Environ. Control Biol., 51 (1), 23 29, 2013
Original Paper
Fragmentation and Reaction Rate Constants of Terpenoids Determined by Proton Transfer Reaction-mass Spectrometry Akira TANI Institute for Environmental Sciences, University of Shizuoka, Shizuoka 422 8526, Japan (Received November 5, 2012; Accepted December 15, 2012)
Monoterpenes and oxygenated monoterpenes emitted by plants are involved in producing photochemical oxidants and secondary organic aerosols in the atmosphere. In the present study, the fragment patterns and the reaction rate constants of some of these compounds have been determined by proton transfer reaction-mass spectrometry (PTR-MS). Five monoterpenes (myrcene, camphene, -phellandrene, - and -terpinene) and two monoterpene alcohols (linalool and cineole) were observed to produce dominant ions of m/z 81 and 137 along with some minor m/z 67 and 95 ions. Myrcene, which is a straight-chained compound, produced an m/z 69 ion along with the above mentioned ions. A monoterpene ketone, thujone, has been found to produce a fragment ion, m/z 93. Since the m/z 69 and 93 ions are the protonated molecular ions of ubiquitous isoprene and toluene, respectively, these respective fragment ions may interfere with the quantification of both isoprene and toluene. We have also revealed that the proton transfer reaction rate is faster in the oxygenated monoterpenes (rate constant: 2.6 3.5×10−9 cm3 s−1) than in the common monoterpenes (2.22.4×10−9 cm3 s−1). This suggests that the calibration equation obtained from the relationship between the concentration and the produced ion count (m/z 81＋137) of selected monoterpenes may underestimate the total concentration of monoterpene alcohols and monoterpenes. Keywords : fragmentation, monoterpene, proton transfer reaction, PTR-MS, reaction rate constant
INTRODUCTION
Monoterpenes are the major secondary metabolites produced and emitted by plants. Once emitted to the atmosphere, they are involved in producing photochemical oxidants through a series of reactions with OH radical and NO. These reactions play an important role in influencing the atmospheric chemistry from the perspective of regional photochemical oxidant formation (Fall, 1999) and also in determining the lifetime of methane (Fehsenfeld et al., 1992). Recent studies have revealed that monoterpene oxidation products may significantly contribute to the formation of secondary organic aerosols (Miyazaki et al., 2012). Measurement of the atmospheric concentrations and biogenic emission rates of the monoterpenes and related VOCs are necessary for understanding their roles in plant biochemistry, plant physiology and atmospheric chemistry. Until recently, real-time analyses of these compounds were not very practical because of their low emission rates and low atmospheric concentrations. Hence, the majority of the analyses were earlier performed off-line, on preconditioned samples using gas chromatography either by flame ionization or by mass spectrometric detection. The development of the proton transfer reaction mass spectrometry (PTR-MS), in which protonated water (H3O＋) is used as the primary ionizing reactant, has enabled on-line monitoring of VOCs, including the monoterpenes and other related compounds (Lindinger et al., 1998; Hewitt et al.,
2003). PTR-MS has been used for measuring BVOC emission from plants (Tani et al., 2008; Okumura et al., 2008; Tani et al., 2011) and vegetation (Karl et al., 2001; Miyama et al., 2012) and as well, for measuring oxygenated VOC uptake by leaves of houseplants (Tani et al., 2007; 2009) and trees (Tani et al., 2010; Karl et al., 2010). The transfer of protons from H3O＋ to neutral entities can be regarded as “soft” ionization; under “normal” PTRMS operating conditions (detailed below), many of the VOCs are detected with a mass that is equal to their molecular mass plus one. Since the quadrupole of the PTRMS instrument can discriminate different masses but cannot distinguish between compounds that have the same mass, only the total concentration of all compounds with the same mass can be measured. In a forest atmosphere, more than 10 species of monoterpenes are usually found. Their total concentration can be determined by PTR-MS. However, the monoterpenes have been observed to undergo some degree of fragmentation within the instrument (Tani et al., 2003; Tani et al., 2004). It is thus, important to determine the fragment pattern of major individual monoterpenes as a function of the collisional energy E/N (where E is the electric field strength and N is the buffer gas number density in the drift tube). Beside monoterpenes, monoterpene alcohols and ketones are also emitted in large amounts by specific herbs and trees such as the Eucalyptus. Since molecular weight of monoterpene alcohols and ketones are 154 and 152, respectively, which are different from that of the
