Talanta 132 (2015) 635–640
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Talanta journal homepage: www.elsevier.com/locate/talanta
Raman spectroscopy based identification of flame retardants in consumer products using an acquired reference spectral library Sutapa Ghosal n, Huiting Fang Environmental Health Laboratory Branch, California Department of Public Health, Richmond, CA 94804, USA
art ic l e i nf o
a b s t r a c t
Article history: Received 10 September 2014 Received in revised form 1 October 2014 Accepted 4 October 2014
Flame retardants (FRs), a class of commonly used chemical additives in consumer products such as polyurethane foams, are well known for their persistence in the environment, bioaccumulation and potential toxicity [1]. In order to address the potential health concerns and environmental impacts associated with the wide-spread use these chemicals, it is essential to identify them efficiently in the environment and consumer products. Raman spectroscopy (RS) offers an attractive option for the noninvasive, in-situ identification of flame retardants in a variety of sample formats [2–4]. RS based chemical identification relies on the availability of spectral libraries for identification through spectral matching with reference chemicals. Here we present the application of Raman spectroscopy for identifying FR additives in select consumer products using an acquired spectral library of commonly used FRs. The RS based method described here enables simultaneous identification of multiple components within a sample, which can offer important insights into the sources of FR contamination, in addition to identification of the FR component itself. The availability of Raman spectral library of commercially used FRs, such as the one presented here, will facilitate the identification of these chemicals in consumer products. Published by Elsevier B.V.
Keywords: Raman spectroscopy Flame retardants Molecular identification
1. Introduction Since establishment of the Technical Bulletin in 1975 [5], by which the California Bureau of Electronic and Appliance Repair, Home Furnishings and Thermal Insulation (BHFTI) regulated the flammability of upholstered furniture and bedding products, a wide variety of flame-retardants (FR), especially brominated flameretardants (BFR), have been used by US manufacturers for decades to comply with the flammability standards outlined in the bulletin. Consequently, demand for FR chemicals in the US has increased by 4.6% each year, and is expected to reach 938 million pounds in 2016 according to the Global Information Inc. [6] At the same time, numerous studies have shown that the wide spread use of FRs is not safe as they pose potentially significant health risks [1]. As early as 1973, there were reports of adverse health effects resulting from the contamination of animal feed with polybrominated biphenyls (PBBs) in Michigan, and as a result PBBs were banned from production [7,8]. Over the last decade a number of widely used FRs including polybrominated diphenyl ethers (PBDE) such as penta- and octa-brominated diphenyl ethers (BDE), which are known for their toxicity effects [9], have either been banned by the state government n Corresponding author at: Environmental Health Laboratory Branch, California Department of Public Health, 850 Marina Bay Parkway, Mailstop G365/EHLB, Richmond, CA 94804, USA. Tel.: þ1 510 620 2815; fax: þ1 510 620 2825. E-mail address: [email protected] (S. Ghosal).
http://dx.doi.org/10.1016/j.talanta.2014.10.007 0039-9140/Published by Elsevier B.V.
or voluntarily phased out by US manufacturers. To further reduce US manufactures’ reliance on synthetic flame retardants, a new flammability standard TB117-2013 was issued recently by BHFTI [10]. TB117-2013 requires all upholstered furniture to pass a smolder resistant test rather than an open flame test [10]. In other words, US foam manufacturers are no longer required to add FR chemicals to pass the flammability test. Despite the restrictions on production and usage of toxic FRs, consumer products previously treated with banned chemicals are still in use. In addition, the proposed alternative FR species, such as tris(1,3-dichloro-2-propyl) phosphate (TDCPP), also pose significant environmental and health hazards [11]. As a result of these concerns, it has become necessary to monitor the prevalence and distribution of these chemicals in various consumer products and the environment in order to better understand and thus mitigate any associated health and environmental impacts. Numerous studies have been conducted to characterize flame retardants both in the environment and in consumer products using a variety of different techniques. Kierkegaard et al. identified decabromodiphenyl ethane, in sewage sludge, sediment, and indoor air using high-resolution mass spectrometry (MS) and quantified it with low-resolution MS [12]. Guardia et al. have reported a method for determining the concentration of PBDEs in multiple FR mixtures using gas chromatography/mass spectrometry (GC/MS) [13]. Stapleton et al. used GC/MS coupled with a portable X-ray fluorescence analyzer (XRF) to identity FR chemicals in polyurethane foam collected from baby products [14].
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While Webster et al. analyzed the presence of deca-BDE in indoor dust samples using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) as well as a micro-XRF [15]. MS based methods for the identification of FRs are not applicable for chemicals which are thermally labile, such as hexabromocyclododecane (HBCD) [16]. Moreover, MS based techniques often rely on invasive and time consuming sample preparation steps in order to provide molecular level information. Fluorescence and electron microscopy techniques offer elemental and morphological information, but lack FR specific molecular identification. Therefore, an analytical approach that offers direct, non-invasive molecular-level identification of FR chemicals in consumer products and in environmental samples with minimal sample preparation would be of considerable interest. Raman spectroscopy has been widely used as a non-invasive analytical tool for the characterization of both organic and inorganic materials since its inception in the 1930s [17]. The molecular specificity of Raman analysis can be combined with high spatial resolution afforded by a microscopy platform and the resulting technique is referred to as Raman micro-spectroscopy (RMS), which is a highly versatile tool for a broad range of analytical applications. In particular, access to spatially resolved chemical information without extensive sample preparation or water interference makes the RMS technique appropriate for a variety of sample formats [17,18]. We have previously demonstrated the application of RMS for identifying individual fungal spores [19] as well as FR species in environmental samples [2,3]. Kikuchi et al used Raman spectroscopy for the analysis of brominated FRs in electrical and electronic equipment [4]. Raman spectroscopy based chemical identification involves qualitative/quantitative spectral matching of an unknown spectrum with a spectral library of reference chemicals, and hence relies on the availability of welldocumented spectral libraries. Raman spectral libraries related to various applications have been created in order to facilitate the increasing use of Raman spectroscopy in a variety of fields including forensic science, archaeology, art, medicine, solid-state physics, and pharmaceutical chemistry. Given the suitability of RMS for environmental analysis, it is necessary to create tailored spectral libraries for particular applications such as the detection/ identification of specific environmental contaminants. Here we present the acquisition of Raman spectral library of FR chemicals commonly used in consumer products. The acquired spectral library is subsequently used to identify of FR additives in representative consumer items. This study illustrates the application of Raman spectroscopy for the identification of FR additives and polymer matrices associated with consumer products through the matching of unique spectral signatures. Simultaneous identification of FR with the associated polymer matrix is essential for linking FR contaminants to specific consumer materials, which is an important step towards source attribution. Creation of a reference spectral library for commonly used FRs is essential for the RS based identification of FRs in a broad range of samples.
