Determination of Chlorinated Paraffins by Bromide-Anion Attachment

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Letter Cite This: Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX

pubs.acs.org/journal/estlcu

Determination of Chlorinated Paraffins by Bromide-Anion Attachment Atmospheric-Pressure Chemical Ionization Mass Spectrometry Bo Yuan,*,† Jonathan P. Benskin,† Chang-Er L. Chen,‡ and Åke Bergman§ †

Department of Environmental Science and Analytical Chemistry, Stockholm University, Svante Arrhenius väg 8, SE-10691 Stockholm, Sweden ‡ Environmental Research Institute, MOE Key Laboratory of Environmental Theoretical Chemistry, South China Normal University, 510006 Guangzhou, China § Unit of Toxicology Sciences, Swetox, Karolinska Institutet, Forskargatan 20, SE-151 36 Södertälje, Sweden S Supporting Information *

ABSTRACT: A novel method for the quantitative determination of chlorinated paraffins (CPs) was developed using bromide-anion attachment atmospheric-pressure chemical ionization mass spectrometry (APCI-MS). Bromoform was used to enhance ionization of CPs. Near exclusive formation of stable bromide adduct ions ([M + Br]−) enabled accurate detection of individual CP congener groups (CnClm) with only a moderate-resolution quadrupole time-of-flight mass spectrometer. Furthermore, the method was free from interference commonly observed with chloride-anion attachment methods (e.g., decomposition ions [M + Cl − HCl]−) that require deconvolution. Together with a CnClm-response-factor algorithm for quantifying short-chain CPs and a CnClm-pattern-reconstruction algorithm for quantifying medium- and long-chain CPs, method applicability was demonstrated on biota and sediment samples. These data were generated significantly faster and with improved selectivity and sensitivity versus those of conventional measurements by chloride-anion attachment APCI-MS.

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gener groups with five more carbons and two fewer chlorines (i.e., Cn+5Clm−2) produce overlapping signals by low-resolution MS (e.g., quadrupole).22 Hence, to resolve SCCPs from MCCPs, and MCCPs from LCCPs, requires a moderately highresolution MS such as quadrupole time of flight (QTOF).20,23 However, [M + Cl]− ions of CnClm groups have the same nominal masses as other homohalogen ions, in particular decomposition ions (e.g., [M + Cl − xHCl]−, where x ≥ 1) of other CnClm groups.24 Hence, accurate determination of individual CnClm groups requires either a MS resolution of >50000 (e.g., Orbitrap25) or deconvolution of mass spectra obtained from a moderate-resolution mass spectrometer,26 which is time-consuming for hundreds of CnClm groups per analyte.15 Another option for distinguishing individual CnClm groups involves formation of heterohalogen CP adduct ions, for example, by introducing a halogen other than chlorine into the ion source. A comparison of the performance of Cl-anion attachment and bromide (Br)-anion attachment for determination of β-lactam antibiotics using APCI-MS revealed that [M

INTRODUCTION Chlorinated paraffins (CPs) represent a diverse mixture of polychlorinated straight-chain alkanes (CnH2n+2−mClm, where n = 6−38)1,2 commonly used as plasticizers, flame retardants, and metal cutting fluids. Short-chain (C10−13, SCCPs), mediumchain (C14−17, MCCPs), and long-chain CPs (C≥18, LCCPs) are the most common commercial CP mixtures.3 Annual global production exceeds 1 million tons, making CPs extremely highproduction volume chemicals.1 SCCPs were added to the Stockholm Convention on persistent organic pollutants (POPs) in 2017;4 consequently, production of alternatives such as MCCPs and LCCPs is expected to increase.5 Recent studies have reported on the global occurrence of SCCPs, MCCPs, and LCCPs in sewage sludge,6,7 soil,8 sediment cores,9 wildlife,10,11 indoor environments,12−15 human blood and tissue,16,17 and mothers’ milk,18,19 highlighting the need to characterize health risks associated with CPs. Determination of CPs in environmental samples is technically challenging. Simultaneous analysis of SCCPs, MCCPs, and LCCPs is commonly performed using direct liquid injection chloride-anion attachment atmospheric-pressure chemical ionization mass spectrometry (Cl-anion attachment APCI-MS) using chloroform or dichloromethane.20,21 CPs are measured as chloride adduct ions [M + Cl]− of individual carbon−chlorine congener (CnClm) groups. Con© XXXX American Chemical Society

