Environ. Sci. Technol. 1904, 28, 1357- 1360
Formation of Halogenated Artifacts in Brominated, Chloraminated, and Chlorinated Solvents Yuefeng Xle and David A. Reckhow'
Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, Massachusetts 01003 ~~~
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The formation of halogenated solvent artifacts was investigated in common analytical solvents exposed to free chlorine, chloramines, and free bromine. Three brominated solvent artifacts [3-bromo-3-methyl-2-butanol (BMB),l-bromc-2-methyl-2-propanol, and bromoacetone] were identified by gas chromatography/massspectrometry in methyl tert-butyl ether or pentane exposed to free bromine. These same three compounds have been previouslyreported as new disinfection byproducts in ozonated waters high in bromide. A number of chlorinated artifacts, which were reported as novel chloramination byproducts in another previous study, were also identified in diethyl ether exposed to free chlorine and chloramines. The present study indicated that the formation of halogenated artifacts is common in disinfection byproduct (DBP) analysis. Since the formation of artifacts will limit the quantitative and qualitative analysis of DBPs in unquenched water samples, we suggest four ways to avoid the problems related to these artifacts. We also recommend that further research be carried out to verify the results of those studies where known solvent artifacts are reported as byproducts of drinking water disinfection.
et al. reported the formation of both brominated and chlorinated artifacts (14). Recently, bromohydrins, bromoacetone, and a number of chloraminated DBPs have been reported in ozonated or chloraminated waters (15-18). In all these studies, organic solvents were used to extract unquenched samples (i.e., containing either free or combined residual halogen). The analysis of natural organic matter (NOM) -free blanks was either not reported or reported in insufficient detail to be able to judge the results. Due to the possible formation of halogenated solvent artifacts, it is not clear if these are actual DBPs formed in water or artifacts formed at the time of extraction (19). Pentane, methyl tert-butyl ether (MTBE), and diethyl ether are common organic solvents for DBP analysis in drinking water. Despite their widespread use, little or no work has been reported on the formation of halogenated artifacts in these solvents. Therefore, the objectives of the present research were to study the formation of analytical artifacts in pentane, MTBE, and diethyl ether exposed to free chlorine, chloramines,or free bromine and to suggest ways of avoiding problems related to those artifacts. Experimental Section
Introduction Since chloroform was first reported in drinking water in the 19709, a number of other disinfection byproducts (DBPs) have been found in chlorinated drinking waters. These DBPs include the well-known trihalomethanes, haloacetic acids, chloral hydrate, chloropicrin, chloroacetones, and some recently reported brominated haloacetic acids, brominated trihaloacetaldehydes, and brominated trihalonitromethanes (1-5).Alternative disinfectants such as ozone or chloramines have been used in water treatment to control the formation of chlorinated DBPs (6). However, a number of DBPs have also been reported in ozonated or chloraminated waters. These DBPs include aldehydes, keto acids, carboxylic acids and cyanogen halides (7-11). Liquid-liquid extraction with organic solvents is the most common separation technique for the analysis of DBPs in water. Several groups of researchers have noted that unique artifacts can form when water disinfectant residuals are allowed to come into contact with these solvents. Ibrahim et al. found a number of chlorinated artifacts in the extracts of chlorinated water (12). These artifacts, chlorinated cyclohexene derivatives, were reported as reaction products of the cyclohexene preservative in dichloromethane with residual chlorine in the water sample. It was also found that the addition of ammonia, which converts free chlorine to chloramines, minimized the problem somewhat; however, it was clearly not a final solution. Dietrich et al. reported similar results on chlorinated cyclohexene artifacts and found that dechlorination with sodium arsenite significantly inhibited the formationof most chlorinated artifacts (13). Working with dichloromethane extracta of waters high in bromide, Wang 0013-936X/94/0928-1357$04.50/0
