Article pubs.acs.org/ac
Simple Pretreatment Procedure Combined with Gas Chromatography/Multiphoton Ionization/Mass Spectrometry for the Analysis of Dioxins in Soil Samples Obtained after the To̅ hoku Earthquake Yu-Ching Chang† and Totaro Imasaka*,†,§ †
Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan § Division of Translational Research, Center for Future Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan S Supporting Information *
ABSTRACT: A simple pretreatment procedure was developed for the analysis of dioxins in soil samples using gas chromatography/multiphoton ionization/time-of-flight mass spectrometry. The sample was subjected to a pressurized liquid extraction procedure, followed by separation using a pair of Sulfoxide and Ag-ION columns for cleanup. Due to the high selectivity of laser ionization, the procedure was simplified and the time required for an analysis was decreased to 3 h. The sample collected after the earthquake and tsunami contained relatively high concentrations of PCBs and PCDD/Fs. This simple and rapid pretreatment procedure can be useful for monitoring the environment to prevent unexpected exposure of toxic dioxins for the workers who have to process more than 20 million tons of the wastes in a few years.
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additional hazardous substances, including dioxins. Therefore, a method for the rapid analysis of such pollutants is urgently required for the safe processing of the hazardous substances. Since PCDD/Fs and PCBs are present in soil, sludge, and waste materials at trace levels and are highly toxic, a sensitive and selective method for their analysis is needed. Gas chromatography combined with high-resolution mass spectrometry (GC/HRMS) or quadrupole mass spectrometry (GC/QMS) is the protocol of choice and is currently used by the Ministry of Environment, Government of Japan.2 However, the electron ionization (EI) employed in these techniques simultaneously ionizes a wide variety of organic compounds including aliphatic and aromatic hydrocarbons, requiring more careful pretreatment before instrumental analysis. The use of laser multiphoton ionization (MPI) reduces the ions arising from interfering compounds with no absorption band at the laser wavelengths.3,4 Several studies have reported that an ultraviolet femtosecond laser (266 nm) can be used as an ionization source and that it can be combined with a
ioxins, which consist of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated furans (PCDFs), and coplanar-polychlorinated biphenyls (coplanar-PCBs), are suspected of having teratogenicity and immunological/endocrine effects in humans.1 Because they are highly stable compounds, their half-lives in the human body are estimated to be 7−11 years. Dioxins are produced by industrial and agricultural activities, in addition to accidental processes, such as oil spills and subsequent conflagrations. After the earthquake and tsunami in the To̅hoku area on March 2011, many oil spills from fishing boats and even from petroleum refineries occurred, which was followed by large-scale conflagrations. As a result, a variety of chemicals that are classified as respiratory hazards, neurotoxins, and carcinogens were released into the environment. Some of these are persistent and pose a potentially increased hazard to life on earth. It should be noted that the facilities where old electric devices containing PCBs were stored were washed away by the disaster and approximately 20 million tons of waste materials, including plastics and products containing polyvinyl chloride, had been accumulated in the waste facility under condition of solarization for a long period of time. Such a high temperature and humidity would provide sufficient energy for chemical reactions to occur, resulting in the production of © 2012 American Chemical Society
Received: October 4, 2012 Accepted: December 3, 2012 Published: December 3, 2012 349
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standard solution. The cleanup spike (PDF-SA-A50) and the syringe spike (PDF-CL-A20) used in this study were supplied by Kanto Chemical Co. Pretreatment Procedure. A soil sample (10 g) was mixed with anhydrous sodium sulfate (Wako Pure Chemical Industries, 30 g) to remove the moisture. The sodium sulfate was heated at 120 °C for 10 h prior to use. The mixture of soil and sodium sulfate was packed in a stainless steel vessel (66 mL, Dionex, Sunnyvale, CA) for PLE (Dionex, ASE 300). For safety assurance, nontoxic 13C-labeled standard solution containing 13C-labeled-1,2,3,4-TeCDD, 13C-labeled-1,2,3,4TeCDF, and 13C-labeled-3,3′4,5′-TeCB (#79) was added as cleanup spikes. The extraction conditions were as follows: extraction temperature, 160 °C; heating time, 8 min; static time, 20 min; purge time, 150 s; flush volume, 50%; extraction cycle, 2; extraction solvent, toluene. Using this