Anal. Chem. 2002, 74, 484-487
A Diffusive Badge Sampler for Volatile Organic Compounds in Ambient Air and Determination Using a Thermal Desorption-GC/MS System Noriko Yamamoto,* Tomoko Matsubasa, Nami Kumagai, Sachiko Mori, and Koji Suzuki
Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Kouhoku-ku, Yokohama 223-8522, Japan
A sensitive personal badge sampler packed with Carbopack B for ambient levels of volatile organic compounds and an analytical system using a thermal desorptionpreconcentration-GC/MS have been developed. The capacity of the new sampler was sufficient for an 8-h sampling period, and the analytical method was sensitive enough for the measurement of sub-ppb levels for a 2-h sampling period. The samplers were compared to diffusive samplers (OVM 3500) for typical environmental concentrations. There was a good correlation between the results obtained with the new samplers and the OVM samplers.
Volatile organic compounds (VOCs) in the atmosphere have long been recognized as direct hazards to human health, and diffusive samplers are used to measure personal exposure in the workplace atmosphere. More recently, VOCs have been recognized as a source of indoor air pollution; therefore, it has become necessary to monitor their levels inside buildings and in the ambient air. Passive samplers were ordinarily designed to measure concentrations at ppm levels over an 8-h period in the workplace atmosphere. However, for indoor or ambient applications, their detection limits need to be below 1 ppb for certain target compounds.1-3 Commercially, passive samplers mainly fall into two categories differing in their geometry: badge-type and tubetype devices. Tube-type samplers are characterized by a long axial diffusion path and a low cross-sectional area with relatively low sampling rates.4-6 Badge-type samplers typically have higher sampling rates due to the combination of a shorter diffusion path and greater cross-sectional area compared to the tube-type samplers.7,8 (1) Daisey, J. M.; Hodgson, A. T.; Fisk, W. J.; Mendell, M. J.; Ten Brinke, J. Atmos. Environ. 1994, 28, 3557. (2) Otson, R.; Fellin, P.; Tran, Q. Atmos Environ. 1994, 28, 3563. (3) Yamamoto, N.; Okayasu, H.; Murayama, S.; Mori, S.; Hunahashi, K.; Suzuki, K. Atmos. Environ. 2000, 34, 441. (4) Kilic, N.; Ballantine, J. A. Analyst 1998, 123, 1795. (5) Tolnai, B.; Geleneser, A.; Barko, G.; Hlavay, J. Analyst 1999, 124, 1859. (6) Gelecser, A.; Kiss, Gy.; Hlavay, J.; Hafkenscheid, Th. L.; Peters, J. B.; de Leer, E. W. B. Talanta 1994, 41, 1095. (7) Begerow, J.; Jermann, E.; Keles, T.; Koch, T.; Dunemann, L. J. Chromatogr., A 1996, 749, 181. (8) Fellin, P.; Otson, R. Atmos. Environ. 1994, 28, 1581.
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Two different desorption methods exist for these samplers: thermal and solvent. The solvent desorption procedure has normally been used for VOCs collected on activated carbon as the adsorbent. However, a solvent desorption procedure presents the disadvantage of decreased sensitivity due to the dilution of the desorbed compounds. Thermal desorption has the advantage for analysis with high sensitivity. However, due to the physical constraints of the badge type, the badge-type samplers have recently been incompatible with thermal desorption. Therefore, we developed a new diffusive badge sampler loaded with Carbopack B, a thermally desorbable adsorbent, and a thermal desorption-preconcentraion-GC/MS system using a new thermal desorption device for the sampler. Indoor and outdoor validation studies were carried out on the badge samplers using the analytical system. Simultaneously, active sampling measurements were made by the same analytical system using the preconcentration-GC/MS procedure. In this study, five selected aromatic hydrocarbons (benzene, toluene, ethylbenzene, m-p-xylene, o-xylene) were investigated as the principal VOCs in the indoor and outdoor atmosphere for a 2-8-h sampling period. The new samplers were compared with diffusive samplers (OVM 3500) for typical environmental concentrations.9 There was a good correlation between the results obtained with the samplers and the OVM samplers. This sensitive sampler can be used to measure the VOCs in the atmosphere at sub-ppb levels for a 2-8-h sampling period using the thermal desorption-preconcentrationGC/MS system. EXPERIMENTAL SECTION Standard Samples. Standard samples for the 54 VOCs were prepared by diluting the liquid standard containing a mixture of the 54 VOCs (Tokyo Kasei Kogyo, Japan). Badge Construction. The new diffusive badge-type sampler was designed to have a large exposure area and to be compatible with thermal desorption. As the sampler holder in this study, the OVM 3500 (3M) cartridge was used. The sampler is a badgetype passive sampler consisting of a permeable membrane and an adsorbent disk assembled in a disk-shaped plastic holder. (9) Berow, J.; Jermann, E.; Keles, T.; Dunemann, L. Fresenius J. Anal. Chem. 1999, 363, 399 10.1021/ac010794f CCC: $22.00
© 2002 American Chemical Society Published on Web 12/12/2001
Figure 1. Schematic diagram of the thermal desorption-preconcentration-GC/MS system.