Corresponding author : Akira Tani, fax: ＋8154264 5788, e-mail :
[email protected] Vol. 51, No. 1 (2013)
( )
A. TANI
monoterpenes (m.w.＝136), they can be easily discriminated by quadrupole, simply if they produce significant proportion of protonated molecular ions (m/z 155 and 153 for monoterpene alcohols and ketones). However, only a few studies in the scientific literature have addressed the reaction of these compounds with H3 O＋ (Tani et al., 2003; Maleknia et al., 2007). A potential source of inaccuracy in a PTR-MS measurement of the common and oxygenated monoterpenes is the uncertainty in the proton transfer reaction rate constant values of the individual species. These values can be estimated using the parameterized trajectory formulation method developed by Su and Chesnavich (1982) that uses the dipole moment and the polarizability of the compounds. There is, however, very limited information available for the monoterpenes (Nelson et al., 1967; Zhao and Zhang, 2004). As a result, a nominal value of the proton transfer reaction rate constant (2.0×10−9 cm3 s−1) has widely been adopted for the PTR-MS quantification of monoterpenes. Owing to the different physico-chemical properties of individual monoterpenes, they may have different rate constants; it is thus highly desirable to determine the rate coefficient for all such individual monoterpene species so that their concentrations can be correctly measured. In the present study, we have used PTR-MS to investigate the fragmentation patterns of many of the monoterpene species and oxygenates. We also show how these fragmentation patterns are affected by different values of E/N in the drift tube. Using the relative rate constant determination method and simultaneous gas chromatography quantification of gaseous standards under varying concentrations, we obtain proton transfer reaction rate constants for the compounds with H3O＋ ions. Finally, we discuss the error in the determination of total monoterpene concentration caused by the fragmentation patterns of monoterpene families. EXPERIMENTAL METHODS
PTR-MS instrumentation PTR-MS has been described in detail elsewhere (Lindinger et al., 1998; Hewitt et al., 2003); therefore, only the points relevant to this paper have been described in this section. The PTR-MS instrument comprises three parts: (1) an ion source, (2) a drift tube (reaction chamber), and (3) an ion separation/detection system. In general, H3 O＋ ions formed in the hollow cathode ion source react with the neutrals (R) in the drift tube, resulting in the proton transfer reactions. This results in the production of RH＋ ions that are separated by a quadrupole mass spectrometer (Balzers QMG421) and detected and quantified in terms of ion counts per second (cps) by a secondary electron multiplier (Balzers QC422). Because the density of H3O＋ ions, i.e., [H3O＋] is high in the drift tube, and only a small fraction of the H3O＋ ions reacts with the neutrals, [H3O＋] remains constant, maintaining the pseudo-first order reaction kinetics. Under such conditions, the density of product ions [RH＋] is given by the following relation: ( )
H3O＋ Rk t RH＋ ＋
(1) ＋
where [H3O ] is the density of H3O ; [R], the molecular ion density of the trace component R; k, the reaction rate constant for the proton transfer reaction between R and H3O＋; and t, the time taken for H3 O＋ ions to traverse the drift tube. Standard preparation using diffusion system In order to identify the individual monoterpene fragment patterns, to investigate the effects of the collisional energy on these patterns, and to experimentally determine the rate constants, a diffusion system was constructed. A range of nominal gaseous concentrations could be achieved using this system (Fig. 1). The system comprised of two air streams, which were dried by CaSO4 and purified by charcoal filtration and regulated by mass flow controllers (0.5 5 L min−1, MKS Instruments, USA). One of the air streams was passed through a temperature-controlled (585 °C, with an accuracy of ±0.1°C) monoterpene diffusion system, while the other acted as a bypass. The diffusion system had a glass chamber (∼100 mL) housing a sealed vial (1.5 mL) containing 1020 