2. Material and methods 2.1. FR materials FR reference chemicals for the creation of FR specific spectral library were acquired from various commercial sources. These include Sigma-Aldrich, St-Louis, MO; Pfaltz and Bauer, Waterbury, CT, and AccuStandard, New Haven, CT. The various FR species analysed in this study are—decabromodiphenyl ether (deca-BDE,); hexabromodiphenyl ether (hexa-BDE); 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB); bis(2-ethylhexyl)-tetrabromophthalate (TBPH); tris(1,3dichloro-;2-propyl) phosphate (TDCPP); tris(2-chloroethyl)
phosphate (TCEP); hexabromocyclododecane (HBCDD); tetrabrom obisphenol A (TBBPA); brominated polystyrene (Br-PS); tris(2-chloropropyl) phosphate (TCPP); triphenyl phosphate (TPP) and antimony trioxide (Sb2O3). Reference spectrum of pentabromodiphenyl ether (penta BDE) was acquired from polyurethane foam containing 5.3% Penta-BDE as measured by bulk GC–MS [20] and was validated by comparison with penta-BDE spectrum available in the literature [21]. Melamine spectrum was available from in-house Raman spectral libraries. 2.2. Consumer materials Representative consumer materials for this study were collected from commonly used consumer items, which are typically known to contain FRs. These included materials from a VCR and a computer monitor (CRT) casings as well as the fabric from a car visor. The exact manufacture dates of these items were not known, but they were estimated to have originated between the years of 1985–2005 and had been subjected to extensive use. Additional consumer materials included several samples of polyurethane foam (PUF)—these samples were kindly provided by Dr. Thomas Webster (Boston University) and Dr. Heather Stapleton (Duke University) and had been collected as part of their study on FR exposure among gymnasts [20]. Approximately 1 mm2 sized samples were extracted from each material using a clean scalpel blade. The samples were then placed on double-sided adhesive carbon substrates mounted on standard aluminum SEM stubs. 2.3. Confocal Raman spectroscopy Raman spectroscopy measurements were performed using two commercially available micro-Raman setups, each equipped with a near-infrared 785 nm diode laser—(1) Senterra Dispersive Raman microscope (Bruker Optics Inc., Billerica, MA), and (2) Renishaw inVia Raman microscope (Renishaw Plc., Old Town, Wotton-underEdge, Gloucestershire, U. K.). On the Senterra Raman microscope, all spectra were recorded and analyzed using OPUS 6.0.72 dll 3.0.1.1 software (Opus Software Inc., San Rafael, CA) with a spectral resolution of 3–5 cm 1. The Senterra system is equipped with Sure_Cals function for continuous automated laser and Raman frequency calibration using an integrated neon laser light. On the Renishaw system, GRAMS WiRE software package (Galactic Industries Corp., 395 Main St., Salem, NH) was used for instrument control and data acquisition. The spectral resolution was 2.5 cm 1. Wavelength calibration was performed periodically using neon laser light. On both systems a silicon wafer spectrum was acquired on a daily basis as a quality control step to monitor and correct for minor wavelength offsets. Samples were excited using 1–100 mW of 785 nm laser light focused onto the sample typically through a 20 or 50 objective. Signal acquisition times varied between 60 and 120 s per measurement. Spectra for the liquid FR samples were acquired using a Macrokit (Renishaw Plc) sample holder coupled to the Renishaw microscope, which enables spectral acquisition in the liquid phase. Raw spectra were processed to eliminate dark noise and contributions from the spectrometer’s optical parts. The spectra were baseline corrected using a Fixed Multi-point Baseline Correction algorithm (GRAMS/AI version 9.1) or a Concave Rubberband Correction method (Opus Software Inc., San Rafael, CA) and smoothed using Savtisky–Golay smoothing algorithm (GRAMS/AI version 9.1). Preprocessed spectra of the reference FR samples were compiled into a spectral database using the GRAMS Spectral ID software from Thermo Fisher Scientific Informatics. Molecular identification of sample composition was accomplished through spectral library searches using both commercial and laboratory acquired Raman spectral libraries. Spectral library searches were performed using
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an automated correlation based search algorithm (GRAMS Spectral ID, version 9.1). The quality of the match between the sample and the various library spectra was evaluated based on visual inspection of the spectra as well as calculated Hit Quality Index (HQI) values, which ranged from 0 to 1, with 0 representing a perfect match.
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spectral analysis for distinguishing between broad classes of FRs such as BFR versus chlorinated PFR, as well as identifying individual FR species. This will be illustrated in greater detail in subsequent sections, where we present the identification of FR additives in representative consumer products.