protocol, the overall time for the extraction was ca. 1 h. The crude extract was then concentrated with use of a rotary evaporator (NE1001VD, Tokyo Rikakikai Co., Japan), and the solution was further concentrated to 100−200 μL under a stream of nitrogen. The concentrated solution was passed through a Sulfoxide column, and then a Ag-ION column. Solvents such as hexane (elution volume, 0−6.5 mL) and 5% dichloromethane/ hexane (elution volume, >6.5 mL) were used. The Sulfoxide and Ag-ION columns were conditioned independently with use of 10 mL of acetone to remove the moisture and the column was equilibrated with 20 mL of hexane before use. The eluent collected after an elution volume of 6.5 mL was concentrated in a rotary evaporator. After changing the solvent to nonane, the volume of the sample solution was reduced to 20 μL. A syringe spike was added to the solution for calibration of the instrument. GC/MPI/TOFMS. The TOF-MS instrument developed in our laboratory has been reported in detail elsewhere3,10 and is now commercially available (HGK-1, Hikari-GK, Fukuoka, Japan). An aliquot of the sample was injected into a GC system (6890GC, Agilent Technologies, CA) with use of an auto sampler (6890N, Agilent Technologies). The conditions used for the GC separation are summarized in Comment S-1 of the Supporting Information. The analyte molecules were ionized by the third harmonic emission of a femtosecond Ti:sapphire laser (266 nm, 1 kHz, 100 fs, 100 μJ, Libra, Coherent Inc., CA). The ions induced were detected by an assembly of microchannel plates (MCP, F4655-11, Hamamatsu, Shizuoka, Japan). Sampling. The soil samples were collected on July 2011 (4 months after the earthquake) in the To̅hoku areas which had been heavily damaged by the earthquake and tsunami. Seven soil samples (A1−A7) were collected from different locations: samples A1−A3 were from Sendai City, A4 from Shiogama City, A5 and A6 from Kesennuma City, and A7 from Ishinomaki City. A geographic map of the locations is shown in Figure S-1 of the Supporting Information. The procedure used for the sampling is described in Comment S-2 of the Supporting Information. Safety Assurance. Dioxins are extremely toxic compounds, and special care must be taken in handling them and performing experiments with them. The in-house laboratory rules for handling dioxins are listed in Comment S-3 of the Supporting Information. In the reported technology, all toxic dioxins are added as cleanup spikes at the beginning of the pretreatment procedure, and two nontoxic dioxins are mixed as syringe spikes with the sample solution prior to GC analysis. According to the manual established by the Ministry of the
time-of-flight mass spectrometer (TOF-MS) for the sensitive and selective determination of PCDD/Fs.5 In fact, these molecules have been measured at the femtogram level by using GC/MPI/TOF-MS. Due to the improved selectivity in the laser ionization process, it would be possible to simplify the pretreatment procedure. Pressurized liquid extraction (PLE) has been utilized for the extraction of the organic compounds such as organochlorine pesticides, organophosphate pesticides, polycyclic aromatic hydrocarbons (PAHs), PCBs, and PCDD/Fs.6 Because of the higher temperature and pressure used in this type of extraction, compared to Soxhlet extraction, the PLE technique reduces not only the volume of organic solvent needed but also the extraction time. However, the subsequent column separation is a tedious and time-consuming process. A Sulfoxide-bonded silica (Sulfoxide) column was recently developed for use in the analysis of PCBs contained in the mineral oils used in the capacitors and transformers.7 A AgION column developed for separating trans- and cis-isomers of fats based on differences in accessibility has been combined with a Sulfoxide column in series and provides a more complete separation of PCBs.8 In fact, the stationary phase of the AgION column retains PAHs but allows PCBs to be eluted. It should be noted that numerous samples can be processed in parallel since a pair of Sulfoxide/Ag-ION columns require no additional equipments for separation. However, this approach has not yet been applied to the separation of PCDD/Fs.8 In this study, we report on the extraction of PCDD/Fs and PCBs from soil samples using PLE, followed by their separation on a Sulfoxide/Ag-ION column as a cleanup procedure. The sample solution was then analyzed by using a GC/MPI/ TOFMS setup, equipped with an ultraviolet femtosecond Ti:sapphire laser. Dioxins were identified and quantified based on the data from a two-dimensional display. The recovery of the toxic PCDD/Fs and PCBs was determined by using a certified dioxin reference material. Finally, seven soil samples that were collected in the To̅hoku area after the earthquake and tsunami were measured to demonstrate the efficiency and reliability of this method.
