Spray Inlet Proton Transfer Reaction Mass Spectrometry (SI-PTR-MS

Feb 11, 2016 - Rapid and sensitive monitoring of benzene in water is very important to the health of people and for environmental protection. A novel ...
0 downloads 0 Views 655KB Size
Download PDF
Subscriber access provided by University of Pennsylvania Libraries

Article

Spray inlet-proton transfer reaction-mass spectrometry for rapid and sensitive on-line monitoring benzene in water Xue Zou, Meng Kang, Aiyue Li, Chengyin Shen, and Yannan Chu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.5b04301 • Publication Date (Web): 11 Feb 2016 Downloaded from http://pubs.acs.org on February 22, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Spray inlet-proton transfer reaction-mass spectrometry for rapid and sensitive on-line monitoring benzene in water Xue Zou, Meng Kang, Ai-Yue Li, Cheng-Yin Shen*, and Yan-Nan Chu Center of Medical Physics and Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China ABSTRACT: Rapid and sensitive monitoring benzene in water is very important to the health of people and the environmental protection. A novel and on-line detection method of spray inlet-proton transfer reaction-mass spectrometry (SI-PTR-MS) was introduced for rapid and sensitive monitoring trace benzene in water. A spraying extraction system was coupled with the selfdeveloped PTR-MS. The benzene was extracted from the water sample in the spraying extraction system, and continuously detected with PTR-MS. The flow of carrier gas and salt concentration in water were optimized to be 50 sccm and 20% (W/V), respectively. The response time and the limit of detection (LOD) of the SI-PTR-MS for detection of benzene in water were 55 s and 0.14 µg/L at 10s integration time, respectively. The repeatability of the SI-PTR-MS was evaluated, and the relative standard deviation (RSD) of five replicate determinations was 4.3%. The SI-PTR-MS system was employed for monitoring benzene in different water matrices, such as tap water, lake water and waste water. The results indicated that the on-line SI-PTR-MS can be used for rapid and sensitive monitoring trace benzene in water.

Benzene is an important industrial chemical used worldwide as chemical intermediate and solvent for production of plastics and polymers.1 Due to the discharge of waste water containing benzene from chemical factories into water environment, benzene has become one of the important factors affecting water quality, as heavy metals and other organic pollutants.2 The effects of exposure to benzene contain changes in the liver and harmful effects on the kidneys, heart, lung and nervous system.3 Therefore, to protect the health of people and the environment, it is essential to measure the benzene in water. And the maximum contaminant level (MCL) of 5 µg/L for benzene in drinking water was established by the US Environmental Protection Agency (EPA),4 and the MCL of 1 µg/L for benzene in drinking water was established by the European Union (EU).5 Conventional solid-phase extraction (SPE) or solid-phase microextraction (SPME) combined with various detecting instruments were commonly used for measurement of benzene in water.1,6-11 Due to time consuming extraction, these techniques cannot be applied for real-time and on-line detection of benzene in water. A permeable membrane combined with photoacoustic sensor had been used for on-line concentration and monitoring of benzene in water.12 However, this method had a very long response time of 40 min, and its limit of detection (LOD) was 350 µg/L, which is much higher than MCL of the US EPA and the EU.4, 5 Baumbach13 developed a membrane inlet ion mobility spectrometers (MI-IMS) technique for

sensitive and on-line monitoring benzene dissolved in water. The LOD of this method for benzene was 1µg/L, just reached to the MCL of the EU.5 And its total analysis time was 90 s. Therefore, there still remains much research effort on developing on-line measurement system for rapid and sensitive detection of benzene in water. Proton transfer reaction mass spectrometry (PTR-MS) allowed real-time measurements of volatile organic compounds (VOCs) with a low LOD and a fast response time.14 This technique has been applied in environmental monitoring, medical research, public security and food inspection.15-18 Therefore, PTR-MS presents a potential for on-line measurement of benzene dissolved in water by extracting benzene from liquid phase to gas phase. Two types of extraction, viz., membrane extraction12, 13, 19-23 and bubbling extraction24-27 were combined with PTR-MS for on-line measurement of VOCs in water. The potential weakness of membrane extraction is the memory effect and long response time.19 The bubbling extraction need much water sample of more than 10 L/min.26, 27 In this study, a spray inlet PTR-MS (SI-PTR-MS) system was introduced for rapid and sensitive monitoring trace benzene dissolved in water. A spraying extraction system was designed for on-line and rapid extraction of benzene in water, and a PTR-MS was used to monitor the extracted benzene. Two important parameters, carrier gas flow and salt concentration in the water, were optimized firstly. And then, LOD and