L of a pure monoterpene standard. The septum of the vial was pierced by a syringe, enabling monoterpene vapor to diffuse out at a constant nominal rate into the air stream. The resultant air stream was subsequently combined with the bypass air stream, and mixed over a length of ∼1 m; thereafter, it was sampled by PTR-MS, and/or adsorbed onto solid adsorbent sample tubes for GC-FID analysis. Monoterpene concentrations in the range of parts per billion by volume to parts per million by volume (10−910−6 volume mixing ratio) were achieved by manipulating the two air flow rates and by controlling the water bath temperature. The common and oxygenated monoterpene standards used in the study including myrcene, camphene, -phellandrene, - and -terpinene, linalool, cineole, thujone, and fenchone of purity 96 99% were obtained commercially. PTR-MS operation The sample air containing variable amounts of monoterpenes was introduced to the PTR-MS drift tube via a ∼1-m-long PFA tubing (outer diameter: 1/8 ) at a flow rate of 711.8 mL min−1. To assess fragmentation patterns, the E/N value of the drift tube was varied from 80 to 170 Td (normal value＝120 Td) by altering both the drift tube voltage and the pressure. Gas sampling and GC analysis To identify and quantify the impurities included in the standard vapors, the samples were periodically collected at
Fig. 1
A schematic diagram of a diffusion system that has been used for preparing the standard atmosphere. CF: Charcoal filter Environ. Control Biol.
TERPENOID REACTIONS WITH H3P＋
a flow rate of 200 mL min−1 via a length of 1/4OD PFA tubing, on the dual bed stainless steel sample tubes (Perkin Elmer) containing Tenax-TA (200 mg) and Carbotrap (100 mg). The sample tubes were pre-conditioned at 280°C for 30 min in a stream of purified helium at 50 mL min−1 and were sealed and stored at 4°C until sampling. Impurities in the standard vapors were identified by GC-MS (Hewlett Packard 5890 GC - 5870 MS) and quantified by GC-FID (Perkin Elmer Autosystem). In both these systems, samples underwent two stages of thermal desorption (Perkin Elmer ATD 400). The compound separation was achieved using an Ultra-2 capillary column (Hewlett Packard). GC analytical procedures and parameters are described in detail elsewhere (Hayward et al., 2001). The detection limit (S/N＝3) of the GC-FID system is 0.03 0.04 pmol on the column. Identification of ions derived from standards and impurities A monoterpene concentration of 100 300 ppbv in the gas phase was produced, and the PTR-MS instrument was operated in the scan mode to select all the produced ions in the mass range of 21 200 (including ions derived from any impurities present). Only the ions of which the signals exceeding 0.1% of the signal of the dominant ion were selected, and in the subsequent experiments, the PTR-MS instrument was tuned only to detect them. The ions originated from impurities in the standards were identified using three complementary methods: GCMS/FID analysis of diluted standard vapors and solutions; correlation analysis between individual ions measured by PTR-MS at various concentrations of standard vapors (obtained by varying the water bath temperature); and PTRMS measurements at increased and decreased E/N values in the drift tube (i.e., the varying compound fragmentation). Determination of reaction rate constant The reaction rate constants of some of the target compounds with H3O＋ ions at normal PTR-MS operating conditions were determined from Eqn. 1. The concentration of the neutral [R] was simultaneously measured by GC-FID. Previously determined reaction time t of 101×10−6 s (Tani et al., 2003) was used in the present study. As a reference compound, toluene was used because its rate constant with H3O＋ (2.2×10−9 cm3 s−1) has already determined and the measurement of toluene by PTR-MS has been well characterised and documented (e.g. Warneke et al., 2001). To measure the concentrations of the monoterpene families and toluene by GC-FID and also to calculate the proton transfer reaction rate constant of monoterpene families, we collected 7 to 12 samples of each compound at different vapor concentrations (5 500 ppbv). This was achieved by changing the water bath temperature and/or the flow rates of the diffusion system. Because of the “sticky” nature of these vapors, they were not sampled until their signal measured by PTR-MS reached a steady state. The concentrations determined by GC-FID were plotted against the ion count rates measured by PTR-MS, and the slopes were compared with that of toluene. Since the ratio of the slope of the individual compounds to that of toluene is proportional to the ratio of the rate constant of the compounds Vol. 51, No. 1 (2013)
