mass spectrometry (GC/MS).23,24 However, most of these approaches suffer from either the low time resolution or the limited number of substances being analyzed simultaneously. Single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS)2527 has shown to be well-suited for monitoring multiple gaseous and semivolatile compounds in cigarette smoke
on a puff-resolved basis.28 Soft photoionization was performed using frequency-multiplied Nd:YAG laser pulses of 118 nm (10.49 eV). Furthermore, puff-by-puff quantification of several toxic and carcinogenic smoke constituents was realized using standard gases for calibration.29,30 Recently, the influence of filter ventilation on the formation of different smoke constituents was also investigated.31 However, the mass resolution of 1800 of the applied TOFMS was insufficient to distinguish between isobaric compounds like isoprene and furan. Moreover, functional isomers such as ketones and aldehydes, both with the same molecular formula (CnH2nO), could not be differentiated either. Though, discrimination between such isobaric and isomeric compounds concerning a classification of the toxicological risks of smoke originating from different types of cigarettes is very desirable. The present work describes the combination of a custommade smoking machine with fast gas chromatography coupled to SPI-TOFMS for online comprehensive two-dimensional characterization of puff-by-puff resolved cigarette smoke. This approach allows the differentiation of several isobaric as well as isomeric compounds. Furthermore, quantification of 14 hazardous smoke constituents was realized for two different smoking regimes. 6620
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Figure 3. Puff-by-puff characterization of whole smoke of a 2R4F Kentucky research cigarette smoked under ISO conditions. (a) Two-dimensional contour plot of molecular mass against gas chromatographic retention time of the first three puffs. (b) Summed mass spectra of the third puff (marked by the bright rectangle in panel a. (c) Time profiles of three selected masses indicated by the brown (m/z 56), red (m/z 58), and green (m/z 68) line in panel a.
’ EXPERIMENTAL SECTION Analytical Instrumentation. Figure 1 exhibits both a photograph and a sketch of the analysis system consisting of a custommade smoking machine coupled to a gas chromatograph/timeof-flight mass spectrometer with soft single-photon ionization capability (SMGC SPI-TOFMS). The original smoking valve of a Borgwaldt KC GmbH (Hamburg, Germany) single-port smoking machine was installed between the cigarette holder and a heated Swagelok T-piece adapter. A membrane pump (KNFNeuberger, Munich, Germany) was utilized to adjust a continuous flow rate of either 1.05 L/min (35 mL/2 s) or 1.65 L/min (55 mL/2 s), depending on the desired smoking regime, which was monitored by a flow meter unit. Furthermore, a particle filter prevented the sampling pump of contamination with unfiltered smoke. For guiding a portion of the cigarette smoke into the gas chromatograph an inert MXT guard capillary (1.25 m 0.28 mm) from Restek GmbH (Bad Homburg, Germany) was directly inserted into the smoke flow at the T-piece connection and was permanently heated to 250 °C. By means of a second membrane pump a constant flow of 4 mL/min was drawn through this metal capillary, which was connected to a VICI six-port, two-position valve (Valco Instruments Inc., Houston, TX) equipped with a sample loop (25 cm 1 mm, stainless steel). The injector of the gas chromatograph Varian 450 GC (Varian Inc., Palo Alto, CA, U.S.A.) was also connected to the VICI valve (prospectively termed sampling valve) and provided He as carrier gas for separation of smoke analytes using the ionic liquid column SLB-IL59 (15 m 0.25 mm 0.2 μm) from Supelco (Bellefonte, PA). The separated analytes were guided by a deactivated transfer line capillary (0.5 m 150 μm), which was permanently heated to 250 °C, to the ionization region of the
orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS; Tofwerk AG, Thun, Switzerland). The MS enabled two ionization modes: classical 70 eV electron ionization (EI) and soft single-photon ionization (SPI) based on the compact electronbeam pumped rare gas excimer light source (EBEL).3234 The properties of the GC SPI-MS system and its application in comprehensive multidimensional investigations of diesel fuel were previously described as well.35,36 Smoking Conditions. In this study the standardized and wellcharacterized23,37,38 2R4F research cigarette available from the University of Kentucky, Kentucky Tobacco Research and Development Center (KTRDC) was investigated concerning hazardous volatile organic compounds. Prior to analysis these research cigarettes as well as Cambridge filter pads (used for gas-phase measurements) were stored for a minimum of 4 days under controlled