0 1994 American Chemlcal Society
Reagents. Solvents used in this work included organic residual analysis-grade pentane (J.T. Baker Inc.), residual analysis-grade MTBE (EM Science), and organic residual analysis-grade diethyl ether (J. T. Baker Inc.). One bromohydrin compound, 3-bromo-2-methyl-2-butanol (BMB), was synthesized in the authors' laboratory (ZO), and bromoacetone was obtained from a commercial source (Chem Service, Inc.). Reagent water was prepared by reverse osmosis and resin adsorption (Millipore Corp.). Solutions of bromine, chlorine, and monochloramine were prepared in reagent water, and their concentrations were determined by DPD titration (21). Sample Preparation. For the study of artifacts in brominated solvents, 500 mL of 0.1 mM bromine solution was extracted with 100 mL of either pentane or MTBE. The extraction was conducted in a separatory funnel, and the contact time between the phases was 5 min. The extract was dried with sodium sulfate and concentrated under a gentle nitrogen flow to about 50 pL. About 2 pL of the concentrated extract was injected into the GC in the splitless mode. For the study of artifacts in chloraminated or chlorinated diethyl ether, 50 mL of a 31 mg/L monochloramine or free chlorine solution was extracted with the solvent in a separatory funnel for 5 min. The extract was dried with sodium sulfate, then concentrated to dryness under a gentle nitrogen flow, and redissolved in 250 pL of methanol containing 14% (v/v) boron trifluoride. After 12h of reaction time at 70 "C, the mixture was neutralized with 3 mL of 2 % sodium bicarbonate and then extracted with 2 X 300 p L of hexane. The combined extracts were concentrated to about 50 pL under a gentle nitrogen stream and submitted for GC/MS analysis. This Environ. Sci. Technol., Vol. 28, No. 7, 1994
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procedure was similar to the sample preparation method reported by Kanniganti et al. (18). G U M S Qualitative Analysis. Gas chromatography/ mass spectrometry (GC/MS) analyses were performed on an HP-5890 gas chromatograph coupled to an HP-5988 quadrupole mass spectrometer (Hewlett-Packard). A 30 m X 0.32 mm i.d., 0.25-pm film thickness PTE-5 capillary column (Supelco) was used for all analyses. For the analysis of bromine extracts, the column oven was kept at 30 "C for 10 min, then ramped to 200 "C at a rate of 25 "C/min, and held at 200 "C for 5 min. For monochloramine or chlorine extracts, the column oven was kept at 30 "C for 2 min, then ramped to 250 "C at a rate of 5 "Urnin, and held at 250 "C for 5 min. For all analyses, the injector temperature was at 200 "C and the transfer line was kept at 280 "C. The mass spectrometer was tuned with perfluorotributylamineimmediately before analysis. The mass spectra were obtained in the electron impact (EI) mode at a 200 "C ion source temperature and an electron energy of 70 eV while scanning over a mass range of 30400 amu. Other G U M S operating conditions were similar to those reported in a previous study (22). GC/MS Quantitative Analysis. Quantitative measurements were only made for the study of BMB degradation in the presence of thiosulfate. A 40-mL aqueous sample was extracted with 4 mL of MTBE spiked with a 500 pg/L internal standard, 1,2-dibromopropane. The extract was then dried with sodium sulfate and concentrated to about 50 pL. Since these samples only contained BMB, the chromatograms were very clean, and a selected ion monitoring (SIM) mode was used to increase G U M S sensitivity. The ions chosen for analysis were 59 for 3-bromo-2-methyl-2-butanol (BMB) and 121 for the internal standard. Other G U M S operating conditions were similar to those described in the previous section.