to that of toluene, the reaction rate constant k for each compound can be calculated. For more detailed description, see our previous paper (Tani et al., 2003) RESULTS
Effect of E/N on fragment pattern of monoterpenes, monoterpene alcohols and monoterpene ketones Several impurities in the standard solutions and their vapors were identified by GC-MS. C10-alkylbenzenes and other monoterpene species were the dominant impurities in these standard solutions. The total GC-FID peak area of the impurities in the vapors was less than 5% in all the cases. Varying the water bath temperature was an effective technique to distinguish the fragment ions derived from the standards and those originating from the impurities, (see Tani et al., 2003). Since the vapor pressure varies as a function of temperature and the functions differ among compounds, fragment ions derived from standards should increase proportionally to their protonated molecular ion as temperature is increased. As a result, they are distinguishable from the impurities. Signals of the ions derived from 13C mono-substituted molecules must also be considered when calculating the VOC concentrations by PTR-MS. Each ion signal is expressed as a percentage of the total signal of all the ions derived from both the non-isotopic and the 13 C monosubstituted molecules of the target compounds (Table 1). All the 5 monoterpenes were measured by PTR-MS using the above technique (camphene, myrcene, -phellandrene, - and -terpinene) and were found to produce fragment ions of m/z 67, 81, and 95, as non-isotopic ions (nonisotopic ions are those that only contain 12C and 1H and not 13 C or 2H). The ion signal of m/z 67 accounted for less than 1.2% of the total ion signal for all the monoterpenes at normal experimental conditions. Ion signal of m/z 95 was also less than 2% of the total ion signal, except in the case of myrcene (8.2%). The protonated molecular ion (m/z 137) at normal conditions was 50 56% for all the 5 monoterpenes measured in the present study. Among the 5 monoterpenes, only myrcene produced an additional fragment ion of m/z 69. The relative abundance of m/z 69 in myrcene was 3.1%. However, as the E/N value of the drift tube was decreased, there is a steady increase in the percentage of m/z 137 (Fig. 2). For each of the monoterpene, the percentage of m/z 137 reached to 80 87% at an E/N value of 80 Td. The percentage of fragment ions steadily decreased with a decrease in E/N value because of the softer collisional reaction between H3O＋ and the monoterpenes. It was observed that the monoterpene alcohols linalool and cineole (m.w.＝154) also produced fragment ions m/z 69, 81, 95, and 137 at 120122 Td (Table 2). The relative abundance of protonated molecular ion m/z 155 was 5.8% and 0.4% for linalool and cineole, respectively. The value increased significantly for cineole as the drift tube E/N value was decreased, but remained low for linalool ( )
A. TANI Table 1
Relative abundance of monoterpene fragment ions and proton transfer reaction rate constant, k, determined by PTR-MS under normal operating conditions (E/N＝120122 Td).
Myrcene Camphene -Phellandrene -Terpinene -Terpinene
67
69
81
95
137
81＋137
Other ions
k (10−9 cm3s−1)
1.0 1.2 0.4 0.4 0.5
3.1
30.7 33.7 38.8 33.9 38.6
8.2 1.1 1.1 0.8 0.8
49.6 55.6 51.3 56.4 51.8
80.3 89.3 90.1 90.3 90.4
70, 82, 96, 138, 155 82, 138 82, 138 82, 138 82, 138, 155
2.4 2.2 2.3 2.3 ―
40.9 37.1 39.6 39.6 31.6
1.3 2.0 1.5 4.7 1.1
49.2 52.4 50.3 47.3 58.2
90.1 89.5 89.8 86.9 89.7
82, 138 82, 138, 155 82, 138 82, 138, 155 82, 138, 155
2.2 ― 2.3 2.3 2.2
(Comparison data from Tani et al. (2003)) -Pinene 0.6 Sabinene 0.5 -Pinene 0.5 Limonene 0.5 3-Carene 0.6
Fig. 2
throughout the E/N range. Further, m/z 137 became dominant (∼75%) at the lowest E/N value of 80 Td (Fig. 2). A monoterpene ketone, thujone (m.w.＝152), produced fragment ions m/z 91, 93, 95, and 135 and a monohydrated ion m/z 171 (C10H14O · H＋ · H2O), in addition to m/z 153, at 120 122 Td (Table 2). Fragment patterns of thujone was also observed to be dependent on the collisional energy value, i.e., E/N. We found that m/z 135 ( )
Fragment patterns of ions (shown as a percentage of total ion signal) derived from myrcene, camphene, cineole, linalool and thujone affected by different values of E/N. Each data point is the mean of 10 20 determinations.