conditions of 60% relative air humidity and 22 °C.4 Both whole smoke (without a Cambridge filter pad) and gasphase measurements were performed by applying the smoking procedure according to the International Organization for Standardization (ISO) conditions (35 mL puff volume, 2 s puff duration, 60 s puff interval, no blocking of filter ventilation holes).4 In addition to the ISO smoking regime the Canadian Intense parameters (55 mL puff volume, 2 s puff duration, 30 s puff interval, 100% blocking of filter ventilation holes) were also employed for investigation of the gas phase. These more intense conditions are thought to better match human smoking behavior. All cigarettes were lit with a common butane gas lighter. Sampling and Separation Procedure. Since smoke compounds are introduced for separation in a pulsed manner a six-port, two-position valve equipped with a sample loop turned out to be especially suited for a comprehensive two-dimensional investigation 6621
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Table 1. Photoionization Cross Section Data of Selected Smoke Constituents for Ionization with the Ar-EBEL Light Source and Respective Limits of Detection m/z
PICS [Mb]
relative PICS
NO
30
1.4
0.071
450
acetaldehyde
44
0.15
0.0078
4100
1,3-butadiene
54
8.8
0.45
71
acrolein
56
0.71
0.036
890
propanal acetone
58 58
1.8 6.1
0.091 0.31
350 100
isoprene
68
13.0
0.66
48
furan
68
10.6
0.54
59
crotonaldehyde
70
3.5
0.18
180
isobutanal
72
2.2
0.11
290
butanal
72
2.0
0.10
320
2-butanone
72
9.4
0.48
67
benzene toluene
78 92
19.6 22.5
1.00 1.15
32 28
substance
Figure 4. Absolute photoionization cross sections (PICS) of 10 different smoke constituents including unsaturated hydrocarbons, ketones, aldehydes, and unsaturated aldehydes.
of these analytes. The connections at the ports are as follows: (1) metal transfer line from the original Borgwaldt smoking valve, (2) capillary to sampling pump, (3 and 6) sample loop, (4) capillary from the GC injector (He inlet), and (5) analytical column (see Figure 2). By means of an in-house-built control unit and a homewritten LabView script (National Instruments, Austin, TX) the original Borgwaldt smoking valve as well as the sampling valve can be operated automatically. Figure 2a depicts the position of the sixport valve during smoking/sampling. Ports 1 and 6 as well as 2 and 3 are connected enabling the sampling pump to draw a portion of smoke into the sample loop (flow of smoke is indicated by red arrows), while simultaneously a flow of He (indicated by black arrows) is driven through the analytical column since ports 4 and 5 are connected as well. Automatically 1 s after a puff has been completed the sampling valve is turned to the separation position illustrated in Figure 2b. Now, ports 3 and 4 as well as 5 and 6 are connected enabling the injection of the previously captured portion of smoke into the ionic liquid column by the applied He flow. This position is maintained for separation until the next puff is taken. Gas Chromatographic and Mass Spectrometric Parameters. Since the separation of the smoke compounds of each individual puff has to be fast due to the regulations of the smoking regimes (60 s for ISO and 30 s for Canadian Intense) an injector pressure of 400 kPa for ISO and 500 kPa for Canadian Intense measurements was applied. Furthermore, the length of the ionic liquid column was reduced to 15 m to provide a sufficient separation of the isobaric compounds isoprene and furan without the use of external coolant. Moreover, this study is focused on volatile organic compounds present in cigarette smoke, and therefore, an isothermal oven temperature of 40 °C was set for both smoking regimes. After smoking of each cigarette the GC oven was heated up to 250 °C for 15 min to remove compounds with higher boiling points, first of all nicotine for whole smoke measurements, from the analytical column. The extraction frequency of the oaTOFMS was set to 80 kHz for covering a mass range of m/z 15340 at a final acquisition rate of 20 Hz. All quantified data presented here were determined by SPI using a home-built EBEL with argon as filling gas. This type of excimer light source generates an intense vacuum ultraviolet (VUV) radiation band with a central wavelength of 126 nm (9.8 eV) at a full width at halfmaximum (fwhm) of 9 nm. Data Postprocessing. The acquired mass spectra stored in hierarchical data format (“hdf5”) were directly loaded into MatLab 7.9.0.529 2009b (The Mathworks, Natick, MA,
LOD [pg]
U.S.A.) without any preceding transformation. Subsequent data processing was performed on a standard personal computer (2.16 GHz CPU, 2.87 GB RAM) by means of a MatLab script written in-house. All presented figures were further edited using Adobe Illustrator CS3 13.0.2 (Adobe System Inc., San Jose, CA, U.S.A.) to generate publicationready images.