ACS Paragon Plus Environment

Analytical Chemistry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 6

repeatability of SI-PTR-MS for benzene in water were evaluated. Lastly, the on-line SI-PTR-MS system was applied for monitoring benzene in different water matrices, such as tap water, lake water and waste water. 

EXPERIMENTAL SECTION

PTR-MS instrument. The experiment was performed on our home-made PTR-MS apparatus (Ion Sniffer 2020Q) as described in our previous works,18, 24, 25, 28-30 and detailed information about PTR-MS technique can be found elsewhere.14, 17, 31, 32 Briefly, our PTR-MS instrument consists of a glow discharge ion source, drift tube and quadrupole mass spectrometer (QMS). The reagent ions H3O+ were generated in the ion source through glow discharge with the water vapor, and then injected into the drift tube. When sample gas including benzene vapor was introduced to the drift tube, benzene (C6H6) can undergo proton transfer reaction with H3O+ (Equation 1) as it has a higher proton affinity (PA) value of benzene (PA=750.4 KJ/mol) than H2O (PA=691.0 KJ/mol). H3O++C6H6→C6H6·H++H2O

(1)

After passing through a differentially pumping intermediate chamber, the product ions of benzene (C6H6·H+) and reagent ions (H3O+) at the end of drift tube were introduced into the vacuum chamber and detected by the QMS. The ion peak of protonated benzene at m/z 79 would appeared in mass spectrum according to previous study.24, 25 Ion intensity was given in counts per second (cps). In this experiment, the temperature in the laboratory was maintained to be 20(±1) oC, and the pressure of drift tube was 1.46 Torr. Since too high intensity at m/z 19 (H3O+) and 37 (H3O+·H2O), the mass range of full scan was set to m/z 20-200, except m/z 37. Spraying extraction system. As shown in Figure 1, the spraying extraction system mainly consists of a peristaltic pump (BT360, Yingxiang Science and Technology Ltd., Hebei, China), a sprayer, a teflon atomizing chamber (i.d. 2.5 cm, height 30 cm), and a mass flow controller (MFC, D07-15/ZM, Beijing Sevenstar Electronics Co., Ltd., Beijing, China). Benzene solution and pure water in the volumetric flask was pumped to the sprayer by the peristaltic pump. To get a fine spray and save sample, a fixed flow of 46 mL/min was set for peristaltic pump to transport solution. And then the solution was atomized to be small droplets by the sprayer in the atomizing chamber. As the droplets have large contact areas with air, the dissolved benzene evaporated much more quickly into the air in the atomizing chamber. Then, the air containing benzene vapor, was delivered directly to the PTR-MS under the action of the bypass pump, and detected without pretreatment. The MFC value could be adjusted to control the air flow through the atomizing chamber.

Figure 1. Schematic diagram of the on-line SI-PTR-MS used for rapid and sensitive measurement of benzene dissolved in water.

Chemicals and standard solutions. Benzene and NaCl with analytical reagent grade were obtained from Sinopharm Chemical Reagent Co., Ltd. in China. Benzene is toxic. As the standard solutions, the dilutions of benzene were prepared in water purified on a Milli-Q system (Millipore). Optimization of the carrier gas flow and the salt concentration. In the experiment, laboratory air was used as the carrier gas. During optimizing the flow of carrier gas, 4.4 µg/L of benzene solution was pumped by the peristaltic pump and atomized in spraying extraction system. The MFC value was set to be 0, 10, 20, 30, 40, 50, 60 and 70 standard cubic centimeters per minute (sccm), respectively. PTR-MS monitored the ion intensity of protonated benzene (C6H6·H+ at m/z 79) at every MFC value. The rising curves of ion intensity at m/z 79 were used to estimate the response time of the SI-PTR-MS system, when switched inlet from pure water to benzene solution. After the signal curve reached to its platform, the ion intensity at platform was averaged. In this work, NaCl was added into solution of benzene to investigate the influence of salt concentration on extraction efficiency of benzene. The salt concentration of benzene solution was prepared to be 0, 5%, 10%, 15%, 20% and 25% (W/V), respectively. Analysis of standard solutions. The standard solutions of benzene with different concentrations were atomized in spraying extraction system, and the extracted benzene in carrier gas was monitored by the PTR-MS. 4.4 µg/L of benzene solution was measured for five times to get the repeatability of the method. Analysis of the benzene in real water. The developed method was applied for analysis of trace benzene in different water matrices, including tap water, lake water and waste water. The tap water was obtained from our laboratory and the lake water was obtained from the local source of drinking