3.2. Identification of FR additives in polyurethane foam 3. Results and discussion 3.1. Acquisition of FR spectral library In order to identify an unknown chemical through spectral library search it is necessary to use a reference spectral library of relevant chemicals against which the unknown spectrum can be evaluated for a potential match. Fig. 1 shows the acquired Raman spectra of a number of FR reference chemicals commonly found in consumer products. The spectral range shown in Fig. 1 extends from 100 to 2000 cm 1, where majority of the FR related spectral features are typically located. Each FR species displays a unique spectral fingerprint, which distinguishes it from other members of the FR family and can be used to identify it. This is true even for closely related FRs such as PBDEs, which differ in terms of the number and arrangement of Br ions per molecule. For example, hexa- and deca-BDE (containing 6 and 10 Br ions, respectively) both have peaks in the 100–250 cm 1 region (Fig. 1), typically associated with brominated FRs [22]. However, each can be individually identified based on their unique spectral features. Deca-BDE is characterized by triplet peaks centered at 224 cm 1, while hexa-BDE has a broad peak at 212 cm 1. In both cases, the general peak position is indicative of the C-Br bond [22], but the detailed features are representative of their unique molecular structure. Spectral feature corresponds to distinct molecular vibrations and as such are characteristic of the analyte’s unique molecular and structural composition. Since the ban on use of various BFRs, phosphorus based flame retardants (PFRs) have often been proposed as potential alternatives. PFRs can be broadly classified into three groups i.e. inorganic, organic and halogen containing PFRs [23]. Raman spectra of some of the commonly used PFRs are shown in Fig. 1. The three chlorine containing PFRs (TCEP, TCPP, TDCPP) all show prominent peaks in the 600–800 cm 1 region typically associated with C–Cl stretching [22]. As with BFRs, the individual PFR species are clearly distinguishable based on their unique spectral signatures. The acquired FR spectral library, shown in Fig. 1, highlights the utility of Raman
Polyurethane foam is one of the most extensively used polymer materials, with widespread applications in furniture and a variety of other consumer products. The widespread use of PUF makes it potentially a significant source of PUF related FR contamination in the environment. In recent years, Stapleton et al and Carignan et al. have investigated this particular class of FRs in terms of their presence in consumer products and the environment [14,20]. Here we present RMS based identification of FRs in PUF samples that have been previously characterized by Carignan et al. using gas chromatography negative chemical ionization mass spectrometry (GC/ECNIMS) and X-ray fluorescence spectroscopy (XRF) [20]. Given the detailed analytical information already available about these samples, they represent a unique opportunity for exploring the feasibility of RMS based identification of FRs in consumer products. Table 1 lists the PUF samples examined in this study along with the associated FRs and their respective concentrations as reported by Carignan et al. [20]. Carignan et al. identified TDCPP to be the primary FR in PUFs 7 and 8, with measured concentrations of 6.6% and 5.6%, respectively [20]. RMS analysis of PUFs 7 and 8 is shown in Fig. 2 along with the reference spectra for melamine and TDCPP. Melamine was identified as a major constituent in both PUF 7 and 8 based on spectral matching analyses. Melamine and its derivatives are classified as non-halogenated flame retardants and have been proposed as viable alternatives to Penta-BDE [23–25]. It is currently used in flexible polyurethane foam in concentration ranging from 30% to 40% melamine per weight of the polyol and is typically applied as a crystalline powder [25]. Strong melamine specific peaks (967.3 cm 1, 984 cm 1) evident in PUF 7 and 8 spectra suggest significant presence of melamine in the foams. This is consistent with the typical concentrations of melamine reported in the literature (30‐40%) [25], which is considerably higher than the TDCPP concentrations (o10%) reported by Carignan et al. [20]. In addition to melamine, PUF 7 spectrum also showed evidence of TDCPP along with peaks related to the polymer matrix (600–1800 cm 1) (Fig. 3). Polymer related peaks representing the PUF matrix were common to all the PUF samples examined in this study. The two individual PUF 7 spectra shown in Figs. 2 and 3 were acquired at two different locations on the sample and are spectrally distinct. The observed differences in spectral features correspond to differences in molecular composition at these two sites and as such are indicative of spatial heterogeneity in sample composition. The PUF 7 spectrum shown in Fig. 2 is characterized by strong melamine peaks suggestive of a melamine hotspot. The observed heterogeneous distribution of melamine in PUF 7 is Table 1 List of PUF samples analyzed in this study along with the FR species and the corresponding concentrations as reported by Carignan et al. [20].
Fig. 1. Reference Raman spectra of FRs commonly present in consumer products.
PUF
FRs (%)20
7 8 6 5 4 3
TDCPP (6.6) TDCPP (5.6) TBB (2.8), TPP (1.1), TBPH (1.3) Penta BDE (3.7), TPP (0.3) Penta BDE (5.3), TPP (0.4) Penta BDE (4.8), TPP (0.3), TDCPP (0.1)
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Fig. 2. RMS analyses of two different foam samples (PUF 7 and 8) showing spectral comparison with reference Raman spectra of melamine and tris(1,3-dichloro-2propyl) phosphate (TDCPP).
Fig. 3. Raman spectrum of the PUF 7 foam sample showing spectral matches with reference Raman spectra of tris(1,3-dichloro-2-propyl) phosphate (TDCPP), melamine, polyurethane foam (PUF). The red dotted lines identify position of the strongest TDCPP peaks.
consistent with the application of melamine as crystalline powder, which can create localized hotspots. A particular advantage of RMS analysis is that it enables simultaneous identification of multiple constituents in the sample by probing the entire Raman active compositional profile. For instance, in case of PUF 7, we were able to identify several components including melamine, TDCPP and the polymer matrix based on the acquired spectrum. In Raman analysis, spectral response is determined by concentration and Raman crosssection of the constituent molecular bonds. Therefore, the spectral response can be dominated by signals from constituents with higher concentration and/or Raman cross-section. An example of this can be seen in case of PUF 6, which was reported as containing multiple FR species—TPP, TBB and TBPH [20]. Fig. 4 shows acquired spectrum of PUF 6 along with reference spectra of the three constituent FR species. The PUF 6 spectrum is dominated by peaks arising from the polymer matrix, which is the primary constituent. In comparison, the FR related peaks are less prominent. TPP is identifiable based on two sharp peaks located at 1005 cm 1 (P–O–C anti-symmetric stretch in organ-ophosphorus compounds) and 3063 cm 1 (¼C–H stretch of the benzene ring) [22]. TBB and TBPH
Fig. 4. Raman spectrum of the PUF 6 foam sample showing spectral matches with reference Raman spectra of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), bis(2ethylhexyl)-tetrabromophthalate (TBPH), triphenyl phosphate (TPP). Dotted green, purple and red lines identify positions of the strongest peaks for TBB, TBPH and TPP, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