ion was most abundant at E/N values of 100120 Td, but below 100 Td, the protonated molecular ion m/z 153 was dominant (Fig. 2). On the other hand, the other monoterpene ketone, fenchone, was observed to produce no fragment ions. It mostly produced molecular ions and small amount (＜1%) of the monohydrated molecular ion m/z 171.
Environ. Control Biol.
TERPENOID REACTIONS WITH H3P＋ Table 2 Relative abundance of oxygenated monoterpene fragment ions and proton transfer reaction rate constant, k, determined by PTR-MS under normal operating conditions (E/N＝120122 Td). 69 (Monoterpene alcohol) Linalool 3.9 Cineole 0.5 -Terpineol 0.4 91
81
95
137
155
81＋137
Other ions
k (10−9 cm3 s−1)
36.7 35.7 39.3
0.7 0.9 2.2
44.2 54.7 48.7
5.8 0.4 1.5
80.9 90.4 88.0
82, 138, 156, 173 82, 138, 173 82, 138, 173
2.6 3.5 ―
93
95
135
153
171
Other ions
k (10−9 cm3 s−1)
4.6
69.5
0.0 90.1
0.1
136, 154 154, 171
― 3.5
154, 171
4.4
(Monoterpene ketone) Thujone 0.5 17.6 Fenchone (Comparison data from Tani et al. (2003)) Camphor
89.9
DISCUSSION
Fig. 3
Relationship between the concentrations of monoterpenes and oxygenated monotrpenes measured using GC-FID and the total signal of all ions derived from them. The count rate was standardized to 1×106 cps of H3O＋ for toluene and 1×106 cps for H3O＋ plus H3O＋ H2O for the monoterpenes, at 2.0 mbar of the drift tube pressure. The linear regression for each data set were: Camphene, y＝0.0943x, r2 ＝0.9992, n＝8; Myrcene, y＝0.0792x, r2 ＝0.9968, n＝8; Cineole, y＝0.0574x, r2 ＝0.9968, n＝8; Linalool, y＝0.0811x, r2 ＝0.9962, n＝5; Fenchone, y＝0.0549x, r2 ＝0.9963, n＝5; Toluene, y＝0.0912×x, r2＝1.000, n＝11.
Reaction rate constant calculation Figure 3 shows the good linear relationship (r2＝0.98 1.00 for n＝512) between the concentrations of camphene, myrcene, cineole, linalool, and fenchone (measured with GC-FID) and the sum of the signals of all the ions derived from these individual compounds (including 13 C monosubstituted molecules) that were simultaneously measured by PTR-MS. The signals were shown as standardized count per second (SCPS), i.e., standardized to 1 ×106 cps of the proton donors and 2.0 mbar of the drift tube pressure (Tani et al., 2004), because small differences in these values occurred between individual experiments. The rate constant k for monoterpene species (myrcene, camphene, -phellandrene, and -terpinene) was experimentally determined to be in the range 2.2 2.4×10−9 cm3 −1 s (Table 1). The monoterpene alcohols, linalool and cineole, have a higher rate constant of 2.6×10−9 and 3.5 ×10−9 cm3 s−1 , respectively (Table 2). A monoterpene ketone, fenchone, also has been observed to have a high rate constant (3.5×10−9 cm3 s−1).