ACS Paragon Plus Environment

Page 3 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

water. The waste waters were obtained from a local research institute (RI) and a local biology pharmacy company (BPC), respectively. These water samples were spiked with 4.4 µg/L of benzene to evaluate the recovery of the method. 

another benzene solution with a fixed concentration of 4.4 µg/L. Point A: pure water to benzene solution. The flow of carrier gas was set to 0 sccm.

RESULT AND DISCUSSION

Optimization of the carrier gas flow. In the atomizing chamber, the air was used as equilibrium gas and carrier gas. Its flow was very important to the effect of extraction. Low flow would result in high concentration of benzene but long response time. High flow would result in short response time but low concentration of benzene. Therefore, the air flow was optimized firstly. Eight different air flows, viz., 0, 10, 20, 30, 40, 50, 60, and 70 sccm, were evaluated for shorting response time as well as not obviously decreasing signal intensity. Figure 2(a) and Figure 2(b) show the mass spectrum of pure water and randomly diluted benzene solution tested by the SIPTR-MS, respectively. There is an obvious peak at m/z 79 in Figure 2(b), indicating the protonated benzene. From Figure 2(a) and Figure 2(b), you can see some other obvious peaks at m/z 21, 30, 32, 39, 55 and so on. They can be attributed to H318O+, NO+, O2+, H2O·H218O·H+, (H2O)3·H+ and some interference from peaks with high intensity, respectively. The peaks at m/z 20 and 36 should be the interference from the primary ion peaks with high intensity at m/z 19 (H318O+) and m/z 37 (H3O+·H2O), respectively. To evaluate the response time, the intensity of ion at m/z 79 was monitored when the inlet tube was transferred from pure water to another benzene solution with a fixed concentration of 4.4 µg/L. As shown in Figure 2(c), the intensity of C6H6·H+ increased and lastly reached to a platform when the air flows is 0 sccm. The response time (tres) can be calculated from Figure 2(c) using the calculating method of transient response time for first order system.

Figure 3. The dependence of the C6H6·H+ intensity and the response time of the SI-PTR-MS system on the flow of carrier gas. The flow of carrier gas was set to 0, 10, 20, 30, 40, 50, 60 and 70 sccm, respectively.

Then, the air flow was set to 10, 20, 30, 40, 50, 60, and 70 sccm, respectively. The dependence of the C6H6·H+ intensity and the response time of the SI-PTR-MS system on the flow of carrier gas are shown in Figure 3. The intensities of ion at m/z 79 decreased slowly with the air flow increasing from 0 to 50 sccm, but decreased abruptly with the air flow increasing more than 50 sccm. The response time of the SI-PTR-MS system was 217 s when the MFC was shut. While the MFC value was set to 10 sccm, it quickly reduced to 114 s. It kept decreasing slowly as the MFC value increased from 10 to 50 sccm and became nearly constant afterwards. So, the MFC value was set to 50 sccm in the following experiment. Correspondently, the response time was 55 s. This response time is much shorter than the result in previous study on on-line measurement of benzene in aqueous samples.12, 13 Optimization of salt concentration. According to previous studies, the salt concentration of solution had apparent effect on the extraction efficiency of target compound.10, 33-35 In this study, the effect of salt concentration on the extraction efficiency was evaluated by detecting the benzene solution with different salt concentration. NaCl was added into six samples to prepare different salt concentrations in the range of 0-25% (W/V), viz., 0, 5%, 10%, 15%, 20% and 25%.