’ RESULTS AND DISCUSSION Online Comprehensive Two-Dimensional Separation of Cigarette Smoke. Similar to GC GC, also with comprehen-
sive gas chromatography soft ionization mass spectrometry (GC MS) using SPI35,39 or field ionization (FI)40,41 structured 2D chromatograms are obtained. Usually, comprehensive 2D methods are applied for off-line analysis. Lately, Grobler et al.42 and van Geem et al.43 employed GC GC for online analysis of petrochemical samples in product streams during operation using valve-based injection systems for separation. More recently, GC SPI-MS was utilized for online investigation of evolved gases from a thermobalance.44 By means of a two-jet CO2 modulator analytes were trapped, refocused, and injected into a medium polar GC column. Now a similar approach was developed for analyzing cigarette smoke on a puff-by-puff basis. A custom-made smoking machine (SM) was coupled to a GC/ EBEL-SPI-MS system by a heated transfer line connected to a six-port, two-position valve (see the Experimental Section). Therefore, smoke constituents of each single puff were characterized by two parameters, i.e., GC retention time and molecular mass. Figure 3a represents a quasi-comprehensive 2D separation of the first three puffs of whole smoke of a 2R4F Kentucky research cigarette smoked under ISO conditions. Figure 3b exhibits the summed mass spectrum of the third puff, marked by the bright rectangle in Figure 3a. A similar mass spectrum would be obtained if solely mass spectrometric detection with SPI is applied. This well-described approach of coupling a smoking machine to a SPI-MS instrument28,29 already enables the monitoring of different smoke constituents as indicated by the structural formulas assigned to some peaks in the mass spectrum. However, as discussed already in the introduction, 6622
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Figure 5. Puff-by-puff amounts and total yields per cigarette of 14 volatile smoke constituents for whole smoke (blue) as well as gas phase (orange) of the 2R4F Kentucky research cigarette smoked under ISO conditions.