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EXPERIMENTAL SECTION Regents. A certified reference material (JASC0422) was supplied from the Japan Society for Analytical Chemistry. The total TEQ has been reported to be 111.4 ± 9.6 pg/g.9 The solvents used for eluting the analytes from the Sulfoxide/AgION column were acetone, dichloromethane, hexane, and toluene, all of which were purchased from Kanto Chemical Co. (Tokyo, Japan) and Wako Pure Chemical Industries (Tokyo, Japan). The sorbents such as activated carbon, Celite, and Na2SO4 were obtained from Wako Pure Chemical Industries. A Sulfoxide column (3 g/6 mL; Cat. No. 55253-U) and a Ag-ION column (750 mg/6 mL; Cat. No. 54225-U) were supplied from Sigma-Aldrich Co. (Tokyo, Japan). A solution containing 16 PCDFs (Wellington Laboratories, Guelph, Ontario, Canada) was used to investigate the elution volume. A standard solution (PDF-CAL-A, CS4-A, Kanto Chemical Co.) containing 17 toxic PCDD/Fs, their corresponding 13C-labed isotopes, and 10 nontoxic PCDD/Fs (including 4 nontoxic 13C-labled isotopes) was measured for the assignment of the signal peaks in GC/ MPI/TOF-MS. The concentration was 10 pg/μL for tetra- and pentaCDD/Fs, 20 pg/μL for hexa- and heptaCDD/Fs, and 50 pg/μL for octaCDD/Fs. The analytical GC/MPI/TOFMS setup was calibrated each day with use of the above-mentioned 350
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elution volumes for m- and p-dichlorobenzenes, suggesting that the retaining force depends on the contact area with the functional groups in the analyte molecule and those in the stationary phase of the Sulfoxide column. It should be noticed that the elution volume for 1,2,3,4-TeCDF was identical with that of 13C-1,2,3,4-TeCDF, indicating that recovery can be accurately measured by using the compounds substituted with 13 C-isotopes. Recoveries. The contents of PCDD/Fs and PCBs in the standard soil sample, i.e., a certified reference material (JSAC0422), were measured to determine the recoveries in the pretreatment process for dioxins. Two-dimensional displays obtained by using Methods A and B are shown in Figure 1, parts A and B, respectively. Most dioxins are separated by GC, and a series of these isotopes can be determined by mass spectrometry. The concentrations and recoveries calculated from the data shown in Figure 1 are listed in Table S-1 of the Supporting Information. Although the contaminants in the standard soil sample were removed more efficiently by using
Environment, Government of Japan, the acceptable range for the cleanup spike is 0.4−2 ng, which is higher than the upper limit adopted in the laboratory rule (0.280 ng-TEQ/day). For this reason, three nontoxic dioxins, i.e., 13C-1,2,3,4-TeCDD/F and 13C-3,3′,4,5′-TeCB (#79), which were currently used as syringe spikes, were used as cleanup spikes. On the other hand, the standard solution containing all the toxic dioxins currently used as cleanup spikes was employed as syringe spikes in this study. This approach would be useful for retaining safety assurance, although the concentration cannot be calibrated against the isotopes of toxic dioxins. The TEQ could be more accurately determined by using a larger amount of toxic dioxins in a laboratory that is specially designed for handling toxic compounds such as these.