Figure 2. Detection of benzene solution with SI-PTR-MS. (a) the mass spectrum of pure water; (b) the mass spectrum of randomly diluted benzene solution; (c) the intensity of ion at m/z 79 was monitored when the inlet tube was transferred from pure water to

The dependence of extraction efficiency on salt concentration is shown in Figure 4. The intensity of ion at m/z 79 detected by SI-PTR-MS increased with the salt concentration rising from 0% to 20% (W/V), and decreased afterwards. According to this result, 20% (W/V) of the salt concentration was selected as the optimum value for the extraction of benzene in water. This result is similar to previous study.10 The reason of

ACS Paragon Plus Environment

Analytical Chemistry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 6

the tendency in Figure 4 could be summarized as the result of two simultaneously processes: forming of hydration spheres around the salt ions and increasing in the viscosity of the solution.10, 36 At the beginning, the former process played the predominant role. These hydration spheres reduced the concentration of available water to dissolve benzene molecules. Hence, the additional benzene molecules were driven to the carrier gas. However, at salt concentration above 20% (W/V), the latter process played the predominant role. The viscosity of the solution increased and therefore the mass transfer rate decreased.

Figure 5. Calibration curve for benzene in water. Fitted equation: y=-50.4+406.4x, R2=0.997. Information of calibration curve for benzene of low concentration range is shown in detail.

Figure 4. The dependence of extraction efficiency on salt concentration. The salt concentration was 0%, 5%, 10%, 15%, 20% and 25%, respectively.

Analysis of standard solutions. After the optimization of the SI-PTR-MS, the air flow and salt concentration were set to 50 sccm and 20% (W/V) in the following experiment, respectively. The standard solutions were analyzed by the SI-PTRMS. The result is shown in Figure 5. From this result, you can see that the calibration curve was linear at least in the range of 0.22-88 µg/L, with a correlation coefficient R2=0.997. And the fitted equation is y = -50.4+406.4x.

Measurement of benzene in real water. To test the applicability of the SI-PTR-MS system in real water samples, it was used for monitoring benzene in different water matrices, such as tap water, lake water and waste water. The tap water was obtained from our laboratory and the lake water was obtained from the local source of drinking water. The waste waters were obtained from a local research institute (RI) and a local biology pharmacy company (BPC), respectively. The waste water (BPC) was diluted one thousand times as the signal was too high. The results were given in Figure 6. Benzene was detected in the two kinds of waste waters. And the concentrations were 13.2 µg/L (RI) and 1.9 µg/L (BPC), respectively. The benzene in tap water and lake water cannot been detected as their concentrations were lower than the LOD of this detection method. In order to investigate the performance of this method, SI-PTR-MS was applied to detect these four kinds of water samples spiked with 4.4 µg/L benzene. As shown in Table 1, the recoveries were in the range of 98% 114%.

The mean background signal intensity and the noise level at m/z 79 can be obtained easily by the SI-PTR-MS. So, combined with the fitted equation above, LOD for benzene in water can be calculated easily. In the experiment, the pure water was analyzed to determine the background signal and the noise level at m/z 79. The dwell time of mass spectrometry was set to 10 s. According the experimental result, the LOD for benzene in water was calculated to be 0.14 µg/L. This LOD level is lower than that of the MI-IMS system by 1 order of magnitude.13 And it is much lower than the MCL of the US EPA4 and EU.5 The repeatability of this method was evaluated with five replicate determinations (4.4 µg/L benzene solution) and the RSD was calculated to be 4.3％. This result is better than some other detection methods of benzene in water. 10, 11, 37

Figure 6. Full scan mass spectra of (a) pure water, (b) tap water, (c) lake water, (d) waste water (RI), and (e) waste water (BPC) diluted one thousand times.

ACS Paragon Plus Environment

Page 5 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Table 1. Concentration (conc.) of benzene in real water and the accuracy of the established method. Real water samples

Conc. (µg/L)

After spiked with 4.4 µg/L benzene(µg/L)

Relative recovery a (%)

Tap water

0.0

5.0

114

Lake water

0.0

4.3

98

Corresponding author *E-mail: [email protected]. Fax: +86-551-65595179.

Notes The authors declare no competing financial interest.