Vol. 51, No. 1 (2013)
In our previous papers (Tani et al., 2003; 2004), we investigated the fragment patterns of the major monoterpenes, - and -pinene, sabinene, 3-carene, and limonene in detail and showed that they produced fragment ions of m/z 67, 81, and 95. We found that relative abundances of the fragment ions of these 5 monoterpene species were not the same and that they also varied with the E/N values. Following these reports, the fragment patterns of several monoterpenes (Steeghs et al., 2007; Misztal et al., 2012), oxygenated monoterpenes (Maleknia et al., 2007), and sesquiterpenes (Demarcke et al., 2009) have subsequently been reported. The fragment ions of the 5 monoterpenes (myrcene, camphene, -phellandrene, - and -terpinene) and 2 monoterpene alcohols (lionalool and cineole) used in the present study were also addressed (Steeghs et al., 2007), and the major fragment ions (m/z 81 and 95) found in our study were also reported by the authors. However, we found that myrcene exclusively produces a fragment ion m/z 69. Myrcene is the only straightchained compound among all the monoterpenes, and it seems to produce a fragment ion C5H＋9 when the 4 and 5 positions of the carbon-carbon bond are attacked. The other major monoterpenes are the cyclic monoterpenes and are believed to produce a fragmentary cyclic ion C5H＋7 (m/z 67) (Misztal et al., 2012). The m/z 69 is also a protonated molecular ion of isoprene. Both isoprene and monoterpenes are present in the forest atmosphere and in many cases isoprene concentration is much higher than myrcene. However, when measuring BVOC emitted from monoterpene emitting coniferous trees, of which emission includes a large amount of myrcene, it should be noted that myrcene fragment ion m/z 69 may interfere with isoprene quantification. Fragment patterns of the monoterpene ketones, thujone and fenchone, have not been investigated so far. We have found an obvious contrast between thujone and fenchone: thujone produces several fragment ions, including m/z 93 and 135, but fenchone yields no detectable fragment ions. We previously reported that no fragment ions were produced from the monoterpene ketone, camphor (Tani et al., 2003). Among the 3 monoterpene ketones, only thujone has a three-membered ring that is likely to get ( )
A. TANI
cleaved, and this seems the reason for its fragmentation. Ion of m/z 93 is a protonated molecular ion of toluene, which often has the highest concentration among all nonmethane hydrocarbons in the atmosphere. Ion of m/z 93 is also produced by p-cymene (C10 H14 ), which is emitted by many plant species (Tani et al., 2003). In the present study, we found that m/z 93 ion also originate from thujone, and that these fragment ions derived from two different compounds may interfere in the measurement of toluene. This is particularly important when the measurements are made in a rural atmosphere. Fragment ion of m/z 93 originated from other compounds was also considered for toluene quantification (Ambrose et al., 2010). The reaction rate constant k for the 4 monoterpene species (myrcene, camphene, -phellandrene, -terpinene) has been experimentally determined for the first time and has been found to be in the range of 2.2 2.4×10−9 cm3 −1 −9 s . The rate constant of myrcene (2.4×10 cm3 s−1) was theoretically calculated to be 2.57×10−9 cm3 s−1 (Zhao and Zhang, 2004), which is very similar to that observed in our experimental results. The previously reported rate constants of - and -pinene, limonene, and 3-carene (Tani et al., 2003) were also in this range. From the present study, we estimate that linalool, cineole, and fenchone have high values of proton transfer reaction rate constant compared to that of the most common monoterpenes. We had previously reported a high reaction rate (4.4×10−9 cm3 s−1 ) of another monoterpene ketone, camphor (Tani et al., 2003). This value was also very similar to the theoretical value that was calculated using the dipole moment and the polarisability of camphor. Since oxygenated monoterpenes are polar compounds and thus likely to have higher values of dipole moment, it is reasonable to infer that linalool, cineole, and fenchone should have a higher value of proton transfer reaction rate constant. For the practical application of PTR-MS, the ion count of m/z 81＋137 has been used to determine the total