both show a sharp peak around 216 cm 1, indicative of the C-Br bond [22]. In addition to the 216 cm 1 band, TBB also has a sharp peak at 1555 cm 1 (benzene ring stretch), which distinguishes it from TBPH [22]. All of these FR related peaks are evident in the PUF 6 spectrum though they are less prominent compared to the PUF peaks. In addition to the above mentioned FR species, PUF 6 also showed some localized presence of melamine. The three remaining PUF samples (PUF 3, 4, and 5) were all reported as containing TPP and Penta-BDE in varying concentrations, Penta-BDE being the dominant FR species [20]. Fig. 5 shows acquired spectra of the three PUF samples. All three spectra have a sharp peak at 1005 cm 1 from TPP. They also contain singlet and doublet peaks in the 100–250 cm 1 region, which are characteristic of penta BDE [21]. Similar to PUF 6, these spectra also show strong response from the polymer matrix. In summary, RMS analysis of the PUF samples confirmed the presence of FR species previously identified by Carignan et al [20]. In addition, RMS analyses also identified the presence of melamine, not reported by Carignan et al [20]. These results also illustrate the simultaneous identification of multiple constituents in a sample, which is a particularly advantageous in terms of contaminant and source attribution in environmental monitoring. This is discussed further in the following section where we present RMS based characterization of select consumer products, simultaneously identifying both the polymer matrix and the associated FR species. 3.3. Identification of FR species and polymer matrices in consumer products Consumer products are a major source of FR related contamination, particularly in indoor environments [15,26–29] where migration of FRs from consumer items into the surroundings can take place via volatilization and/or physical weathering of products [15,30,31]. Several studies have highlighted the necessity of linking FR contaminants in the environment to their original sources [15,26]. In case of mechanical transfer of FRs via physical weathering of products, FR chemicals are often transferred in association with the product matrix. We have previously reported the identification of FRs together with the associated polymer matrix, in residential dust samples, which is suggestive of
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Fig. 5. RMS analyses of foam samples from three different sources with peak assignments for the identified FR species, penta BDE and triphenyl phosphate (TPP). Dotted red and green lines identify positions of the strongest peaks for penta BDE and TPP, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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mechanical transfer of FRs from consumer items into the environment via physical weathering [2,3]. Linking FR contamination to a specific consumer item necessitates knowledge of the product composition i.e. FR species and polymer matrix associated with the item. As mentioned earlier, Raman spectroscopy is well suited for this type of multicomponent analysis. To illustrate this point, we present RMS based characterization of three consumer items (car visor covering and, casing materials from a VCR and a computer monitor) with the goal of identifying the polymer matrices and the associated FR species. Fig. 6 shows acquired spectra of the three consumer materials along with reference spectra of the polymer and FR constituents identified through spectral library search. In all three cases, both the polymer matrix and the associated FR species are readily identifiable based on their unique spectral signatures. The car visor material consists of two FRs, deca-BDE and antimony trioxide, incorporated into a polyvinyl chloride (PVC) polymer matrix (Fig. 6a). The VCR casing material was identified as high-impact polystyrene (HIPS) with deca-BDE as the FR component (Fig. 6b). The polymer and FR components of the CRT casing were determined to be polycarbonate (PC) and TPP, respectively (Fig. 6c). Product specific spectral fingerprints offered by the RMS method
Fig. 6. RMS analyses of consumer products. (a) Raman spectrum of car visor material showing spectral match with reference Raman spectra deca-BDE, antimony trioxide (Sb2O3) and polyvinyl chloride (PVC). (b) Raman spectrum of the VCR casing showing spectral match with reference Raman spectra of high impact polystyrene (HIPS) and deca-BDE. (c) Raman spectrum of the CRT casing showing spectral match with reference Raman spectra of poly carbonate (PC) and triphenyl phosphate (TPP). Insets: 50 reflected light image showing the region of RMS analysis.
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described here can be used for FR identification and source attribution in a variety of environmental samples and consumer products. 4. Conclusion The results presented here highlight the utility of Raman spectroscopy as a non-invasive analytical tool for the identification and source attribution of FRs in consumer products and environmental samples. RS based identification relies on the availability of relevant spectral libraries of reference chemicals in order to accomplish chemical identification through spectral matching. We have compiled a reference spectral library of several commonly used FR chemicals to facilitate the identification process. The acquired spectral library has been used successfully to identify FR additives in a selection of commercially used polyurethane foam samples. The foam samples had been previously characterized by GC–MS as part of a separate study [20]. Our results are in excellent agreement with the previous study and also offer additional information such as the presence of melamine, another FR species. We have also identified polymer matrices and FR species associated with three commonly used consumer items to illustrate the applicability of RS for source characterization. Acknowledgements S.G. and H.F. would like to thank Dr. Thomas Webster (Boston University) and Dr. Heather Stapleton (Duke University) for access to the PUF samples. S.G. would also like to thank Dr. Jeff Wagner (CDPH) for access to consumer product samples and Dr. Simon Ip for helpful discussions. References [1] S.D. Shaw, et al., Rev. Environ. Health 25 (4) (2010) 261–305. [2] S. Ghosal, J. Wagner, Analyst (2013) 3836–3844138 (2013) 3836–3844.
[3] Wagner, J., et al., Morphology, Spatial Distribution, and Concentration of Flame Retardants in Consumer Products and Environmental Dusts using Scanning Electron Microscopy and Raman Micro-spectroscopy. 2012. [4] S. Kikuchi, et al., Anal. Sci. 20 (2004) 1111–1112. [5] California Bureau of Electronic and Appliance Repair, H.F.a.T.I., Requirements, Test Procedure and Apparatus for Testing the Flame Retardance of Resilient Filling Materials Used in Upholstered Furniture., in Technical Bulletin 117 S.o.C. D.o.C. Affairs, (Ed.), 1975: Sacramento, CA. [6] Information, G., Flame Retardants (US Market & Forecast), in Advanced Material Market Research Report. 2012, Global Information p. 245. [7] J.K. Stross, et al., Toxicol. Appl. Pharmacol. 58 (1981) 145–150. [8] J. Jacobson, et al., Am. J. Public Health 74 (4) (1984) 378–379. [9] T.A. McDonald, Chemosphere 46 (5) (2002) 745–755. [10] California Bureau of Electronic and Appliance Repair, H.F.a.T.I., Requirements, Test Procedure and Apparatus for Testing the Flame Retardance of Resilient Filling Materials Used in Upholstered Furniture., S.o.C.D.o.C. Affairs, (Ed.), 2013: Sacramento, CA. [11] I. van der Veen, J. de Boer, Chemosphere (2012) (Journal Article). [12] A. Kierkegaard, J. Bjorklund, U. Friden, Environ. Sci. Technol. 38 (12) (2004) 3247–3253. [13] M.J. Guardia, R.C. Hale, E. Harvey, Environ. Sci. Technol. 40 (2006) 6247–6254. [14] H.M. Stapleton, et al., Environ. Sci. Technol. 45 (2011) 5323–5331. [15] T.F. Webster, et al., Environ. Sci. Technol. 43 (9) (2009) 3067–3072. [16] E. Eljarrat, D. Barceló, TrAC Trends Anal. Chem. 23 (10) (2004) 727–736. [17] M.J. Pelletier, Analytical Applications of Raman Spectroscopy, Blackwell Science Ltd., Oxford, 1999. [18] G.J. Puppels, et al., J. Raman Spectrosc. 22 (1991) 217–225. [19] S. Ghosal, J.M. Macher, K. Ahmed, Environ. Sci. Technol. 46 (11) (2012) 6088–6095. [20] C.C. Carignan, et al., Environ. Sci. Technol. 47 (23) (2013) 13848–13856. [21] G.C. Stevens, et al., A new rapid analysis method for fire retardants in polymers, in: InterFlam, Interscience Communications: University of Nottingham, Nottingham, UK, 2010. [22] J.B. Lambert, H.F. Shurvell, R.G. Cooks, Introduction to Organic Spectroscopy, Macmillan, New York, 1987. [23] I. van der Veen, J. de Boer, Chemosphere 88 (2012) 1119–1153. [24] S.L. Waaijers, et al., Rev. Environ. Contam. Toxicol. 222 (2013) 1–71. [25] U.S.E.P. Agency, Environmental Profiles of Chemical Flame-Retardant Alternatives for Low-Density Polyurethane Foam, U.S.E.P. Agency, 2005. [26] J.G. Allen, et al., Environ. Sci. Technol. 42 (11) (2008) 4222–4228. [27] Suzuki, G., et al., PBDEs and PBDD/Fs in House and Office Dust from Japan., in Organohalogen Compounds. 2006: Oslo, Norway. p. 1843–1846. [28] H.M. Stapleton, et al., Environ. Sci. Technol. 39 (4) (2005) 925–931. [29] S. Hazrati, S. Harrad, Environ. Sci. Technol. 40 (24) (2006) 7584. [30] Kose, T., et al., Determination of the Emission Amount of Organic Pollutants from Household Products Using a Model Room., in Organohalogen Compounds. 2008: Birmingham, England. p. 2305–2308. [31] G. Suzuki, et al., Environ. Sci. Technol. 43 (5) (2009) 1437–1442.