 Waste water (RI)

13.2

17.6

100

Waste water (BPC) diluted one thousand times

1.9

6.5

105

a

Relative recovery (%) = (the mount found in the spiked real sample−the mount in the real sample)/the amount added×100. 4.4 µg/L benzene were spiked into these four kinds of water sample respectively to test the relative recovery of the method. The results demonstrated the satisfactory accuracy of the method for monitoring trace benzene in real water samples. In addition to common ions in mass spectra at m/z 21, 30, 32, 39, and 55, there were 2 kinds of dominant ions at m/z 33 (protonated methanol) and m/z 42 (protonated acetonitrile). And there were some unclear ions in the mass spectra of these water matrices, including m/z 43, m/z 51, m/z 64, m/z 65, m/z 66, m/z 75 and m/z 76. The identification of these ions will be performed in our next work. 

CONCLUSION

A novel and on-line detection method of SI-PTR-MS was introduced for rapid and sensitive monitoring trace benzene in water. The optimized response time of SI-PTR-MS for detection of benzene in water was 55 s. The LOD (0.14 µg/L) was much lower than the MCL of the EU. The SI-PTR-MS system was also applied for monitoring benzene in real water samples. The result suggests that the SI-PTR-MS method can be used for rapid and sensitive monitoring trace benzene and some other VOCs in various water matrices. However, the SI-PTRMS system required a relatively large atomizing chamber; therefore, the chamber will need to be made smaller if the response time needs to be shortened. And the SI-PTR-MS system required a relatively large sample flow of 46 mL/min, so the sprayer and the sampling line should be optimized to detect a small amount sample.



AUTHOR INFORNATION

ACKNOWLEDGEMENT

This work was supported by grants from the National Natural Science Foundation of China (No. 21577145, 21477132, 21107112), the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology, China (No.2014FXCX007), and the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2015BAI01B04).

REFERENCES

(1) Ji, J.; Deng, C. H.; Shen, W. W.; Zhang, X. M. Talanta 2006, 69, 894-899. (2) Vrana, B.; Paschke, A.; Popp, P. Environ. Pollut. 2006, 144, 296307. (3) Irwin, R. J.; Van Mouwerik, M.; Steven, L.; Seese, M. D.; Basham, W. Nat. Park Serv. 1997, Suite 250. (4) http://www3.epa.gov/reg3wcmd/ca/pa/webpages/pad075527804.h tml.. (5) Council Directive 98/83/EC of 3 November 1998 on quality of water intended for human consumption. Off. J. Eur. Commun. 1998, L 330, 0032-0054. (6) Potter, D. W.; Pawliszyn, J. J. Chromatogr. A. 1992, 625, 247-255. (7) Arthur, C. L.; Killam, L. M.; Motlagh, S.; Lim, M.; Potter, D. W.; Pawliszyn, J. Environ. Sci. Technol. 1992, 26, 979-983. (8) Macgillivray, B.; Pawliszyn, J.; Fowlie, P.; Sagara, C. J. Chromatogr. Sci. 1994, 32, 317-322. (9) Lee, M. R.; Chang, C. M.; Dou, J. P. Chemosphere 2007, 69, 1381-1387. (10) Sarafraz-Yazdi, A.; Yekkebashi, A. New J. Chem. 2014, 38, 4486-4493. (11) Mottaleb, M. A.; Abedin, M. Z.; Islam, M. S. Anal. Sci. 2003, 19, 1365-1369. (12) Mohacsi, A.; Bozoki, Z.; Niessner, R. Sensor Actuat. B-Chem. 2001, 79, 127-131. (13) Baumbach, J. I.; Sielemann, S.; Xie, Z. Y.; Schmidt, H. Anal. Chem. 2003, 75, 1483-1490. (14) Ellis, A. M.; Mayhew, C. A. Wiley: NewYork, 2014. (15) Lindinger, W.; Jordan, A. Chem. Soc. Rev. 1998, 27, 347-375. (16) Biasioli, F.; Gasperi, F.; Yeretzian, C.; Märk, T. D. TrAC, Trends Anal. Chem. 2011, 30, 968-977. (17) Lindinger, W.; Hansel, A.; Jordan, A. Int. J. Mass Spectrom. Ion Processes 1998, 173, 191-241. (18) Shen, C. Y.; Li, J. Q.; Han, H. Y.; Wang, H. M.; Jiang, H. H.; Chu, Y. N. Int. J. Mass spectrom. 2009, 285, 100-103. (19) Beale, R.; Liss, P. S.; Dixon, J. L.; Nightingale, P. D. Anal. Chim. Acta 2011, 706, 128-134. (20) Marandino, C. A.; De Bruyn, W. J.; Miller, S. D.; Saltzman, E. S. J. Geophys. Res.: Atmos. 2007, 112, D03301. (21) Visser, A.; Singleton, M. J.; Hillegonds, D. J.; Velsko, C. A.; Moran, J. E.; Esser, B. K. Rapid Commun. Mass Spectrom. 2013, 27, 2472-2482. (22) Louarn, E.; Hamrouni, A.; Colbeau-Justin, C.; Bruschi, L.; Lemaire, J.; Heninger, M.; Mestdagh, H. Int. J. Mass spectrom. 2013, 353, 26-35. (23) Cui, H. P.; Hou, K. Y.; Wu, Q. H.; Hua, L.; Chen, P.; Ju, B. Y.; Li, L.; Wang, Z. X.; Li, J. H.; Li, H. Y. Chinese J. Ana. Chem. 2010,