monoterpene concentration (e.g. Mochizuki et al., 2011). This is feasible because the sum of these ion counts remains constant at different water vapor concentrations in the sample air (Tani et al., 2004). The total monoterpene concentration in the field has been calculated from the calibration equation of total concentration of the selected monoterpenes against SCPS of m/z 81＋137. For calibration, two to three compounds of monoterpenes, including -pinene, have been used as standards. The results of the present study suggest that two monoterpene alcohols produce major ions of 81 and 137. If plants emit monoterpenes as well as monoterpene alcohols, they both can generate ions 81 and 137. We have shown in the present study that these two families have a different range of proton transfer reaction rate constant (Tables 1 and 2). The abundance of ions yielded by the proton transfer reaction is not the same when the same concentration of monoterpenes and monoterpene alcohols are individually measured (see Fig. 3). This suggests that a calibration equation determined using the selected monoterpenes may cause a significant error in determining ( )
the total concentration of both monoterpenes and monoterpene alcohols emitted by plants. This is especially noted in cases where the herb plants and trees that emit a large amount of monoterpene alcohols are used for emission measurements. Thus, it is essential to first quantify what compounds are emitted by a target plant using GCMS before directly quantifying the total monoterpene concentration by PTR-MS. By calibrating the standard mixture of major compounds emitted from target forests and trees we can achieve greater precision in measuring the total concentration of monoterpenes and monoterpene alcohols. This research was partially supported by the Ministry of Education, Science, Sports, and Culture, Grant-in-Aid for Scientific Research (B), No. 21310026 and Grant-in-Aid for Scientific Research on Innovative Areas No. 20120005. It was also supported by the Japan Society for the Promotion of the Science, A3 Foresight Program “CarboEastAsia”.
REFERENCES Ambrose, J. L., Haase, K., Russo, R. S., Zhou, Y., White, M. L., Frinak, E. K., Jordan, C., Mayne, H. R., Talbot, R., Sive, B. C. 2010. A comparison of GC-FID and PTR-MS toluene measurements in ambient air under conditions of enhanced monoterpene loading. Atmos. Meas. Tech. 3: 959980. Demarcke, M., Amelynck, C., Schoon, N., Dhooghe, F., van Langenhove, H., Dewulf, J. 2009. Laboratory studies in support of the detection of sesquiterpenes by proton-transferreaction-mass-spectrometry. Int. J. Mass Spectrom. 279: 156 162. Fall, R. 1999. Biogenic emissions of volatile organic compounds from higher plants. In “Reactive Hydrocarbons and the Atmosphere” (ed. by Hewitt C. N.), Academic press, London, p 4397. Fehsenfeld, F., Calvert, J., Goldan, R., Guenther, A. B., Hewitt, C. N., Lamb, B., Liu, S., Trainer, M., Westberg, H., Zimmerman, P. 1992. Emissions of volatile organic compounds from vegetation and the implications for atmospheric chemistry : Natural sources of acid precursors, neutralizing compounds, and oxidants. Global Biochemical Cycles 6: 389 430. Hayward, S., Muncey, R. J., James, A. E., Halsall, C. J., Hewitt, C. N. 2001. Monoterpene emissions from soil in a Sitka spruce forest. Atmos. Environ. 35: 40814087. Hewitt, C. N., Hayward, S., Tani, A. 2003. The application of proton transfer reaction-mass spectrometry (PTR-MS) to the monitoring and analysis of volatile organic compounds in the atmosphere. J. Environ. Monit. 5: 1 7. Karl, T., Guenther, A., Jordan, A., Fall, R., Lindinger, W. 2001. Eddy covariance measurement of biogenic oxygenated VOC emissions from hay harvesting. Atmos. Environ. 35: 491495. Karl, T., Harley, P., Emmons, L., Thornton, B., Guenther, A., Basu, C., Turnipseed, A., Jardine, K. 2010. Efficient atmospheric cleansing of oxidized organic trace gases by vegetation. Science 330: 816819. Lindinger, W., Hansel, A., Jordan, A. 1998. On-line monitoring of volatile organic compounds at pptv levels by means of proton-transfer-reaction mass spectrometry (PTR-MS)―Medical applications, food control and environmental research. Int. J. Mass Spectrom. 173: 191241. Maleknia, S. D., Bell, T. L., Adams, M. A. 2007. PTR-MS analysis of reference and plant-emitted volatile organic Environ. Control Biol.