isobaric compounds like isoprene/furan and functional isomers like propionaldehyde/acetone cannot be distinguished by such an approach. However, these substances can be separated according to their different gas chromatographic behaviors (see Figure 3c). Figure 3c displays exemplarily time profiles of three selected masses indicated by the brown (m/z 56), the red (m/z 58), and the green (m/z 68) lines in Figure 3a. Now, acrolein can be separated from 1-butene as well as propionaldehyde from
acetone. Using the ionic liquid column SLB-IL59 even isoprene and furan are baseline-separated within the time frame of 60 s defined by the ISO smoking conditions without the use of external coolant. Moreover, further examples of qualitative differentiation between isomeric and isobaric compounds were achieved (see Figure 3a). Assignment of the different smoke constituents was done by measurements of standard solutions (verification by retention time) as well as by investigation of the 6623
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Table 2. Total Yields (μg/cig.) of Smoke Constituents of the 2R4F Kentucky Research Cigarette Smoked under ISO Conditions substance
this work
Chen and Moldoveanu (ref 37)a
NO
262.8 ( 40.8
223.41
acetaldehyde
622.8 ( 103.3
560.48
1,3-butadiene
49.8 ( 7.9
29.94
acrolein
60.4 ( 6.2
58.77
Wagner et al. (ref 23)b
Adam et al. (ref 29) 309.6 ( 13.9
218.1 ( 27.8
562
527.1 ( 26.7
587.4 ( 83.2
38.5 ( 2.2
38.2 ( 12.7
583.74 ( 13.18
635 ( 65 37.1 33.8 ( 3.0 59.8 ( 7.5
43.92 52.6 ( 7.6
acetone
250.9 ( 34.4
isoprene
426.5 ( 69.4
furan
35.8 ( 6.4
crotonaldehyde
12.5 ( 1.8
46.9
43.96 ( 0.97
53.7 ( 5.7
264.74
248
261.62 ( 7.35
282 ( 29
297.68
391 385 ( 26
16.18
42.6 ( 3.6
butanal
11.1 ( 1.6
33.5 ( 4.7 80.0 90.4 ( 10.2
62.72 73.48 ( 1.44
benzene
42.1 ( 6.0
43.39
397.2 ( 15.3
341.2 ( 50.5
18.0 ( 9.1
32.8 ( 9.0
29.0
12.64 ( 0.21 70.6 ( 10.0
270.4 ( 28.7
19.7 ( 3.4
29.58
2-butanone
49.0 ( 8.7 265.1 ( 15.1
14.5
20.06 ( 0.87 isobutanal
50.8 ( 13.9
67.3
50.34 ( 1.61 propanal
Intorp et al. (ref 38)
51.8
72.5 ( 17.5 48.2 ( 3.6
41.8 ( 9.4
84.5 ( 4.3
65.0 ( 19.6
48.2 ( 3.1 toluene
63.3 ( 9.5
64.91
88.0 82.8 ( 6.0
a
Chen and Moldoveanu’s publication contained two values for some compounds because two different analytical techniques were used. b Wagner et al.’s publication contained two values for the listed compounds. One value is obtained from 60 cigarettes (average of three replicates, each comprised 20 cigarettes), and the other over 2 or more years.
first puff of a 2R4F Kentucky research cigarette with GC/EI-MS (data not shown). In doing so, the analysis of a single puff lasted 30 min since the oven temperature was started from 40 °C and increased with 10 °C/min to 260 °C (verification by mass spectral library search and elution order). Quantification of Hazardous Volatile Organic Compounds Contained in Smoke of the 2R4F Kentucky Research Cigarette. Several tobacco smoke components are considered to be relevant to smoking-related diseases. The most comprehensive lists are those published by Hoffmann and co-workers.4547 Furthermore, additional lists of smoke carcinogens are available in the literature.4850 Moreover, quantitative rankings of cigarette smoke components concerning their health risks are given by Vorhees et al.,51 Fowles and co-workers,52,53 as well as Rodgman and Green.54 All reports declared 1,3-butadiene as the most carcinogenic agent and acrolein as the most toxic constituent in tobacco smoke. With this approach both compounds can be quantified online on a puff-by-puff basis. Since this approach is focused on online quantification of hazardous volatile smoke compounds by means of SPI-MS their photoionization cross sections (PICS) have to be known because ionization efficiency depends on the applied photon energy and the electronic structure of the analyte. Therefore, PICS of 10 smoke volatiles including unsaturated hydrocarbons, ketones, aldehydes, and unsaturated aldehydes were determined by means of the recently described GC SPI-MS
setup equipped with an Ar-EBEL.55 Figure 4 displays the results by plotting the molecular mass of each substance against the absolute PICS. Unsaturated hydrocarbons exhibit the highest PICS followed by the ketones and the aldehydes at the lower end. All values of these absolute PICS are listed in Table 1 together with the previously determined values of furan, benzene, and toluene. Furthermore, Table 1 contains also relative PICS with respect to benzene. The absolute PICS of NO for the used ArEBEL light source was determined from the data of Watanabe56 according to the method described in ref 55. Table 1 also contains the limits of detection (LOD) based on a signal-tonoise ratio of 3:1 for all investigated compounds. The rather high LOD for acetaldehyde (4.1 ng) is in this context advantageous because acetaldehyde is one of the major compounds in cigarette smoke and can be quantified easily without the risk of detector saturation. Recently, PICS of aromatic and oxygenated hydrocarbons have been measured by tunable synchrotron VUV light.57,58 Thus, quantification of these 14 hazardous compounds on a puff-by-puff basis was performed by the following procedure. Prior to analysis a known amount of benzene (mB) was introduced at the GC injector and after determination of the peak area (AB) the calibration factor fcal was calculated as follows: f cal ¼ mB =AB