Figure 2. Schematic diagram of the thermal desorption device.
Throughout the exposure, the VOCs were collected through a PTFE filter (Advantec, PTFE, pore size 0.1 µm) and adsorbed onto the adsorbent disk. The cross-sectional area through which diffusion occurs is 7.07 cm2 and the diffusion distance is 1 cm. The new adsorbent disk for thermal desorption was made by packing 50 mg of Carbopack B (60-80 mesh, Supelco) between two glass fiber filters (Advantec, GA-55, pore size 0.6 µm). The glass fiber filters were fixed with 2 M NaOH around the disk and then dried in a vacuum desiccator. The adsorbent disk was preconditioned for 20 min at 250 °C at a flow rate of 50 mL/min with He using a new thermal desorption device connected to the preconcentration-GC/MS system (Figures 1 and 2) and was put in the cartridge and packed in an aluminum bag. After exposure, the samplers were returned to the aluminum bag and stored at -15 °C. Analytical Instrumentation. Figures 1 and 2 show the instrumental arrangements used for the thermal desorption of the adsorbent disk, preconcentration, and GC/MS analyses of the VOCs. After exposure, the adsorbent disk was moved to the thermal desorption device coupled with the preconcentration-GC/MS system. The adsorbent disk was heated and the adsorbed
compounds were desorbed at 250 °C for 20 min at a flow rate of 50 mL/min with the carrier gas. The desorbed compounds were preconcentrated using the multibed collection tube at ambient temperature. The multibed collection tube (0.2 cm i.d. × 15 cm, stainless steel) was packed with a combination of 112 mg of Carbopack B (60-80 mesh, Supelco), 83 mg of Carboxen 1000 (60-80 mesh, Supelco) and 17 mg of Carboxen 1001 (60-80 mesh, Supelco). When the collecting transfer was completed, the valves were switched to the dry purge position and a nitrogen purge was used to remove any water vapor from the sampled air for 4 min at a flow rate of 50 mL/min prior to the thermal desorption. Valve 2 was then turned to the injection mode. Simultaneously, the collection tube was rapidly heated to 280 °C and maintained for 8 min. The trapped compounds were desorbed and introduced into the capillary column by back-flushing with carrier gas at a flow rate of 1 mL/min. At this point, the GC temperature program was automatically started. During the subsequent analysis, the collection tube was refreshed at 280 °C by a nitrogen purge. At the end of the nitrogen purge time, the valves were switched to the sampling mode.10 The GC/MS work was performed using a Shimadzu GC-7A/ MS-QP5050A. Capillary column separation was done using a 3-µmthick film [60 m × 0.25 mm i.d. DB-624 (J&W Scientific)]. The MS was used in the selected ion monitoring mode (SIM). The thermal desorption-preconcentration-GC/MS operating conditions are listed in Table 1. To prevent the adsorption of compounds in the air sample onto the internal surface of the stainless tubes, the tubes were heated with a ribbon heater at 90 °C. For operation of the thermal desorpiotn and analysis, the switching valves, mode of heating, several time sequences, and integrator were regulated by a Shimadzu chromatopack C-R2. The active sampling method was done using the same analytical system with the preconcentration-GC/MS procedure. The air sample was collected by passing it through the multibed collection tube at a flow rate of 50 mL/min for 20 min at ambient (10) Yamamoto, N.; Okayasu, H.; Hiraiwa, T.; Murayama, S.; Maeda, T.; Morita, M.; K. Suzuki. J. Chromatogr., A 1998, 819, 117.