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RESULTS AND DISCUSSION Elution Volume. In a previous study, a pair of Sulfoxide/ Ag-ION columns was used to separate PCBs contained in mineral oil, and all of the toxic PCBs were collected in an elution volume of 8−20 mL.11 No data concerning the elution volume of PCCD/Fs have been reported to date. The elution volume was investigated for a sample containing 2,3,4,7,8PeCDF, 1,2,3,4,6,8-HxCDF, 1,2,3,4,6,7,8-HpCDF, and OcCDF with the Sulfoxide column. In this preliminary study, the AgION column was connected to a Sulfoxide column after 6.5 mL had been eluted, according to the protocol provided by the manufacturer for the analysis of PCBs (Method A).11 The eluent was collected at volumes of 4.5, 6.5, and 18.5 mL, and thereafter every 2 mL was collected up to 26.5 mL. The concentration of the analyte decreased drastically after an elution volume of 6.5 mL, suggesting that the PCDFs were largely eluted from the Sulfoxide column at this stage. For the analysis of PCBs in insulating oils, the major components of the mineral oil and aromatic hydrocarbons with no chlorine atoms would degrade the cleanup capability of the Ag-ION column. To eliminate this, the column was connected after the elution volume of 6.5 mL. However, a sample extracted from soil does not contain high concentrations of these organic compounds. Therefore, we investigated an approach where these two columns were connected in series from the beginning of the separation stage (Method B). A sample solution containing 16 congeners of PCDFs was injected into a Sulfoxide column connected to a Ag-ION column in series, and the columns were then eluted with toluene, acetone, or hexane. Samples were collected every 2 mL (2.5 mL for the first eluent), and the concentration was measured, as shown in Figure S-2 of the Supporting Information. The Sulfoxide and Ag-ION columns developed a color when toluene was used as the eluent, as shown in Figure S-3 of the Supporting Information. This color change indicates that the performance of the column had deteriorated. It has been reported that the stationary phase of the Ag-ION column retains compounds having cis-double bonds.12 All PCDFs with aromatic rings (i.e., with cis-double bonds) were, however, eluted at an early stage, similar to the elution time for the case of mineral oil. When acetone was used as an eluent, the majority of the PCDFs were eluted at the same time, suggesting that a polar solvent is not suitable for retaining PCDFs. On the other hand, when hexane, a nonpolar solvent, was used, all of the PCDFs were eluted in a volume of 6.5−20 mL. The elution volume would change depending on the number and positions of the substituents in the PCDFs. For example, the elution volume for o-dichlorobenzene is reported to be larger than the
Figure 1. Two-dimensional displays for a standard soil sample measured by using GC/MPI/TOFMS: (A) the Ag-ION column was combined with a Sulfoxide column after 6.5 min of elution time (Method A) and (B) the Ag-ION column was combined with a Sulfoxide column from the beginning of the separation (Method B). 351
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Method A, the recoveries were 10−53%, lower than the recoveries (50−120%) required by the Ministry of the Environment, Government of Japan.2 On the other hand, the recoveries of PCDD/Fs and PCBs were 51−133% for Method B, although the contaminants were relatively increased. The variation in the recoveries can be attributed to the use of nontoxic internal standards, instead of toxic 13C-isotopes, as cleanup spikes for safety assurance (cf. Experimental Section). The total TEQ calculated was 53% of the certified value. The relatively lower values can be attributed to the fact that the signal peak for one of the most toxic compounds, 1,2,3,7,8PeCDD, was covered by a signal arising from contaminants and was neglected in this study. These components could be separated by using a different GC column, suggesting that using two types of GC columns for the complete separation of dioxins, but sometimes using only a single GC column can reduce analysis time at the expense of accuracy. Soil Samples in the To̅hoku Area. Seven soil samples (A1−A7) were collected from the To̅hoku area after the earthquake and tsunami and were extracted following the protocol proposed in Method B. The data for the soil sample derived at location A3 are shown in Figure 2, suggesting that no
Figure 3. Two-dimensional display of the sample obtained at location A4. The sample solution was diluted 5 times to avoid saturation of the signals. The expanded view of the portion corresponding to 3,3′,4,4′,5PeCB (#126) is shown as an insert in the figure. A series of isotope peaks were observed and were used for quantification, although the signal is partly obscured by a large signal arising from a contaminant.