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Talanta journal homepage: www.elsevier.com/locate/talanta
Raman spectroscopy based identification of flame retardants in consumer products using an acquired reference spectral library Sutapa Ghosal n, Huiting Fang Environmental Health Laboratory Branch, California Department of Public Health, Richmond, CA 94804, USA
art ic l e i nf o
a b s t r a c t
Article history: Received 10 September 2014 Received in revised form 1 October 2014 Accepted 4 October 2014
Flame retardants (FRs), a class of commonly used chemical additives in consumer products such as polyurethane foams, are well known for their persistence in the environment, bioaccumulation and potential toxicity [1]. In order to address the potential health concerns and environmental impacts associated with the wide-spread use these chemicals, it is essential to identify them efficiently in the environment and consumer products. Raman spectroscopy (RS) offers an attractive option for the noninvasive, in-situ identification of flame retardants in a variety of sample formats [2–4]. RS based chemical identification relies on the availability of spectral libraries for identification through spectral matching with reference chemicals. Here we present the application of Raman spectroscopy for identifying FR additives in select consumer products using an acquired spectral library of commonly used FRs. The RS based method described here enables simultaneous identification of multiple components within a sample, which can offer important insights into the sources of FR contamination, in addition to identification of the FR component itself. The availability of Raman spectral library of commercially used FRs, such as the one presented here, will facilitate the identification of these chemicals in consumer products. Published by Elsevier B.V.
Keywords: Raman spectroscopy Flame retardants Molecular identification
1. Introduction Since establishment of the Technical Bulletin in 1975 [5], by which the California Bureau of Electronic and Appliance Repair, Home Furnishings and Thermal Insulation (BHFTI) regulated the flammability of upholstered furniture and bedding products, a wide variety of flame-retardants (FR), especially brominated flameretardants (BFR), have been used by US manufacturers for decades to comply with the flammability standards outlined in the bulletin. Consequently, demand for FR chemicals in the US has increased by 4.6% each year, and is expected to reach 938 million pounds in 2016 according to the Global Information Inc. [6] At the same time, numerous studies have shown that the wide spread use of FRs is not safe as they pose potentially significant health risks [1]. As early as 1973, there were reports of adverse health effects resulting from the contamination of animal feed with polybrominated biphenyls (PBBs) in Michigan, and as a result PBBs were banned from production [7,8]. Over the last decade a number of widely used FRs including polybrominated diphenyl ethers (PBDE) such as penta- and octa-brominated diphenyl ethers (BDE), which are known for their toxicity effects [9], have either been banned by the state government n Corresponding author at: Environmental Health Laboratory Branch, California Department of Public Health, 850 Marina Bay Parkway, Mailstop G365/EHLB, Richmond, CA 94804, USA. Tel.: þ1 510 620 2815; fax: þ1 510 620 2825. E-mail address: [email protected] (S. Ghosal).
http://dx.doi.org/10.1016/j.talanta.2014.10.007 0039-9140/Published by Elsevier B.V.
or voluntarily phased out by US manufacturers. To further reduce US manufactures’ reliance on synthetic flame retardants, a new flammability standard TB117-2013 was issued recently by BHFTI [10]. TB117-2013 requires all upholstered furniture to pass a smolder resistant test rather than an open flame test [10]. In other words, US foam manufacturers are no longer required to add FR chemicals to pass the flammability test. Despite the restrictions on production and usage of toxic FRs, consumer products previously treated with banned chemicals are still in use. In addition, the proposed alternative FR species, such as tris(1,3-dichloro-2-propyl) phosphate (TDCPP), also pose significant environmental and health hazards [11]. As a result of these concerns, it has become necessary to monitor the prevalence and distribution of these chemicals in various consumer products and the environment in order to better understand and thus mitigate any associated health and environmental impacts. Numerous studies have been conducted to characterize flame retardants both in the environment and in consumer products using a variety of different techniques. Kierkegaard et al. identified decabromodiphenyl ethane, in sewage sludge, sediment, and indoor air using high-resolution mass spectrometry (MS) and quantified it with low-resolution MS [12]. Guardia et al. have reported a method for determining the concentration of PBDEs in multiple FR mixtures using gas chromatography/mass spectrometry (GC/MS) [13]. Stapleton et al. used GC/MS coupled with a portable X-ray fluorescence analyzer (XRF) to identity FR chemicals in polyurethane foam collected from baby products [14].
