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Compositional analysis of commercial oligomeric organophosphorus flame retardants used as alternatives for PBDEs: Concentrations and potential environmental emissions of oligomers and impurities Hidenori Matsukami, Go Suzuki, and Hidetaka Takigami Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b03447 • Publication Date (Web): 09 Oct 2015 Downloaded from http://pubs.acs.org on October 12, 2015

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Environmental Science & Technology

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Compositional analysis of commercial oligomeric organophosphorus flame

2

retardants used as alternatives for PBDEs: Concentrations and potential

3

environmental emissions of oligomers and impurities

4 5

Hidenori Matsukami,*,†,‡ Go Suzuki,† Hidetaka Takigami†,‡

6 7

†

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Environmental Studies (NIES), 16-2 Onogawa, Tsukuba 305-8506, Japan

9

‡

10

Center for Material Cycles and Waste Management Research, National Institute for

Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa

277-8563, Japan

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Corresponding author. Tel.: +81 29 850 2847; fax: +81 29 850 2759

13

E-mail address: [email protected] (H. Matsukami)

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1 ACS Paragon Plus Environment


16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

ABSTRACT Four commercial oligomeric organophosphorus flame retardants (o-PFRs) were characterized using a refractive index detector and atmospheric pressure photoionization (APPI)-quadrupole time-of-flight mass spectrometry (QTOF-MS) compatible with gel permeation chromatography (GPC). Commercial o-PFRs consisted of approximately 90% or more oligomers and several impurities. Triphenyl phosphate (TPHP), tris(dimethylphenyl) phosphate (TDMPP), tris(2chloroisopropyl) phosphate (TCIPP), and some new impurities were identified as byproducts in some manufacturing process of commercial o-PFRs for the first time. The concentrations of TPHP, TDMPP, and TCIPP were more than 1 weight%, whereas those of new impurities might be approximately 1 weight% by comparison among their abundances acquired through GPCAPPI-QTOFMS analysis. Based on their vapor pressure and water solubility estimations, the potential environmental emissions of low molecular weight impurities were expected to be higher than those of oligomers. The presence and environmental emissions of low molecular weight impurities might be regarded as risk factors along with commercial o-PFRs.


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TOC/Abstract PBDPP oligomers (n = 1–4) O O P O O

Impurities O O P O O

O O P O O

O O P O O

OH

PBDPP-IM1

n O O P O O

OH

PBDPP-IM2

O O P O O

PBDPP-IM3

TPHP

PBDPP-IM3 PBDPP-IM2 PBDPP-IM1 PBDPP-O1 (n=1) PBDPP-O2 (n=2) PBDPP-O3 (n=3) PBDPP-O4 (n=4)

35 36 37

4

6

8

min



38 39

INTRODUCTION

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During the past decade, commercial brominated flame retardants Penta-BDE and Octa-BDE

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for polymeric materials have been banned gradually worldwide.1 Deca-BDE has been gradually

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phased out along with them in many countries2 because of their persistence, bioaccumulation,

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and potentially toxic effects.3–6 Restrictions, regulations, and prohibitions against the production

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of commercial products of polybrominated diphenylethers (PBDEs) have engendered the

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increasing application of organophosphorus flame retardant (PFR) as an alternative to PBDEs.7

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Triphenyl phosphate (TPHP) has been used in engineering resins such as polyphenylene

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oxide/high impact polystyrene (PPO/HIPS) and polycarbonate/ABS (PC/ABS) blends. Some

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alkyl-substituted triaryl phosphates such as tris(methylphenyl) phosphate (TMPP) and

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tris(dimethylphenyl) phosphate (TDMPP) have been used in vinyl plastics. Some chlorinated

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trialkyl phosphates such as tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl)

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phosphate (TCIPP), and tris(1,3-dichloroisopropyl) phosphate (TDCIPP) have been used in

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polyurethane foam and textiles. Recently, emerging oligomeric organophosphorus flame

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retardants (o-PFRs) such as 1,3-phenylene bis(diphenyl phosphate) (PBDPP), bisphenol A

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bis(diphenyl phosphate) (BPA-BDPP), and 1,3-phenylene bis[di(2,6-dimethylphenyl) phosphate]