Received: Revised: Accepted: Published: A

April April April April

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2018 2018 2018 2018 DOI: 10.1021/acs.estlett.8b00216 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX

Letter

Environmental Science & Technology Letters

Table 1. Chlorinated Paraffin Results for Biota and Sediment Samples Analyzed by Br-Anion Attachment APCI-QTOF-MS concentration (ng/g of lipid or ng/g of dry sediment)

chlorine content (%)

sample

sampling year

n

location, country

SCCPs

MCCPs

LCCPs

SCCPs

total CPs

herring (fillet) common dab (fillet) salmon (fillet) flounder (tissue) blue mussel (tissue) commercial blue mussel (tissue) surface sediment core-top sediment (2016) sediment core section (1996) sediment core section (1990) sediment core section (1985)

2008 2014 2014 2014 2013 2016 2013 2016 2016 2016 2016

10 >10 >10 >10 >10 >10 − − − − −

Landsort, Sweden The Westerscheldt, The Netherlands Atlantic Ocean The Westerscheldt, The Netherlands Ijmuiden harbor, The Netherlands Chile Himmerfjärden, Sweden Himmerfjärden, Sweden Himmerfjärden, Sweden Himmerfjärden, Sweden Himmerfjärden, Sweden

81 1300 280 1100 900 770 7.3 6.8 9.5 13 28

500 790 220 1100 1500 2200 21 14 11 24 46

81 77 37 140 440 650 190 26 73 170 300

50 52 50 49 49 52 53 55 56 55 57

51 49 52 50 53 52 46 51 47 46 46

+ Br]− ions were more stable and sensitive than [M + Cl]− ions.27 We therefore hypothesized that Br-anion attachment may be a promising alternative for determination of CPs. This work describes the development and validation of such a method, using bromoform as a source of Br ions. The method improves the sensitivity and selectivity relative to those of conventional methods and takes less time for data processing because of a lack of signal overlap.

cane, 2,3,4,5,6,7,8,9-octachlorodecane, and 1,2,3,4,5,6,7,8,9nonachlorodecane (Dr. Ehrenstorfer GmbH, Augsburg, Germany), followed by two commercial mixtures of SCCPs (SCCP 63.0%Cl, Dr. Ehrenstorfer GmbH; Hüls 70C, Hüls AG), a commercial MCCP mixture (Cereclor S52, INEOS Chlor Ltd.), and a commercial LCCP mixture (LCCP 49.0%Cl, Dr. Ehrenstorfer GmbH). Next, we calculated theoretical m/z ratios of adduct ions ([M + Br]−) and their isotopic abundances. The two most abundant m/z ratios were selected for quantification. Instrumental settings for Br-anion attachment APCI-QTOF-MS were subsequently optimized to maximize signal intensities of [M + Br]− ions of CnClm groups using a solution of 25 ng/μL SCCP 63.0%Cl as a reference. Finally, we applied a recently introduced CnClm-response-factor (RF) algorithm26 and commercial mixtures of single-chainlength CPs together with the Br-anion attachment APCIQTOF-MS for quantifying short-chain CPs in six pooled biota samples and five sediment samples. For quantifying MCCPs and LCCPs, because of a lack of single-chain-length commercial mixtures, we applied a CnClm-pattern-reconstruction algorithm developed by Bogdal et al.20 SCCPs, MCCPs, and LCCPs in these samples were also quantified using Cl-anion attachment APCI-QTOF-MS combined with identical reference standards and quantification algorithms. The biota samples were collected from Sweden, The Netherlands, Chile, and the Atlantic Ocean, while sediments were collected from Sweden (see Table 1). Detailed information about sample preparation, quantification, and quality assurance/quality control (QA/QC) is given in Texts S3−S5 and Figure S1 of the Supporting Information.