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compounds. Int. J. Mass Spectrom. 262: 203 210. Misztal, P. K., Heal, M. R., Nemitz, E., Cape, J. N. 2012. Development of PTR-MS selectivity for structural isomers: Monoterpenes as a case study. Int. J. Mass Spectrom. 310: 10 19. Miyama, T., Okumura, M., Kominami, Y., Yoshimura, K., Ataka, M., Tani, A. 2012. Nocturnal isoprene emission from mature trees and diurnal acceleration of isoprene oxidation rates near Quercus serrata Thunb. leaves. J. Forest Res. DOI: 10.1007/s10310-012-0350-5. Miyazaki, Y., Fu, P. Q., Kawamura, K., Mizoguchi, Y., Yamanoi, K. 2012. Seasonal variations of stable carbon isotopic composition and biogenic tracer compounds of water-soluble organic aerosols in a deciduous forest. Atmos. Chem. Phys. 121367 1376. Mochizuki, T., Endo, Y., Matsunaga, S., Chang, J., Ge, Y., Haung, C., Tani, A. 2011. Factors affecting monoterpene emission from Chamaecyparis obtusa. Geochem. J. 45: e15e22. Nelson, R. D., Jr. Lide, DR, Jr., Maryott, A. A. 1967. Selected values of electric dipole moments for molecules in the gas phase. Nationals Standard Reference Data Series 10, National Bureau of Standards, Washington DC, pp 49. Okumura, M., Tani, A., Tohno, S., Shimomachi, A. 2008. Lightdependent monoterpene emissions from an oak species native to Asia. Environ. Control Biol. 46: 257 265. Steeghs, M. M. L., Crespo, E., Harren, F. J. M. 2007. Collision induced dissociation study of 10 monoterpenes for identification in trace gas measurements using the newly developed proton-transfer reaction ion trap mass spectrometer. Int. J. Mass Spectrom. 263: 204 212. Su, T., Chesnavich, W. J. 1982. Parametrization of the ion-polar molecule collision rate constant by trajectory calculations. J. Chemical Physics 76: 5183 5185.
Vol. 51, No. 1 (2013)
Tani, A., Hayward, S., Hewitt, C. N. 2003. Measurement of monoterpenes and related compounds by proton transfer reaction - mass spectrometry (PTR-MS). Int. J. Mass Spectrom. 223224: 561 578. Tani, A., Hayward, S., Hansel, A., Hewitt, C. N. 2004. Effect of water vapour pressure on monoterpene measurements using proton transfer reaction - mass spectrometry (PTR-MS). Int. J. Mass Spectrom. 239: 161 169. Tani, A., Kato, S., Kajii, Y., Wilkinson, M., Owen, S., Hewitt, N. 2007. A proton transfer reaction mass spectrometry based system for determining plant uptake of volatile organic compounds. Atmos. Environ. 41: 1736 1746. Tani, A., Kawawata, Y. 2008. Isoprene emission from native deciduous Quercus spp. in Japan. Atmos. Environ. 42: 4540 4550. Tani, A., Hewitt, V. N. 2009. Uptake of aldehydes and ketones at typical indoor concentrations by houseplants. Environ. Sci. Technol. 43: 8338 8343. Tani, A., Bobe, S., Shimizu, S. 2010. Uptake of methacrolein and methyl vinyl ketone by tree saplings and implications for forest atmosphere. Environ. Sci. Technol. 44: 7096 7101. Tani, A., Tozaki, D., Okumura, M., Nozoe, S., Hirano, T. 2011. Effect of drought stress on isoprene emission from two major Quercus species native to East Asia. Atmos. Environ. 45: 62616266. Warneke, C., van der Veen, C., Luxembourg, S., de Gouw, J. A., Kok, A. 2001. Measurements of benzene and toluene in ambient air using proton-transfer-reaction mass spectrometry: calibration, humidity dependence, and field intercomparison. Int. J. Mass Spectrom. 207: 167182. Zhao, J., Zhang, R. 2004. Proton transfer reaction rate constants between hydronium ion (H3 O＋ ) and volatile organic compounds. Atmos. Environ. 38: 2177 2185.
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