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Results and Discussion The total ion chromatogram of brominated MTBE extract is shown in Figure 1. A number of the peaks, marked with asterisks, represent brominated compounds as evidenced by the unique isotopic clusters for bromine in their E1 mass spectra. Figure 2 shows nearly identical mass spectra for compounds found in brominated MTBE and brominated pentane. This byproduct commonto both solvents has been identified as BMB based on the comparison of retention time and mass spectrum with a pure standard (bottom, Figure 2). Another major bro1358 Envlron. Scl. Technol., Vol. 28, No. 7. 1994
mohydrin, 1-bromo-2-methy1-2-propano1, was tentatively identified in brominated MTBE but not in brominated pentane. This mass spectrum is shown in Figure 3. Another mass spectrum (also Figure 3), obtained in the brominated MTBE, was from a compound identified as bromoacetone. As with BMB, this identification was confirmed by comparison of its retention time and mass spectrum with those of a standard. Bromohydrins have been reported as a new group of ozonation byproducts formed in waters high in bromide (15-17). One of the bromohydrins, BMB, was reported at
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Flgure 4. Mass spectra of three solvent artifacts in chioraminated diethyl ether. a level (about 250 pg/L) exceeding that of the THMs (15). Bromoacetone,identified here as an artifact in brominated MTBE, was also reported a t a level (46pg/L) similar to that of the THMs (17).It is not clear that appropriate NOM-free blanks were analyzed in these studies. For example, one study (15)included the analysis of a sample that was pretreated to remove organic matter prior to ozonation. Unfortunately, the nature of the inorganic matrix at the time of ozonation and extraction was not reported. Without this information, one cannot determine if the solvent was exposed to the same residual bromine concentration in both samples and blanks. While bromoacetone and bromohydrins may be true oxidation byproducts of NOM, the present study shows that they may also occur as solvent artifacts. Careful work is needed to distinguish between the two. A number of chlorinated solvent artifacts were also found in chlorinated and chloraminated diethyl ether. Three E1 mass spectra that resemble reported chloramination byproducts of fulvic acid (peak nos. 1,4,and 10 in ref 18) were obtained in a chloraminated diethyl ether sample, as shown in Figure 4. These were tentatively identified by Kanniganti et al. as chlorinated acetals. Methylated dichloroacetic acid and methylated trichloroacetic acid were also identified in chloraminated diethyl ether. Three E1 mass spectra (Figure 5), which also resemble those reported as chloramination byproducts of fulvic acid (peak nos. 13,14, and 16 in ref 18)were identified in chlorinated diethyl ether. These were tentatively identified as chlorinated ethers (18). The elution order of the peaks identified in the present study is the same as that reported by Kanniganti et al. (18).In the previous study, 46 novel chloramination byproducts were reported in a monochloraminated fulvic acid solution. An unchlorinated fulvic acid blank was also run. However, it cannot be used to
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Figure 5. Mass spectra of three solvent artifacts In chlorlnated diethyl ether. check for the formation of chlorinated solvent artifacts since no chlorine was ever present. Because appropriate NOM-free blanks were not reported, it is not clear if those chlorinated compounds were actual chloramination DBPs or solvent artifacts. Since the formation of solvent artifacts is a common phenomenon, we propose four approaches to reduce their impact on DBP analysis. The first approach is to use several independent analytical methodologies (e.g., different solvents). Care must be taken with this approach as it has already been shown that the same solvent artifact can be observed with very different solvents. The second approach is to purify the organic solvent (23). This presumes that the artifact precursors are solvent contaminants that can be removed by distillation or some other technique. Whether or not this is true can only be determined by testing the solvent with residual oxidants. The third approach would be to analyze an appropriate NOM-free blank. This could warn the analyst of the possible formation of solvent artifacts. Still,this approach has two weaknesses. First, it may not be possible to remove NOM from a water without affecting the inorganic matrix. Second, NOM itself may influence the behavior of oxidants and their reaction with the inorganic matrix and subsequently with the extraction solvent. A fourth approach is to stabilize or reduce residual inorganic oxidant prior to analysis. This technique has been widely used for the analysis of chlorinated byproducts in water. By taking this approach, however, one runs the risk of destroying labile organic byproducts in the process. For this reason, we examined the stability of BMB in the presence of two common reducing agents, sulfite and thiosulfate. Sulfite reduced 200 pg/L of BMB below the Envlron. Sci. Technol., Vol. 28, No. 7, 1994 1369
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support of this research under Grant BCS-8958392. Thanks also go to the Hewlett-Packard Co. and its university equipment grant program for their generous financial assistance.
Literature Cited Reckhow, D. A.; Singer, P. C. J. Am. Water Works Assoc. 1990, 82 (4), 173-180.