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(PBDMPP) have been used mainly for thermoplastics and thermosetting resins of PPO/HIPS and

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PC/ABS blends.8–11 Diethylene glycol bis[di(2-chloroisopropyl) phosphate] (DEG-BDCIPP) has

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been used mainly for flexible polyurethane forms. The chemical structures of o-PFRs are shown

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in Figure 1. Commercial o-PFRs are produced through oligomerization using raw materials

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including phosphorus oxychloride, diphenols, or diols, and phenols, alkylphenols, or chlorinated

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alcohols.12,13 Those products are known to contain their byproducts TPHP, TDMPP, and TCIPP

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with concentrations greater than 1 weight%. Information related to TPHP, TDMPP, and TCIPP 4 ACS Paragon Plus Environment

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is specified as impurities in the material safety data sheet (MSDS) and the patented processes for

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their manufacture.12,13

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Suzuki et al.14 reported an important case of ubiquitous contamination in indoor dust

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because of impurities in commercial products at concentrations of less than 1 weight%. Related

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information has not been specified in the MSDS for commercial products. These facts suggest

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that indoor sources of 2,4,6-tribromophenol (TBP), a potentially toxic compound in indoor dust,

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might account for impurities in some commercial brominated flame retardants (BFRs) currently

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used in household materials. Because TBP has not been used directly as a flame retardant, but

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rather as an intermediate for end-caps of those BFRs, such sources might be 1,2-bis(2,4,6-

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tribromophenoxy)ethane product (FF-680), TBBPA carbonate oligomer, TBP terminated product

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(BC-58), and brominated epoxy resin end-capped with tribromophenol product (F-3100). To

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elucidate the environmental and human health risks posed by commercial o-PFRs, information

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related to the concentrations and potential environmental emissions of the oligomers and

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impurities is crucially important. Nevertheless, no definitive information exists for commercial

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o-PFRs.

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This study was conducted to elucidate the concentrations and potential environmental

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emissions of the constituents in commercial o-PFRs, including PBDPP (product name CR-733S),

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BPA-BDPP (CR-741), PBDMPP (PX-200), and DEG-BDCIPP (CR-504L). First, the

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concentrations of the oligomers in commercial o-PFRs were calculated using a refractive index

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detector (RI) compatible with gel permeation chromatography (GPC). To identify the

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constituents, an atmospheric pressure photoionization (APPI)-quadrupole time-of-flight mass

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spectrometry (QTOF-MS) method compatible with GPC was then applied for structural

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composition investigations based on studies of their fragmentation behaviors. High mass



measurements

using

APPI-QTOF-MS

supported

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resolution

the

accuracy

of

their

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characterizations. Finally, the concentrations of impurities were quantified to discuss the

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potential environmental emissions of commercial o-PFRs.

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MATERIALS AND METHODS

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Reagents and samples. Stabilizer-free HPLC grade tetrahydrofuran (THF) was purchased

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from Wako Pure Chemical Industries Ltd. (Osaka, Japan). For the quantification of TPHP in CR-

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733S and CR-741, TDMPP in PX-200, and TCIPP in CR-504L, the reference substance of TPHP

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was purchased from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan), the reference substance

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of TDMPP was purchased from Hayashi Pure Chemical Inds. Ltd. (Osaka, Japan). The reference

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substance of TCIPP was purchased from Wako Pure Chemical Inds. Ltd. (Osaka, Japan). Each

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reference substance of TPHP, TDMPP, and TCIPP was dissolved with THF to a concentration of

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1 mg/mL and was diluted with THF to a concentration of 50 µg/mL. For quantification, each 50

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µg/mL reference solution was diluted to the five concentrations used to prepare a calibration

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curve: 10, 50, 200, 1000, and 5000 ng/mL. Commercial products of PBDPP (CR-733S), BPA-

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BDPP (CR-741), PBDMPP (PX-200), and DEG-BDCIPP (CR-504L) were obtained from

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Daihachi Chemical Industry Co. Ltd. (Osaka, Japan). For GPC-RI analysis, CR-733S, CR-741,

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PX-200, and CR-504L were dissolved respectively with THF to a concentration of 10 mg/mL.