ACS Paragon Plus Environment

Analytical Chemistry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

5, 760-764. (24) Li, J. Q.; Shen, C. Y.; Wang, H. M.; Han, H. Y.; Zheng, P. C.; Xu, G. H.; Jiang, H. H.; Chu, Y. N. Acta Phys. Chim. Sin. 2008, 24, 705-708. (25) Li, J. Q.; Shen, C. Y.; Wang, H. M.; Han, H. Y.; Zheng P. C.; Xu, G. H.; Jiang, H. H.; Chu, Y. N. Chinese J. Anal. Lab. 2009, 28, 10-14. (26) Kameyama, S.; Tanimoto, H.; Inomata, S.; Tsunogai, U.; Ooki, A.; Yokouchi, Y.; Takeda, S.; Obata, H.; Uematsu, M. Anal. Chem. 2009, 81, 9021-9026. (27) Kameyama, S.; Tanimoto, H.; Inomata, S.; Tsunogai, U.; Ooki, A.; Takeda, S.; Obata, H.; Tsuda, A.; Uematsu, M. Mar. Chem. 2010, 122, 59-73. (28) Shen, C. Y.; Li, J. Q.; Wang, H.Z.; Zhi, Z. H.; Wang, H. M.; Huang, C. Q.; Liu, S.; Jiang, H. H.; Chu Y. N. C. Chinese J. Anal Chem. 2012, 40, 773-777. (29) Li, J. Q.; Shen, C. Y.; Wang, H. M.; Han, H. Y.; Zheng, P. C.; Xu, G. H.; Jiang, H. H.; Chu, Y. N. Chinese J. Anal Chem. 2008, 36,

Page 6 of 6

132-136. (30) Wang, Y. J.; Shen, C. Y.; Li, J. Q.; Wang, H. M.; Wang, H. Z.; Jiang, H. H.; Chu, Y. N. J. Pharm. Biomed. Anal. 2011, 55, 12131217. (31) Jin, S. P.; Li, J. Q.; Han, H. Y.; Wang, H. M.; Chu, Y. N.; Zhou, S. K. Prog. Chem. 2007, 19, 996-1006. (32) Blake, R. S.; Monks, P. S.; Ellis, A. M. Chem. Rev. 2009, 109, 861-896. (33) Aguilera-Herrador, E.; Lucena, R.; Cárdenas, S.; Valcárcel, M. J. Chromatogr. A 2008, 1201, 106-111. (34) Wang, L.; Guo, Y. G.; Liang, S. M.; Yang, Q. Q.; Wei, J. F. J. Chromatogr. Sci. 2011, 49, 671-675. (35) Hashemi, M.; Jahanshahi, N.; Habibi, A. Desalination 2012, 288, 93-97. (36) Kaykhaii, M.; Moradi, M. J. Chromatogr. Sci. 2008, 46, 413-418. (37) Diao, C. P.; Wei, C. H.; Feng, C. H. Chromatographia 2012, 75, 551-555.

For TOC only

ACS Paragon Plus Environment