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MATERIALS AND METHODS Target analytes dissolved in cyclohexane were analyzed using an APCI-QTOF-MS instrument (QTOF Premier, Waters, Manchester, U.K.) operated in full scan (m/z 300−1040), negative ion mode with an observed resolution of 9000−10000. The injection volume was 5 μL, and the flow rate of the mobile phase (hexane) was 0.150 mL/min. Bromoform (Merck KGaA, Darmstadt, Germany) was introduced into the mobile phase downstream of the injector, as described previously.20 The optimized settings for the MS were as follows: collision energy of 2.6 V, cone voltage of 20 eV, ion source temperature of 105 °C, ion probe temperature of 300 °C, desolvation gas flow rate of 800 L/h, and cone gas flow rate of 90 L/h. A solution of bromoform in hexane [1:2 (v/v)] was added to a syringe (10.0 mL, model 1010, Hamilton Co.) and then introduced into the mobile phase via a syringe pump at a flow rate of 0.01 mL/min to give a final concentration of 2% (v/v) in the mobile phase. Instrumental contamination is a concern when using high concentrations of organohalogen solvents. Fortunately, the use of a syringe pump facilitates introduction of small quantities of bromoform while avoiding contact with the LC system. Since switching over to bromoform (from dichloromethane), we have not observed source contamination or a deterioration of instrumental performance. For comparison, all samples and standards were analyzed by both Br- and Cl-anion attachment APCI-QTOF-MS methods. Data processing was performed using MassLynx version 4.1. All data were backgroundsubtracted. Instrumental limits of detection (LODs) of individual CnClm groups, MCCP mixtures, and LCCP mixtures were calculated on the basis of the concentration producing a signal-to-noise ratio of 3:1 (Table S2). Detailed information about chemicals and instrumental settings of Cl-anion attachment APCI-QTOF-MS techniques is provided in Texts S1 and S2 of the Supporting Information. We first investigated fragmentation of a CP congener mixture standard “MIX-2” consisting of 1,2,5,6,9-pentachlorodecane, 1,2,4,5,9,10-hexachlorodecane, 1,2,4,5,6,9,10-heptachlorode-

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RESULTS AND DISCUSSION Performance of Br- versus Cl-Anion Attachment. The mass spectra of MIX-2 analyzed using both Br- and Cl-anion attachment methods are provided in Figure 1. With bromoform, congeners C10Cl5 to C10Cl9 formed nearly exclusive [M + Br]− adduct ions. Other adducts such as [M + Br − HCl]− or [M + Br − HBr]− were not observed. In contrast, chlorideanion attachment produced [M + Cl]− ions for C10Cl5 to C10Cl8 congeners that overlapped with [M + Cl − HCl]− ions produced from C10Cl6 to C10Cl9 congeners. A [M + Cl − HCl]− ion of C10Cl5 was also identified. The neutral loss of the conjugate acid of fluoride (F)-, Cl-, and Br-anion adducts has been previously observed.28,29 In that work, F-anion adducts displayed the greatest potential to decompose via loss of HF. Additional Br adducts (e.g., [M + Br − HCl]− or [M + Br − B

DOI: 10.1021/acs.estlett.8b00216 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX

Letter


ing to the C10Cl8 congener group) and individual mixtures of (ii) C11Cl6 and (iii) C11Cl9 isomers, obtained using Br- and Clanion attachment methods, respectively. Figure S2 shows the results for individual mixtures of (iv) C14Cl6 and (v) C18Cl6 isomers. The measured isotopic distributions (i.e., predeconvolution) of [M + Br]− ions of the five CnClm congener groups agreed with their theoretical isotopic distributions (i.e., postdeconvolution), suggesting that deconvolution would not improve the measurement. This was confirmed by an absence of change in the isotopic distributions of [M + Br]− following deconvolution (Figure 2). In contrast, [M + Cl]− ions of CnClm groups were unresolved from [M + Cl − HCl]− ions produced from CnClm+1 groups. As a result of this overlap, signals for the five CnClm groups measured by Cl-anion attachment MS could be overestimated by 1.4−39%, in the absence of deconvolution. Clearly a major advantage of the Br-anion attachment method is the absence of a mass overlap deconvolution step, which is tedious but necessary to resolve hundreds of [M + Cl]− ions from overlapping signals produced by [M + Cl − HCl] − ions. In contrast, heterohalogen ions (i.e., CnH2n+2−mClmBr) are easily resolved from other ions with a theoretical minimum MS resolution of 6500. Such a resolution is sufficient to resolve nominal masses between congener groups with five more carbons and two fewer chlorines22 [e.g., C 24 H 32 Cl 18 Br − (1036.5963 amu) and C 29 H 44 Cl 16 Br − (1036.7554 amu)], which can be achieved with a moderately high-resolution MS such as the QTOF MS used here.

Figure 1. Br- and Cl-anion attachment mass spectra of five CP congeners in a congener mixture standard (MIX-2).

HBr]−) might be absent because decomposition via departure of Br− is preferred to loss of neutral HBr. Figure 2 shows isotopic distributions of both [M + Br]− and [M + Cl]− ions pre- and postdeconvolution24 for (i) an authentic standard of 2,3,4,5,6,7,8,9-octachlorodecane (belong-

Figure 2. Pre- and postdeconvlution of Br- and Cl-anion attachment mass spectra of 2,3,4,5,6,7,8,9-octachlorodecane (C10Cl8), the C11Cl6 congener group, and the C11Cl9 congener group in technical mixtures MIX-2, SCCP 63.0%Cl, and Hüls 70C, respectively. C


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Figure 3. CnClm patterns in the environmental samples derived with the Br-anion attachment method. The X-axis represents carbon-chain length, and the Y-axis represents the relative abundances of individual congener groups.

these solvents should follow strict safety instructions, including the use of proper personal protective equipment to minimize the potential for human exposure. Application to Environmental Samples. SCCP, MCCP, and LCCP concentrations in six biota samples and five sediment samples using both Br- and Cl-anion attachment methods are listed in Table 1 and Table S3, respectively. CnClm patterns of CPs in salmon, Chilean mussels, and Swedish sediment are shown in Figure 3, while percent compositions of SCCP CnClm in all samples are listed in Table S4. The concentrations of SCCPs, MCCPs, and LCCPs in fish and mussels were 81−1300, 220−2200, and 37−650 ng/g of lipid weight, respectively. LCCPs were present in all samples, while SCCPs or MCCPs accounted for 14−60 and 36−86% of total CPs, respectively. In Swedish sediments, SCCP, MCCP, and LCCP concentrations generally decreased from 28 to 6.8 ng/g of dry sediment, from 46 to 14 ng/g dry of sediment, and from 300 to 26 ng/g of dry sediment, respectively, between 1985 and 2016. LCCPs predominated in all sediment samples, accounting for 56−87% of total CPs. SCCP, MCCP, and LCCP concentrations quantified using Br-anion attachment were 76−129, 73−118, and 55%−163%, respectively, of the concentrations determined by Cl-anion attachment (Table S3), demonstrating the reasonable consistency of the methods. Potential risks from all three CP groups highlight the urgent need for a rapid and reliable analytical technique, such as the one developed here.