mass spectrometry. The presence of PCDD/Fs and PCBs can be confirmed from the intensity distribution of the isotope peaks. Some PCDD/Fs were not clearly measured because their signals were obscured by overlapping signals arising from PCBs. The pretreatment procedure used in this study is based on the separation of chlorinated aromatic hydrocarbons from aliphatic and aromatic hydrocarbons with no chlorine atoms, and it is difficult to quantify PCDD/Fs when a large amount of PCBs with similar properties with respect to the retention time in GC and the m/z value in MS are present in the sample. Then, it would be necessary to further investigate the eluting conditions for column separation to solve this problem. Assuming that the ionization efficiency of 12C-native-PCB is identical with that of 13C-labled isotopes (this assumption has been confirmed to be valid for PCDD/Fs),5 the concentrations of the native-PCBs can be calculated by measuring the relative intensities of the signals against the signals corresponding to the isotopically labeled compounds. The results are summarized in Table S-2 of the Supporting Information. The peaks arising from 3,3′,4,4′,5-PeCB (#126) are partly obscured by a large signal of a contaminant probably a nontoxic PCB. However, due to a slight change in retention time, the concentration of #126 could be evaluated and the total TEQ was determined to be 148 pg-TEQ/g. This value is larger than the investigative index for dioxins for a soil sample (>100 pg-TEQ/g),2 and will require further investigation. The Ministry of the Environment investigated soil samples at 78 locations in the To̅hoku area after the earthquake and tsunami. Their study reported a survey result of 0.53 pg-TEQ/g,13 although the area investigated was only 2 km away from our sampling point. Then, the TEQ value is 280 times higher than the reported one. The sampling date was nearly the same (both in July, 2011). The main reason for this would be the difference in the location of the sampling. In fact, sampling point A4 in this study was closer to the waste yard, where a large amount of garbage had been stacked and was left under long-term solarization. It should be noted that facilities storing PCBs were destroyed by the earthquake and tsunami and the PCBs contained in old electric consumables such as transformers and capacitors would be expected to spread. Similarly, two soil samples obtained at locations A1 and
Figure 2. Two-dimensional display of the sample obtained at location A3. A series of components, which are not separated by GC, corresponding to organic compounds such as aromatic and aliphatic hydrocarbons are suspected to be derived from petroleum.
dioxins were present in this area. Similar results were obtained for the samples collected at locations A2 and A5, and the results are shown in Figures S-4 and S-5 of the Supporting Information. Similar two-dimensional displays were obtained for samples containing crude and mineral oils, indicating that the sample contained petroleum. This result can be attributed to oil spills from the oil tanks that were destroyed by the tsunami, cf. even a large ship was transferred to an inner area and was then destroyed by the effect of the tsunami. A two-dimensional display of the sample obtained at location A4 is shown in Figure 3. Since the signal intensities of the PCBs were very large and saturated, several internal standards were covered by the peaks for PCBs that were present at high concentrations. To rectify this, the sample solution was diluted 5 times and mixed with a solution containing the internal standards. Numerous PCBs ranging from TriCBs to NonaCBs were observed. Only 12 isomers of the PCBs are toxic, and they can be assigned by using 13C-labled-PCBs. The isotope peaks for each PCB were separated due to sufficient resolution in 352
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such as dioxin before the start of reconstruction efforts in this area.
A6 were found to contain 2,3′,4,4′,5-PeCB (#118) and 2,3,3′,4,4′-PeCB (#105). Two-dimensional displays of the data for these samples are shown in Figures S-6 and S-7 of the Supporting Information, respectively. Their concentration levels were, however, low and the levels were negligible when compared to the investigative index. A two-dimensional display for a sample derived at location A7 is shown in Figure 4. The concentrations of 29 toxic
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ASSOCIATED CONTENT
S Supporting Information *
Conditions used for the GC column (Comment S-1), the sampling procedure (Comment S-2), the safety assurance in the laboratory (Comment S-3), recoveries for Methods A and B (Table S-1), the concentrations of PCBs and the TEQ for Sample A4 (Table S-2), the concentrations of PCDD/Fs and PCBs and the TEQ for Sample A7 (Table S-3), the sampling locations in the To̅hoku area (Figure S-1), the elution volumes for PCDFs (Figure S-2), the photograph for the Sulfoxide/AgION columns (Figure S-3), the two-dimensional display for Sample A2 (Figure S-4), the two-dimensional display for Sample A5 (Figure S-5), the two-dimensional display for Sample A6 (Figure S-6), and the two-dimensional display for Sample A1 (Figure S-7). This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
Figure 4. Two-dimensional display of the sample obtained at location A7. Numerous peaks arising from PCDD/Fs and PCBs are observed, which would be produced by conflagrations or chemical reactions, resulting in the formation of dioxins in the waste yard.