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While Webster et al. analyzed the presence of deca-BDE in indoor dust samples using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) as well as a micro-XRF [15]. MS based methods for the identification of FRs are not applicable for chemicals which are thermally labile, such as hexabromocyclododecane (HBCD) [16]. Moreover, MS based techniques often rely on invasive and time consuming sample preparation steps in order to provide molecular level information. Fluorescence and electron microscopy techniques offer elemental and morphological information, but lack FR specific molecular identification. Therefore, an analytical approach that offers direct, non-invasive molecular-level identification of FR chemicals in consumer products and in environmental samples with minimal sample preparation would be of considerable interest. Raman spectroscopy has been widely used as a non-invasive analytical tool for the characterization of both organic and inorganic materials since its inception in the 1930s [17]. The molecular specificity of Raman analysis can be combined with high spatial resolution afforded by a microscopy platform and the resulting technique is referred to as Raman micro-spectroscopy (RMS), which is a highly versatile tool for a broad range of analytical applications. In particular, access to spatially resolved chemical information without extensive sample preparation or water interference makes the RMS technique appropriate for a variety of sample formats [17,18]. We have previously demonstrated the application of RMS for identifying individual fungal spores [19] as well as FR species in environmental samples [2,3]. Kikuchi et al used Raman spectroscopy for the analysis of brominated FRs in electrical and electronic equipment [4]. Raman spectroscopy based chemical identification involves qualitative/quantitative spectral matching of an unknown spectrum with a spectral library of reference chemicals, and hence relies on the availability of welldocumented spectral libraries. Raman spectral libraries related to various applications have been created in order to facilitate the increasing use of Raman spectroscopy in a variety of fields including forensic science, archaeology, art, medicine, solid-state physics, and pharmaceutical chemistry. Given the suitability of RMS for environmental analysis, it is necessary to create tailored spectral libraries for particular applications such as the detection/ identification of specific environmental contaminants. Here we present the acquisition of Raman spectral library of FR chemicals commonly used in consumer products. The acquired spectral library is subsequently used to identify of FR additives in representative consumer items. This study illustrates the application of Raman spectroscopy for the identification of FR additives and polymer matrices associated with consumer products through the matching of unique spectral signatures. Simultaneous identification of FR with the associated polymer matrix is essential for linking FR contaminants to specific consumer materials, which is an important step towards source attribution. Creation of a reference spectral library for commonly used FRs is essential for the RS based identification of FRs in a broad range of samples.
2. Material and methods 2.1. FR materials FR reference chemicals for the creation of FR specific spectral library were acquired from various commercial sources. These include Sigma-Aldrich, St-Louis, MO; Pfaltz and Bauer, Waterbury, CT, and AccuStandard, New Haven, CT. The various FR species analysed in this study are—decabromodiphenyl ether (deca-BDE,); hexabromodiphenyl ether (hexa-BDE); 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB); bis(2-ethylhexyl)-tetrabromophthalate (TBPH); tris(1,3dichloro-;2-propyl) phosphate (TDCPP); tris(2-chloroethyl)
phosphate (TCEP); hexabromocyclododecane (HBCDD); tetrabrom obisphenol A (TBBPA); brominated polystyrene (Br-PS); tris(2-chloropropyl) phosphate (TCPP); triphenyl phosphate (TPP) and antimony trioxide (Sb2O3). Reference spectrum of pentabromodiphenyl ether (penta BDE) was acquired from polyurethane foam containing 5.3% Penta-BDE as measured by bulk GC–MS [20] and was validated by comparison with penta-BDE spectrum available in the literature [21]. Melamine spectrum was available from in-house Raman spectral libraries. 2.2. Consumer materials Representative consumer materials for this study were collected from commonly used consumer items, which are typically known to contain FRs. These included materials from a VCR and a computer monitor (CRT) casings as well as the fabric from a car visor. The exact manufacture dates of these items were not known, but they were estimated to have originated between the years of 1985–2005 and had been subjected to extensive use. Additional consumer materials included several samples of polyurethane foam (PUF)—these samples were kindly provided by Dr. Thomas Webster (Boston University) and Dr. Heather Stapleton (Duke University) and had been collected as part of their study on FR exposure among gymnasts [20]. Approximately 1 mm2 sized samples were extracted from each material using a clean scalpel blade. The samples were then placed on double-sided adhesive carbon substrates mounted on standard aluminum SEM stubs. 2.3. Confocal Raman spectroscopy Raman spectroscopy measurements were performed using two commercially available micro-Raman setups, each equipped with a near-infrared 785 nm diode laser—(1) Senterra Dispersive Raman microscope (Bruker Optics Inc., Billerica, MA), and (2) Renishaw inVia Raman microscope (Renishaw Plc., Old Town, Wotton-underEdge, Gloucestershire, U. K.). On the Senterra Raman microscope, all spectra were recorded and analyzed using OPUS 6.0.72 dll 3.0.1.1 software (Opus Software Inc., San Rafael, CA) with a spectral resolution of 3–5 cm 1. The Senterra system is equipped with Sure_Cals function for continuous automated laser and Raman frequency calibration using an integrated neon laser light. On the Renishaw system, GRAMS WiRE software package (Galactic Industries Corp., 395 Main St., Salem, NH) was used for instrument control and data acquisition. The spectral resolution was 2.5 cm 1. Wavelength calibration was performed periodically using neon laser light. On both systems a silicon wafer spectrum was acquired on a daily basis as a quality control step to monitor and correct for minor wavelength offsets. Samples were excited using 1–100 mW of 785 nm laser light focused onto the sample typically through a 20 or 50 objective. Signal acquisition times varied between 60 and 120 s per measurement. Spectra for the liquid FR samples were acquired using a Macrokit (Renishaw Plc) sample holder coupled to the Renishaw microscope, which enables spectral acquisition in the liquid phase. Raw spectra were processed to eliminate dark noise and contributions from the spectrometer’s optical parts. The spectra were baseline corrected using a Fixed Multi-point Baseline Correction algorithm (GRAMS/AI version 9.1) or a Concave Rubberband Correction method (Opus Software Inc., San Rafael, CA) and smoothed using Savtisky–Golay smoothing algorithm (GRAMS/AI version 9.1). Preprocessed spectra of the reference FR samples were compiled into a spectral database using the GRAMS Spectral ID software from Thermo Fisher Scientific Informatics. Molecular identification of sample composition was accomplished through spectral library searches using both commercial and laboratory acquired Raman spectral libraries. Spectral library searches were performed using
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an automated correlation based search algorithm (GRAMS Spectral ID, version 9.1). The quality of the match between the sample and the various library spectra was evaluated based on visual inspection of the spectra as well as calculated Hit Quality Index (HQI) values, which ranged from 0 to 1, with 0 representing a perfect match.
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spectral analysis for distinguishing between broad classes of FRs such as BFR versus chlorinated PFR, as well as identifying individual FR species. This will be illustrated in greater detail in subsequent sections, where we present the identification of FR additives in representative consumer products.