This might also be advantageous for determining CP-like substances such as chlorinated alkenes (CP-enes; i.e., unsaturated CPs). Recently, CP-enes have been identified as dehydrochlorination products of CPs30,31 and also have been observed in several CP commercial mixtures as well as in the atmosphere.25 Similar to those used for CPs, standard methods for analyzing CP-enes involve Cl-anion attachment.30 The m/z ratio of [M + Cl]− for CP-enes (CnH2n−mClm+1) is identical to that of [M + Cl − HCl]− for CnClm+1 CPs; consequently, it is impossible to distinguish CPs from CP-enes present in the same sample. Because Br-anion attachment does not produce ions that overlap with CP-enes, this new method provides a possible solution for interference-free analysis of CP-enes. The m/z values of [M + Br]− ions for quantification are listed in Table S1. Instrumental RFs of short-chain CnClm groups were calculated using corresponding single-chain-length reference standards according to our recent work,26 the values of which are listed in Table S2. Instrumental responses in the new method were greater than those of the Cl-anion attachment method, resulting in LODs for most SCCPs, MCCPs, and LCCPs that were an average of 2-fold lower than those of the Cl-anion attachment method. RFs were generally highest for CnClm groups with a moderate number of chlorines on the carbon chain. Similar trends for CnClm group RFs have also been found when using Cl-anion attachment APCI-QTOFMS, GC-electron capture negative ionization (ECNI)-magnetic sector MS, and GC-ECNI-Q-Orbitrap-MS.26 The level of the halogenated solution was reduced from 10% (v/v) dichloromethane20 or 30% chloroform21 to 2% bromoform. However, it should be noted that bromoform is more toxic than chloroform and dichloromethane (occupational exposure limits of 5, 9.78, and 86.7 mg/m3 for bromoform, chloroform, and dichloromethane, respectively).32 The use of