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Table 1. Analytical Conditions of the Thermal Desorption-Preconcentration-GC/MS System Preconcentration-GC/MS GC/MS Shimadzu GC-17A‚MS-QP5050A column DB-624 0.252 mm × 60 m temp program 40 °C (4 min), 8 °C/min, 200 °C(12 min) preconcentrationGAS-30 thermal desorption carrier gas He, 1.0 mL/min collection tube 2.1 mm i.d., 15 cm long (Carbotrap B, 112 mg; Carboxen 1000, 83 mg; Carboxen 1001,17 mg) heating temp 280 °C desorption time 8 min dry purge 50 mL/min, 4 min Thermal Desorption Oven of the Adsorbent Disk heating temp 250 °C carrier gas He, 50 mL/min desorption time 20 min
temperature, and analyses of the sample were made with the same operating conditions as mentioned above. RESULTS AND DISCUSSION The new diffusive badge samplers have been validated for measurements of the five selected VOCs (benzene, toluene, o-, m-, and p-xylenes, ethylbenzene, trichloroethene, tetrachloroethene, 1,4-dichlorobenzene) in outdoor and indoor air. Calibration, Reproducibility, and the Detection Limit. The calibration curves of the five selected VOCs were made by injecting the standard solutions into the collection tube and analyzed under the given experimental conditions. The calibration curves of the five selected VOCs standards were linear over the range of 1-7 ng (regression coefficients of 0.99-1.00). The detection limits (S/N ) 3) of benzene and toluene are 0.1 pg, and the relative standard deviations of the five VOCs were better than 10% for 1 ng of these VOCs Recovery Efficiency. In this study, the new thermal desorption device for the badge sampler was developed for the preconcentration-GC/MS analysis. The thermal desorption device had a rapid temperature rise and was accurate. Thermal desorption of the collected compounds from the adsorbent disk was rapidly performed at 250 °C using the thermal desorption device. Recovery efficiencies for the selected five VOCs from the adsorbent disk were determined with typical environmental concentrations levels by changing the thermal desorption time at 250 °C under the given operating conditions. The recovery efficiencies for all of the five selected compounds were 100%, when the time allotted for the thermal desorption was over 15 min at 250 °C; therefore, a 20-min desorption time was selected for use. Another advantage of the sampler is that the sampler can be more easily preconditioned to remove blanks. Field Application. Field validation studies were carried out using the diffusive badge samplers. The concentrations of the five selected VOCs in the indoor and outdoor atmosphere in Yokohama were calculated from the amount collected by the samplers. Sampling rates of the diffusive sampler for the VOCs were calculated from the results obtained by simultaneous active sampling measurements. The sampling rates of the sampler for 486 Analytical Chemistry, Vol. 74, No. 2, January 15, 2002
Figure 3. Chromatogram of VOCs by the diffusive badge sampler method and active sampling method of the atmosphere of Hiyoshi, Yokohama. Table 2. Comparison of Measured Values by the Diffusive Badge Sampler and Active Sampler Method in the Atmosphere of Hiyoshi, Yokohama, for a 2-h Sampling Period mean ( SD (µg/m3)HR (n ) 3) compounds
diffusive badge sampler
benzene toluene ethylbenzene m-,p-xylene o-xylene styrene a
nda
2.16 ( 0.47 2.09 ( 0.09 2.85 ( 0.06 2.72 ( 0.04
active sampling nd 2.35 ( 1.11 3.07 ( 0.27 2.69 ( 0.05 2.89 ( 0.07
nd, not determined.
the VOCs at ambient levels were available for exposure times up to 8 h. Figure 3 shows typical chromatograms of ambient air samples obtained by the new sampler (a) and active sampling method (b) for a 2-h sampling period in the atmosphere of Hiyoshi, Yokohama. The concentrations of the VOCs measured by the passive sampler were compared to that of the active sampling method, and good agreements were observed between the two independent methods as shown Table 2. The new sampler was compared with the OVM 3500 diffusive sampler for typical environmental concentrations. The results of
Figure 4. Comparison of measured values by the diffusive badge sampler method and OVM 3500 sampler method for a 2-8-h sampling period
simultaneous VOC determinations for a 2-8-h sampling period in the outdoor air with the new samplers and the OVM 3500 are shown in Figure 4. There was a good correlation between the results obtained with the sampler and the OVM 3500. This diffusive badge sampler allows the measurement of low concentrations of VOCs even for short exposure durations using the thermal desorption-preconcentration-GC/MS system. CONCLUSIONS We have described a diffusive badge sampler for measurement of ambient atmospheric levels of VOCs and an analytical system using thermal desorber-GC/MS. The combination of the badge
sampler using a thermal desorbable adsorbent and analysis using a thermal desorber-GC/MS allows measurement of VOCs as low as 0.1 ppb for a 2-8-h sampling period. The method has been successfully validated to be capable of measuring the VOCs at sub-ppb levels in indoor and outdoor air for a 2-8-h exposure period. This sensitive sampler and affordable analytical system using thermal desorber-GC/MS are effective for monitoring ambient levels of VOCs with high sensitivity.. Received for review July 16, 2001. Accepted October 23, 2001. AC010794F
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