3.2. Identification of FR additives in polyurethane foam 3. Results and discussion 3.1. Acquisition of FR spectral library In order to identify an unknown chemical through spectral library search it is necessary to use a reference spectral library of relevant chemicals against which the unknown spectrum can be evaluated for a potential match. Fig. 1 shows the acquired Raman spectra of a number of FR reference chemicals commonly found in consumer products. The spectral range shown in Fig. 1 extends from 100 to 2000 cm 1, where majority of the FR related spectral features are typically located. Each FR species displays a unique spectral fingerprint, which distinguishes it from other members of the FR family and can be used to identify it. This is true even for closely related FRs such as PBDEs, which differ in terms of the number and arrangement of Br ions per molecule. For example, hexa- and deca-BDE (containing 6 and 10 Br ions, respectively) both have peaks in the 100–250 cm 1 region (Fig. 1), typically associated with brominated FRs [22]. However, each can be individually identified based on their unique spectral features. Deca-BDE is characterized by triplet peaks centered at 224 cm 1, while hexa-BDE has a broad peak at 212 cm 1. In both cases, the general peak position is indicative of the C-Br bond [22], but the detailed features are representative of their unique molecular structure. Spectral feature corresponds to distinct molecular vibrations and as such are characteristic of the analyte’s unique molecular and structural composition. Since the ban on use of various BFRs, phosphorus based flame retardants (PFRs) have often been proposed as potential alternatives. PFRs can be broadly classified into three groups i.e. inorganic, organic and halogen containing PFRs [23]. Raman spectra of some of the commonly used PFRs are shown in Fig. 1. The three chlorine containing PFRs (TCEP, TCPP, TDCPP) all show prominent peaks in the 600–800 cm 1 region typically associated with C–Cl stretching [22]. As with BFRs, the individual PFR species are clearly distinguishable based on their unique spectral signatures. The acquired FR spectral library, shown in Fig. 1, highlights the utility of Raman
Polyurethane foam is one of the most extensively used polymer materials, with widespread applications in furniture and a variety of other consumer products. The widespread use of PUF makes it potentially a significant source of PUF related FR contamination in the environment. In recent years, Stapleton et al and Carignan et al. have investigated this particular class of FRs in terms of their presence in consumer products and the environment [14,20]. Here we present RMS based identification of FRs in PUF samples that have been previously characterized by Carignan et al. using gas chromatography negative chemical ionization mass spectrometry (GC/ECNIMS) and X-ray fluorescence spectroscopy (XRF) [20]. Given the detailed analytical information already available about these samples, they represent a unique opportunity for exploring the feasibility of RMS based identification of FRs in consumer products. Table 1 lists the PUF samples examined in this study along with the associated FRs and their respective concentrations as reported by Carignan et al. [20]. Carignan et al. identified TDCPP to be the primary FR in PUFs 7 and 8, with measured concentrations of 6.6% and 5.6%, respectively [20]. RMS analysis of PUFs 7 and 8 is shown in Fig. 2 along with the reference spectra for melamine and TDCPP. Melamine was identified as a major constituent in both PUF 7 and 8 based on spectral matching analyses. Melamine and its derivatives are classified as non-halogenated flame retardants and have been proposed as viable alternatives to Penta-BDE [23–25]. It is currently used in flexible polyurethane foam in concentration ranging from 30% to 40% melamine per weight of the polyol and is typically applied as a crystalline powder [25]. Strong melamine specific peaks (967.3 cm 1, 984 cm 1) evident in PUF 7 and 8 spectra suggest significant presence of melamine in the foams. This is consistent with the typical concentrations of melamine reported in the literature (30‐40%) [25], which is considerably higher than the TDCPP concentrations (o10%) reported by Carignan et al. [20]. In addition to melamine, PUF 7 spectrum also showed evidence of TDCPP along with peaks related to the polymer matrix (600–1800 cm 1) (Fig. 3). Polymer related peaks representing the PUF matrix were common to all the PUF samples examined in this study. The two individual PUF 7 spectra shown in Figs. 2 and 3 were acquired at two different locations on the sample and are spectrally distinct. The observed differences in spectral features correspond to differences in molecular composition at these two sites and as such are indicative of spatial heterogeneity in sample composition. The PUF 7 spectrum shown in Fig. 2 is characterized by strong melamine peaks suggestive of a melamine hotspot. The observed heterogeneous distribution of melamine in PUF 7 is Table 1 List of PUF samples analyzed in this study along with the FR species and the corresponding concentrations as reported by Carignan et al. [20].
Fig. 1. Reference Raman spectra of FRs commonly present in consumer products.
PUF
FRs (%)20
7 8 6 5 4 3
TDCPP (6.6) TDCPP (5.6) TBB (2.8), TPP (1.1), TBPH (1.3) Penta BDE (3.7), TPP (0.3) Penta BDE (5.3), TPP (0.4) Penta BDE (4.8), TPP (0.3), TDCPP (0.1)
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Fig. 2. RMS analyses of two different foam samples (PUF 7 and 8) showing spectral comparison with reference Raman spectra of melamine and tris(1,3-dichloro-2propyl) phosphate (TDCPP).
Fig. 3. Raman spectrum of the PUF 7 foam sample showing spectral matches with reference Raman spectra of tris(1,3-dichloro-2-propyl) phosphate (TDCPP), melamine, polyurethane foam (PUF). The red dotted lines identify position of the strongest TDCPP peaks.
consistent with the application of melamine as crystalline powder, which can create localized hotspots. A particular advantage of RMS analysis is that it enables simultaneous identification of multiple constituents in the sample by probing the entire Raman active compositional profile. For instance, in case of PUF 7, we were able to identify several components including melamine, TDCPP and the polymer matrix based on the acquired spectrum. In Raman analysis, spectral response is determined by concentration and Raman crosssection of the constituent molecular bonds. Therefore, the spectral response can be dominated by signals from constituents with higher concentration and/or Raman cross-section. An example of this can be seen in case of PUF 6, which was reported as containing multiple FR species—TPP, TBB and TBPH [20]. Fig. 4 shows acquired spectrum of PUF 6 along with reference spectra of the three constituent FR species. The PUF 6 spectrum is dominated by peaks arising from the polymer matrix, which is the primary constituent. In comparison, the FR related peaks are less prominent. TPP is identifiable based on two sharp peaks located at 1005 cm 1 (P–O–C anti-symmetric stretch in organ-ophosphorus compounds) and 3063 cm 1 (¼C–H stretch of the benzene ring) [22]. TBB and TBPH
Fig. 4. Raman spectrum of the PUF 6 foam sample showing spectral matches with reference Raman spectra of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), bis(2ethylhexyl)-tetrabromophthalate (TBPH), triphenyl phosphate (TPP). Dotted green, purple and red lines identify positions of the strongest peaks for TBB, TBPH and TPP, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