ð1Þ
Subsequent to smoking and under consideration of the mass discrimination of the applied oaTOFMS (fMS(A)) the peak area 6624
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Figure 6. Puff-by-puff characterization of the gas phase of a 2R4F Kentucky research cigarette smoked under Canadian Intense conditions. (a) Twodimensional contour plot of molecular mass against gas chromatographic retention time of a complete cigarette. (b) Time profiles of three selected masses indicated by the brown (m/z 56), red (m/z 58), and green (m/z 68) line in panel a.
of each analyte (AA) was determined and divided by the relative PICS of the respective compound (σ0 A). After multiplication with fcal and under consideration of the respective split ratio (rsp) during smoking the amount for each puff of the analytes (mA) was obtained according to eq 2: mA ¼ ðf MS ðAÞÞðAA Þð1=σ 0 A Þðf cal Þðrsp Þ
ð2Þ
The total amount per cigarette was calculated by summation of all puff values. Figure 5 summarizes both puff-by-puff amounts and total yields per cigarette (μg/cig.) of the target compounds for whole smoke (blue) as well as gas phase (orange) of the 2R4F Kentucky research cigarette smoked under ISO conditions. In general, gas-phase yields were lower than those in whole smoke except for NO being totally in the gas phase of cigarette smoke. Furthermore, the two well-known patterns of puff-by-puff behaviors for different smoke constituents are obvious for both whole smoke and gas-phase measurements. Generally, most substances instancing NO, all ketones and aldehydes, furan, and toluene feature a constant increase in concentration from the first to the last puff. This trend is due to a steady reduction of tobacco rod length during consumption resulting in a decrease of filtration by the tobacco rod for particulate matter as well as reduction of condensation of gasphase compounds. Moreover, dilution with air and outward diffusion of gaseous products decline, too. The second group, represented by unsaturated hydrocarbons like 1,3-butadiene, isoprene, and benzene, exhibits high yields in the first puff while yielding lower levels for the second puff followed by an increase for the subsequent puffs. To evaluate the quantitative results obtained by this novel online GC MS approach for cigarette smoke characterization the total yields for the 2R4F Kentucky research cigarette were compared to literature values in Table 2. Generally, all
data are in excellent agreement with the previously published values. Furthermore, this approach allowed the quantitative differentiation of isoprene and furan as well as isobutanal, butanal, and 2-butanone on a puff-by-puff basis. In a previous report37 it is mentioned that isobutanal and butanal were not resolved with the used HPLC method, and the given value comprises the amount of both aldehydes. Furthermore, in the same publication it is stated that the value of isobutanal determined with a GC/MS method is about twice as high as for butanal. Besides the classical ISO conditions, this approach could also handle the Canadian Intense smoking regime, which is believed to better match human smoking behavior. Due to an increased injector pressure of 500 kPa the separation time could be further lowered while still maintaining a sufficient resolution. The quasi-comprehensive two-dimensional puffby-puff characterization of the gas phase of a 2R4F Kentucky research cigarette smoked under Canadian Intense conditions is shown in Figure 6a, while the time profiles of the same compounds as in Figure 3c are displayed in Figure 6b yielding still very good separation. Furthermore, quantification is performed according to the ISO measurements. The results are listed together with data from Mitschke59 and Counts et al.60 in Table 3. Unfortunately, Counts et al. investigated the 1R4F Kentucky research cigarette. Nevertheless, a comparison should be possible since this type of research cigarette yields almost the same values for smoke constituents under ISO conditions as the 2R4F Kentucky research cigarette does.37 However, the literature data are obtained from whole smoke measurements, and therefore, higher values were determined by the previous report.60 But when considering the gas-phase measurements under ISO conditions good agreement was obtained. Mitschke determined relatively high amounts for 6625
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Table 3. Total Yields (μg/cig.) of Vapor-Phase Measurements of the 2R4F Kentucky Research Cigarette Smoked under Canadian Intense Conditionsa substance NO
this work
Mitschke
Counts et al.