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.estlett.8b00216. D


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(11) Cariou, R.; Omer, E.; Leon, A.; Dervilly-Pinel, G.; Le Bizec, B. Screening halogenated environmental contaminants in biota based on isotopic pattern and mass defect provided by high resolution mass spectrometry profiling. Anal. Chim. Acta 2016, 936, 130−8. (12) Wong, F.; Suzuki, G.; Michinaka, C.; Yuan, B.; Takigami, H.; de Wit, C. A. Dioxin-like activities, halogenated flame retardants, organophosphate esters and chlorinated paraffins in dust from Australia, the United Kingdom, Canada, Sweden and China. Chemosphere 2017, 168, 1248−1256. (13) Gallistl, C.; Lok, B.; Schlienz, A.; Vetter, W. Polyhalogenated compounds (chlorinated paraffins, novel and classic flame retardants, POPs) in dishcloths after their regular use in households. Sci. Total Environ. 2017, 595, 303−314. (14) Gao, W.; Cao, D.; Wang, Y.; Wu, J.; Wang, Y.; Wang, Y.; Jiang, G. External Exposure to Short- and Medium-Chain Chlorinated Paraffins for the General Population in Beijing, China. Environ. Sci. Technol. 2018, 52 (1), 32−39. (15) Yuan, B.; Strid, A.; Darnerud, P. O.; de Wit, C. A.; Nyström, J.; Bergman, Å. Chlorinated paraffins leaking from hand blenders can lead to significant human exposures. Environ. Int. 2017, 109, 73−80. (16) Li, T.; Wan, Y.; Gao, S.; Wang, B.; Hu, J. High-Throughput Determination and Characterization of Short-, Medium-, and LongChain Chlorinated Paraffins in Human Blood. Environ. Sci. Technol. 2017, 51 (6), 3346−3354. (17) Wang, Y.; Gao, W.; Wang, Y.; Jiang, G. Distribution and Pattern Profiles of Chlorinated Paraffins in Human Placenta of Henan Province, China. Environ. Sci. Technol. Lett. 2018, 5 (1), 9−13. (18) Xia, D.; Gao, L.; Zheng, M.; Li, J.; Zhang, L.; Wu, Y.; Tian, Q.; Huang, H.; Qiao, L. Human Exposure to Short- and Medium-Chain Chlorinated Paraffins via Mothers’ Milk in Chinese Urban Population. Environ. Sci. Technol. 2017, 51 (1), 608−615. (19) Xia, D.; Gao, L. R.; Zheng, M. H.; Li, J. G.; Zhang, L.; Wu, Y. N.; Qiao, L.; Tian, Q. C.; Huang, H. T.; Liu, W. B.; Su, G. J.; Liu, G. R. Health risks posed to infants in rural China by exposure to short- and medium-chain chlorinated paraffins in breast milk. Environ. Int. 2017, 103, 1−7. (20) Bogdal, C.; Alsberg, T.; Diefenbacher, P. S.; MacLeod, M.; Berger, U. Fast quantification of chlorinated paraffins in environmental samples by direct injection high-resolution mass spectrometry with pattern deconvolution. Anal. Chem. 2015, 87 (5), 2852−60. (21) Zencak, Z.; Oehme, M. Chloride-enhanced atmospheric pressure chemical ionization mass spectrometry of polychlorinated n-alkanes. Rapid Commun. Mass Spectrom. 2004, 18 (19), 2235−40. (22) Reth, M.; Oehme, M. Limitations of low resolution mass spectrometry in the electron capture negative ionization mode for the analysis of short- and medium-chain chlorinated paraffins. Anal. Bioanal. Chem. 2004, 378 (7), 1741−7. (23) Gao, W.; Wu, J.; Wang, Y.; Jiang, G. Quantification of short- and medium-chain chlorinated paraffins in environmental samples by gas chromatography quadrupole time-of-flight mass spectrometry. J. Chromatogr A 2016, 1452, 98−106. (24) Yuan, B.; Alsberg, T.; Bogdal, C.; MacLeod, M.; Berger, U.; Gao, W.; Wang, Y.; de Wit, C. A. Deconvolution of Soft Ionization Mass Spectra of Chlorinated Paraffins To Resolve Congener Groups. Anal. Chem. 2016, 88 (18), 8980−8. (25) Li, T.; Gao, S.; Ben, Y.; Zhang, H.; Kang, Q.; Wan, Y. Screening of Chlorinated Paraffins and Unsaturated Analogues in Commercial Mixtures: Confirmation of Their Occurrences in the Atmosphere. Environ. Sci. Technol. 2018, 52 (4), 1862−1870. (26) Yuan, B.; Bogdal, C.; Berger, U.; MacLeod, M.; Gebbink, W. A.; Alsberg, T.; de Wit, C. A. Quantifying Short-Chain Chlorinated Paraffin Congener Groups. Environ. Sci. Technol. 2017, 51 (18), 10633−10641. (27) Horimoto, S.; Mayumi, T.; Aoe, K.; Nishimura, N.; Sato, T. Analysis of beta-lactam antibiotics by high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry using bromoform. J. Pharm. Biomed. Anal. 2002, 30 (4), 1093−1102.

Chemicals (Text S1), instrumental settings of Cl-anion attachment APCI-QTOF-MS (Text S2), sample preparation (Text S3), pattern-reconstruction procedure (Text S4), QA/QC (Text S5), m/z values of [M + Br]− (Table S1), LODs and relative RFs (Table S2), quantification results using the Cl-anion attachment method (Table S3), SCCP CnClm compositions in environmental samples (Table S4), pattern-reconstruction results (Table S5), response-factor calculations (Figure S1), and mass spectrum deconvolution of MCCPs and LCCPs (Figure S2) (PDF)

AUTHOR INFORMATION

Corresponding Author

*Telephone: 0046 8 674 7315. Fax: 0046 8 674 7638. E-mail: [email protected]. ORCID

Bo Yuan: 0000-0002-2043-8128 Chang-Er L. Chen: 0000-0002-2069-4076 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Ulla Eriksson (ACES) is acknowledged for providing biota samples. The study was financially supported by the Swedish Research Council (VR 639-2013-6913) and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS 2017-01276).

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Determination of Chlorinated Paraffins by Bromide-Anion Attachment

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