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ACKNOWLEDGMENTS The authors wish to thank Associate Professor Takeshi Fujita of To̅hoku University for his assistance in sampling, and Dr. Takahiko Matsueda and Dr. Kenji Ohno of Fukuoka Institute of Health and Environmental Sciences for their discussions in this study. This research was supported by a Grant-in-Aid for the Global COE program, “Science for Future Molecular Systems” from the Ministry of Education, Culture, Sports, Science and Technology of Japan and by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS KAKENHI Grant Nos. 23245017 and 24510227). This study was also supported by the Steel Industry Foundation for the Advancement of Environmental Protection Technology.
congeners and their contributions to the TEQ are listed in Table S-3 of the Supporting Information. The TEQ for the sample derived at location A7 was 54 pg-TEQ/g. Before the earthquake and tsunami, the Ministry of the Environment reported a TEQ value of 0.11 pg-TEQ/g at a distance of 4.5 km from the sampling location A7. This difference suggests that the TEQ drastically increased as the result of the earthquake and tsunami. It should be noted that this area was burned in a conflagration. As a result of this, there was a 1-km-long open-air waste and sludge, where numerous destroyed automobiles and waste metals were piled up near the seashore. Because of this, a conflagration would be one of the sources for the detected dioxins, and, therefore, their concentration levels should be carefully investigated before starting any reconstruction of this area, since the concentration would be expected to be higher near the waste yards.
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REFERENCES
(1) WHO, Dioxins and their effects on human health; Fact Sheet N′225, 2010, http://www.who.int/mediacentre/factsheets/fs225/en/. (2) Ministry of Environment, Government of Japan, Manual for the measurement of Dioxins in Soils, 2009, http://www.env.go.jp/chemi/ dioxin/manual/dojo-manual/main.pdf. (3) Hertz, R.; Streibel, T.; Liu, C.; McAdam, K.; Zimmermann, R. Anal. Chim. Acta 2012, 714, 104−113. (4) Cullett, B. K.; Oudejans, L.; Tabor, D.; Touati, A.; Ryan, S. Environ. Sci. Technol. 2012, 46, 923−928. (5) Watanabe-Ezoe, Y.; Li, X.; Imasaka, T.; Uchimura, T.; Imasaka, T. Anal. Chem. 2010, 82, 6519−6525. (6) U.S. EPA, METHOD 3545; PRESSURIZED FLUID EXTRACTION (PFE), 1996, http://www.epa.gov/sam/pdfs/EPA-3545a.pdf. (7) Numata, M.; Aoyagi, Y.; Tsuda, Y.; Yarita, T.; Takatsu, A. Anal. Chem. 2007, 79, 9211−9217. (8) Simple pretreatment procedure for PCB in an insulating oil using Supelclean Sulfoxide and Discovery Ag-ION, Toshiro Kaneko, Technical Report, Nov. 11, 2010, Sigma-Aldrich, Japan. (9) The Japan Society for Analytical Chemistry, Certified reference material JSAC0422, 2008, http://www.jsac.or.jp/srm/srm-n4-2.pdf. (10) Li, A.; Uchimura, T.; Watanabe-Ezoe, Y.; Imasaka, T. Anal. Chem. 2011, 83, 60−66.
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CONCLUSIONS A simple pretreatment procedure, based on a separation using a Sulfoxide/Ag-ION column, was investigated for use in conjunction with GC/MPI/TOF-MS. This procedure removes a major part of the contaminants, which are comprised of aliphatic and aromatic hydrocarbons with no chlorine atoms. Due to superior selectivity in multiphoton ionization, this simple procedure reduced the analysis time for dioxins contained in the soil samples near the waste yard that was prepared after the To̅hoku earthquake and tsunami. In fact, seven soil samples were measured in 3 days, which could be further reduced by using a specially designed laboratory that could safely handle larger amounts of toxic dioxins as internal standards. Since chemical hazards must be evaluated before processing soil and waste samples, and the present approach would have an advantage in terms of evaluating contaminants 353
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(11) Supelclean Sulfoxide Column for pretreatment of PCB in a transformer, Technical Report, Sigma-Aldrich, Japan. (12) Shimelis, O.; Aurand, C.; Trinh, A. Discovery Ag-ION SPE offers sufficient selectivity to fractionate different classes of FAMEs including cis/trans structural isomers, Technical Report, SigmaAldrich, 2006. (13) Ministry of the Environment Government of Japan, Publication about the survey result of the soil environment monitoring in disaster area, 2011, http://www.env.go.jp/jishin/monitoring/result_ gw110819.pdf.
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