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For GPC-APPI-QTOF-MS analysis, CR-733S, CR-741, PX-200, and CR-504L were dissolved

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respectively with THF to a concentration of 1 mg/mL and were diluted with THF to a

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concentration of 10 µg/mL. Chemical degradations of the constituents in THF were not

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confirmed in this study. A refrigerated autosampler set at 10 °C was used to maintain the

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stability of these diluted solutions during analyses.


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GPC-RI

analysis.

Conventional

separation

techniques

such

as

capillary

gas

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chromatography and reversed-phase liquid chromatography (LC) were incapable of

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comprehensive analysis of oligomeric and polymeric compounds. To elucidate the constituents

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in oligomeric and polymeric materials, GPC-RI analysis is the most commonly used method. In

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fact, GPC was able to separate all the molecules in the materials using mobile phase of the

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isocratic elution composition based on their hydrodynamic volumes where large molecules elute

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from the column before the smaller molecules.15,16 The RI device was able to detect all the

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molecules, but it cannot be used when running a gradient elution. An important benefit of using

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GPC-RI analysis was that we were able to characterize all the constituents in commercial o-PFRs.

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For this study, a Jasco RI-2031 plus detector compatible plus series device (Jasco LC-2000;

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Jasco Corp., Tokyo, Japan) was used for high-performance liquid chromatography. The

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constituents in CR-733S, CR-741, PX-200, and CR-504L were separated using a GPC column

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(250 mm × 4.6 mm i.d., KF-402HQ; Showa Denko K.K., Tokyo, Japan). The exclusion limit of

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polystyrene in KF-402HQ is 5000. The column temperature, flow rate of the mobile phase, and

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the injection volume were set, respectively, to 40 °C, 0.3 mL/min, and 2 µL. The content

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percentages of oligomers in CR-733S, CR-741, PX-200, and CR-504L were ascertained using

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area normalization based on the calculation of individual peak areas as a percentage of the total

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area of all the peaks acquired using GPC-RI analysis.

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GPC-APPI-QTOF-MS analysis. To obtain detailed compositional information from high

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mass accuracy and resolution measurement, QTOF-MS is a useful technique.17 High-resolution

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(normally 5000–10000 full width at half-maximum) can resolve constituents yielding ions, can



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reduce background interference, and can improve the detection accuracy. Actually, APPI has

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outperformed electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)

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from the viewpoints of ionization sensitivity of neutral compounds, minimal in-source

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fragmentation of thermally unstable compounds,18 and minimal matrix ionization suppression

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effects.19 Previous studies have demonstrated that THF is a suitable dopant for increasing

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ionization efficiency, especially when THF is used as the mobile phase or as an organic modifier

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in the mobile phase.20 Actually, GPC with a mobile phase composed of 100% THF that was

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compatible with on-line APPI-QTOF-MS detection was suitable for identification and

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quantification of the constituents in commercial o-PFRs.

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An ultrahigh performance liquid chromatography system equipped with a QTOF mass

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spectrometer was used with a QTOF LC/MS system (1290 Infinity/6530 Accurate-Mass; Agilent

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Technologies Inc., Santa Clara, CA, USA). The constituents in CR-733S, CR-741, PX-200, and

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CR-504L were separated using the GPC column used for GPC-RI analysis. The column

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temperature, flow rate of the mobile phase, and the injection volume were set, respectively, at

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40 °C, 0.3 mL/min, and 5 µL. The QTOF mass spectrometer was run in an APPI interface using

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positive and negative ion mode. Capillary voltages were set, respectively, to 3500 V for positive

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ion mode and to −3500 V for negative ion mode. The fragmentor was set to 150 V. The skimmer

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was set to 65 V. Nitrogen was used as the drying (350 °C, 5 l/min), vaporizer (300 °C), and

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nebulizer (50 psi) gas. Argon (>99.9999%; Japan Fine Products Co. Ltd., Kawasaki, Japan) was

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used as the collision gas. The mass range for the MS investigation of constituents was set at m/z

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100–3200. The mass range for MS/MS investigation was set to m/z 50–1500. As shown in Table

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S1 of Supporting Information, each different collision voltage for protonated molecule ion was

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set to obtain distinct fragmentation in this study.