this work
(ref 59)
(ref 60)b
(ISO)
683 ( 50
612 ( 63
281 ( 24
582 ( 43 acetaldehyde
1162 ( 81
1,3-butadiene
97 ( 12
2796.2 ( 191.3
1448 ( 43
493 ( 25
147.1 ( 10.7
1359 ( 105 105.0 ( 6.9
39 ( 3
93.9 ( 9.2 acrolein
108 ( 16
122.4 ( 5.0
44 ( 4
111.2 ( 11.8 propanal
143 ( 24
128.9 ( 5.5
41 ( 3
115.6 ( 9.1 acetone isoprene
640 ( 29 797 ( 110
1005.8 ( 59.9
755 ( 27
202 ( 15
954.9 ( 70.9
687 ( 45 952 ( 73
317 ( 25
929 ( 68 furan
76 ( 8
crotonaldehyde
49 ( 7
30 ( 2 52.2 ( 3.0
8(1
49.1 ( 5.0 isobutanal butanal 2-butanone
115 ( 11
32 ( 3
26 ( 2
93.4 ( 2.3
9(1
121 ( 8
83.1 ( 6.1 209.0 ( 12.5
59 ( 3
189.7 ( 13.9 benzene
80 ( 6
118.7 ( 7.5
83.3 ( 8.2
40 ( 3
76.1 ( 9.1 toluene
121 ( 7
297.9 ( 16.6
176.2 ( 15.7
55 ( 4
156.3 ( 21.8 a
Literature values of whole smoke for the 2R4F (ref 59) and 1R4F (ref 60) Kentucky research cigarette. In the fifth row the vapor-phase yields under ISO conditions are listed for comparison. b Count et al.’s publication contained two values for the listed compounds because two data sets were investigated.
acetaldehyde which could not be explained.59 Generally, the amounts obtained under Canadian Intense smoking regime are about twice as high as under ISO conditions.
’ CONCLUSION AND OUTLOOK Gas chromatography coupled to SPI mass spectrometry (GC MS) using the innovative EBEL proved to be well-suited for online quasi-comprehensive two-dimensional characterization of puff-by-puff resolved cigarette smoke. In this study, 14 hazardous volatile organic compounds, i.e., NO, acetaldehyde, butadiene, acrolein, propanal, acetone, isoprene, furan, crotonaldehyde, isobutanal, butanal, 2-butanone, benzene, and toluene, were quantified according to their PICS and the standard benzene. In doing so, excellent agreement to previously published data was obtained for ISO and Canadian Intense smoking conditions. The typical “first puff high” behavior of unsaturated hydrocarbons as well as the constant increase for most of the other smoke constituents from the first to the last puff was also observed. Furthermore, by applying higher oven temperature or a low thermal mass GC with fast heating and cooling rates also semivolatile smoke constituents can be monitored online in a
quasi-comprehensive two-dimensional way in the future. Note that this setup, optimized for cigarette smoking requirements, can be further adapted to any kind of gas-phase monitoring such as breath analysis or process control of combustion, for example.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected], ralf.zimmermann@ helmholtz-muenchen.de. Phone: +49 (0) 381 498 6460. Fax: +49 (0) 381 498 6461.
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