Krasner, S . W.; McGuire, M. J.; Jacangelo, J. G.; Patania, N. L.; Reagan, K. M.; Aieta, E. M. J. Am. Water Works ASSOC. 1989,81 (8), 41-53. Pourmoghaddas, H.; Stevens, A. A.; Kinman, R. N.; Dressman, R. C.; Moore, L. A.; Ireland, J. C. J. Am. Water Works ASSOC. 1993,85 (l),82-87. Xie, Y.; Reckhow, D. A. Analyst 1993, 118, 71-72. Thibaud, T.; De Laat, J.; Dore, M. Water Res. 1988, 22,
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Figure 6. Degradationof BMB in the presence of 5 mM of thiosulfate at pH 7.0. detection limit in 20 min at room temperature. This indicates that sulfite cannot be used as aquenching reagent for bromohydrin analysis. The degradation of BMB in the presence of 5 mM of thiosulfate at 20 "C and pH 7 is shown in Figure 6. The pseudo-first-order reaction rate constant was estimated as 1.5 f 0.4 X lo4 s-l. Under the present experimental conditions, the half-life of BMB is about 1.3 h. Since sample extraction only takes about 5-10 min, thiosulfate may be a suitable quenchingreagent for bromohydrin analysis. Further study may show that other reducing agents are superior to thiosulfate.
Conclusions
Bromohydrins were identified as solvent artifacts in brominated pentane and MTBE. Bromoacetone was also found to be a solvent artifact in brominated MTBE. A number of mass spectra that are identical to those of reported chloramination byproducts were also found in diethyl ether exposed to free chlorine and chloramines. Since these compounds have been reported as novel disinfection byproducts in water, we recommend that further study be carried out to fully distinguish between what is present in the sample prior to analysis and what is formed during sample workup and analysis. We also recommend that appropriate NOM-free blanks and chemically-reduced samples be analyzed whenever new disinfection byproducts are identified. Acknowledgments
We express our appreciation to the US. National Science Foundation and Dr. Edward H. Bryan for their financial
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381-390.
Rice, R. G. Ozone Sci. Eng. 1980,2, 75-99. Yamada, H.; Somiya, I. Ozone Sci. Eng. 1989,11,125-141. Glaze,W. H.; Koga, M.; Cancilla, D. Environ. Sci. Technol. 1989,11,1177-1181.
Xie, Y.; Reckhow,D. A. Ozone Sci. Eng. 1992,14,269-275. Andrews,S. Ph. D. Dissertation,University of Alberta, 1993. Xie, Y.; Reckhow, D. A. Water Res. 1993,27, 507-511. Ibrahim, E. A.; Lippincott, R. L.; Brenner, L.; Suffet, I. H. J. Chromatogr. 1987,393, 237-253. Dietrich, A. M.; Christman, R. F.; Durell, G. S. Biomed. Environ. Mass Spectrom. 1988, 15, 453-458.
Wang, D. T.; Meresz, 0.;Taguchi,V. Y.; Jenkins, S. W. D.; Robinson, D. Anal. Lett. 1988,21, 1749-1756. Cavanagh, J. E.; Weinberg, H. S.; Gold, A.; Sangalah, R.; Marbury, D.; Glaze, W. H.; Collette, T. W.; Richardson, S. D.; Thurston, A. D. Environ. Sci. Technol. 1992,26,16581662.
Cavanagh, J. E. M.S. Thesis, University of North Carolina at Chapel Hill, 1991. Glaze,W. H.;Weinberg,H. S.;Cavanagh,J. E. J.Am. Water Works ASSOC. 1993,85 (l),96-103.
Kanniganti, R.; Johnson, J. D.; Ball, L. M.; Charles, M. J. Environ. Sei. Technol. 1992,26, 1998-2004. Xie, Y.; Reckhow,D. A. In Proceedings of the A W W A Water Quality Technology Conference; AWWA Denver, CO, 1993; pp 1499-1511. Langman, A. W.; Dalton, D. R.; Reingold, I. D.; Masamune,
S. Org. Synth. 1980,59, 16-20. Standard Methods for the Examination of Water and Wastewater,18th ed.;American Public Health Association,
American Water Works Association, and Water Environment Federation: Washington, DC, 1992. Xie, Y.; Rajan, R. V.; Reckhow,D. A. Org. Mass Spectrom. 1992,27,807-810.
Perrin, D. D.; Armarego,W. L. F. Purification of Laboratory Chemicals,3rd ed.;Pergamon Press: Oxford,England, 1988. Received for review December 6, 1993. Revised munuscript received March 15, 1994. Accepted March 23, 1994.'
@Abstractpublished in Advance ACS Abstracts, April 15,1994.