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An APPI-QTOF-MS compatible GPC method was used to separate and detect the

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constituents in CR-733S, CR-741, PX-200, and CR-504L. Using APPI in positive ion mode, the

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available constituents yielded a protonated molecule, whereas a less abundant signal was

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obtained in negative ion mode. QTOF-MS detection resolved the protonated molecules of

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constituents and raised the detection accuracy. For identification of the constituents in CR-733S,

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CR-741, PX-200, and CR-504L, we conducted MS and MS/MS investigations using GPC-APPI-

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QTOF-MS. All available constituents were characterized from the elemental compositions of

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protonated molecule and fragment ions obtained from MS and MS/MS investigations. Based on

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results from the study of the fragmentation behaviors of oligomers, the chemical structures of the

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available impurities were elucidated. For the quantification of TPHP, TDMPP, and TCIPP, MS

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investigations were conducted using GPC-APPI-QTOF-MS. The extracted mass chromatograms

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(EIC) of protonated molecule ions of TPHP (m/z 327.0786), TDMPP (m/z 411.1725), and

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TCIPP (m/z 327.0087) with m/z widths of ±20 ppm were used for quantification. QTOF-MS

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accurate mass measurements supported those identifications. The accurate mass errors of those

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protonated molecules were less than 3.51 ppm. Using KF-402HQ column with a mobile phase

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composed of 100% THF in an isocratic mode, the retention times of TPHP, TDMPP, and TCIPP

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were found, respectively, to be 7.35 min, 7.55 min, and 7.46 min. TPHP, TDMPP, and TCIPP in

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the reference solutions were calibrated for the concentration range of 10–5000 ng/mL. Each

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calibration curve of TPHP, TDMPP, and TCIPP showed good linearity of more than 0.99 of

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correlation coefficients. Each quantitative value of TPHP, TDMPP, and TCIPP in triplicate

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experiments showed a good variation coefficient in the range of 0.9–6.6% (Table 1). The limits

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of quantification (LOQ) values of TPHP, TDMPP, and TCIPP were calculated using the signal-



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to-noise ratio (Table 2). The concentrations of TPHP, TDMPP, and TCIPP in procedural blanks

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were below the LOQ values.

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RESULTS AND DISCUSSION

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Characterization of oligomer and impurity in commercial o-PFRs. Table 1 presents

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elemental compositions and concentrations of oligomers and impurities in CR-733S and CR-741,

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PX-200, and CR-504L, as characterized using GPC-RI and GPC-APPI-QTOF-MS analyses. The

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application of a GPC column with a mobile phase composed of 100% THF in an isocratic mode

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separated the oligomers and impurities in CR-733S and CR-741, PX-200, and CR-504L. All

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constituents were eluted completely from the GPC column at retention times of 6.10–8.11 min.

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Detailed information for the identification of the oligomers and impurities based on the study of

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their fragmentation behaviors in MS/MS investigations is given in Supporting Information. The

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overlays of the chromatograms of the constituents in CR-733S, CR-741, PX-200, and CR-504L

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acquired using GPC-RI and GPC-APPI-QTOF-MS analyses are shown in Figures S1–S5 of

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Supporting Information. According to the results obtained from GPC-RI and GPC-APPI-QTOF-

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MS analyses, CR-733S consisted mainly of PBDPP oligomers including 71% dimer, 19% trimer,

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3.6% tetramer, and 0.57% pentamer, and 6.0% impurities including TPHP. Results show that

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CR-741 consisted mainly of BPA-BDPP oligomers including 88% dimer, 10% trimer, and

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0.66% tetramer, and 0.74% impurities including TPHP. PX-200 consisted mainly of PBDMPP

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oligomers including 96% dimer and 0.65% trimer, and 3.2% impurities including

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tris(dimethylphenyl) phosphate (TDMPP). CR-504L consisted mainly of DEG-BDCIPP

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oligomers including 64% dimer, 21% trimer, 6.5% tetramer, and 2.2% pentamer, and 6.3%

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impurities including tris(2-chloroisopropyl) phosphate (TCIPP). A previous report has described


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that the three major constituents in commercial PBDPP were 65–80% dimer, 15–30% trimer, and

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Compositional Analysis of Commercial Oligomeric ... - ACS Publications

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