both show a sharp peak around 216 cm 1, indicative of the C-Br bond [22]. In addition to the 216 cm 1 band, TBB also has a sharp peak at 1555 cm 1 (benzene ring stretch), which distinguishes it from TBPH [22]. All of these FR related peaks are evident in the PUF 6 spectrum though they are less prominent compared to the PUF peaks. In addition to the above mentioned FR species, PUF 6 also showed some localized presence of melamine. The three remaining PUF samples (PUF 3, 4, and 5) were all reported as containing TPP and Penta-BDE in varying concentrations, Penta-BDE being the dominant FR species [20]. Fig. 5 shows acquired spectra of the three PUF samples. All three spectra have a sharp peak at 1005 cm 1 from TPP. They also contain singlet and doublet peaks in the 100–250 cm 1 region, which are characteristic of penta BDE [21]. Similar to PUF 6, these spectra also show strong response from the polymer matrix. In summary, RMS analysis of the PUF samples confirmed the presence of FR species previously identified by Carignan et al [20]. In addition, RMS analyses also identified the presence of melamine, not reported by Carignan et al [20]. These results also illustrate the simultaneous identification of multiple constituents in a sample, which is a particularly advantageous in terms of contaminant and source attribution in environmental monitoring. This is discussed further in the following section where we present RMS based characterization of select consumer products, simultaneously identifying both the polymer matrix and the associated FR species. 3.3. Identification of FR species and polymer matrices in consumer products Consumer products are a major source of FR related contamination, particularly in indoor environments [15,26–29] where migration of FRs from consumer items into the surroundings can take place via volatilization and/or physical weathering of products [15,30,31]. Several studies have highlighted the necessity of linking FR contaminants in the environment to their original sources [15,26]. In case of mechanical transfer of FRs via physical weathering of products, FR chemicals are often transferred in association with the product matrix. We have previously reported the identification of FRs together with the associated polymer matrix, in residential dust samples, which is suggestive of
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Fig. 5. RMS analyses of foam samples from three different sources with peak assignments for the identified FR species, penta BDE and triphenyl phosphate (TPP). Dotted red and green lines identify positions of the strongest peaks for penta BDE and TPP, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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mechanical transfer of FRs from consumer items into the environment via physical weathering [2,3]. Linking FR contamination to a specific consumer item necessitates knowledge of the product composition i.e. FR species and polymer matrix associated with the item. As mentioned earlier, Raman spectroscopy is well suited for this type of multicomponent analysis. To illustrate this point, we present RMS based characterization of three consumer items (car visor covering and, casing materials from a VCR and a computer monitor) with the goal of identifying the polymer matrices and the associated FR species. Fig. 6 shows acquired spectra of the three consumer materials along with reference spectra of the polymer and FR constituents identified through spectral library search. In all three cases, both the polymer matrix and the associated FR species are readily identifiable based on their unique spectral signatures. The car visor material consists of two FRs, deca-BDE and antimony trioxide, incorporated into a polyvinyl chloride (PVC) polymer matrix (Fig. 6a). The VCR casing material was identified as high-impact polystyrene (HIPS) with deca-BDE as the FR component (Fig. 6b). The polymer and FR components of the CRT casing were determined to be polycarbonate (PC) and TPP, respectively (Fig. 6c). Product specific spectral fingerprints offered by the RMS method
Fig. 6. RMS analyses of consumer products. (a) Raman spectrum of car visor material showing spectral match with reference Raman spectra deca-BDE, antimony trioxide (Sb2O3) and polyvinyl chloride (PVC). (b) Raman spectrum of the VCR casing showing spectral match with reference Raman spectra of high impact polystyrene (HIPS) and deca-BDE. (c) Raman spectrum of the CRT casing showing spectral match with reference Raman spectra of poly carbonate (PC) and triphenyl phosphate (TPP). Insets: 50 reflected light image showing the region of RMS analysis.
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described here can be used for FR identification and source attribution in a variety of environmental samples and consumer products. 4. Conclusion The results presented here highlight the utility of Raman spectroscopy as a non-invasive analytical tool for the identification and source attribution of FRs in consumer products and environmental samples. RS based identification relies on the availability of relevant spectral libraries of reference chemicals in order to accomplish chemical identification through spectral matching. We have compiled a reference spectral library of several commonly used FR chemicals to facilitate the identification process. The acquired spectral library has been used successfully to identify FR additives in a selection of commercially used polyurethane foam samples. The foam samples had been previously characterized by GC–MS as part of a separate study [20]. Our results are in excellent agreement with the previous study and also offer additional information such as the presence of melamine, another FR species. We have also identified polymer matrices and FR species associated with three commonly used consumer items to illustrate the applicability of RS for source characterization. Acknowledgements S.G. and H.F. would like to thank Dr. Thomas Webster (Boston University) and Dr. Heather Stapleton (Duke University) for access to the PUF samples. S.G. would also like to thank Dr. Jeff Wagner (CDPH) for access to consumer product samples and Dr. Simon Ip for helpful discussions. References [1] S.D. Shaw, et al., Rev. Environ. Health 25 (4) (2010) 261–305. [2] S. Ghosal, J. Wagner, Analyst (2013) 3836–3844138 (2013) 3836–3844.
[3] Wagner, J., et al., Morphology, Spatial Distribution, and Concentration of Flame Retardants in Consumer Products and Environmental Dusts using Scanning Electron Microscopy and Raman Micro-spectroscopy. 2012. [4] S. Kikuchi, et al., Anal. Sci. 20 (2004) 1111–1112. [5] California Bureau of Electronic and Appliance Repair, H.F.a.T.I., Requirements, Test Procedure and Apparatus for Testing the Flame Retardance of Resilient Filling Materials Used in Upholstered Furniture., in Technical Bulletin 117 S.o.C. D.o.C. Affairs, (Ed.), 1975: Sacramento, CA. [6] Information, G., Flame Retardants (US Market & Forecast), in Advanced Material Market Research Report. 2012, Global Information p. 245. [7] J.K. Stross, et al., Toxicol. Appl. Pharmacol. 58 (1981) 145–150. [8] J. Jacobson, et al., Am. J. Public Health 74 (4) (1984) 378–379. [9] T.A. McDonald, Chemosphere 46 (5) (2002) 745–755. [10] California Bureau of Electronic and Appliance Repair, H.F.a.T.I., Requirements, Test Procedure and Apparatus for Testing the Flame Retardance of Resilient Filling Materials Used in Upholstered Furniture., S.o.C.D.o.C. Affairs, (Ed.), 2013: Sacramento, CA. [11] I. van der Veen, J. de Boer, Chemosphere (2012) (Journal Article). [12] A. Kierkegaard, J. Bjorklund, U. Friden, Environ. Sci. Technol. 38 (12) (2004) 3247–3253. [13] M.J. Guardia, R.C. Hale, E. Harvey, Environ. Sci. Technol. 40 (2006) 6247–6254. [14] H.M. Stapleton, et al., Environ. Sci. Technol. 45 (2011) 5323–5331. [15] T.F. Webster, et al., Environ. Sci. Technol. 43 (9) (2009) 3067–3072. [16] E. Eljarrat, D. Barceló, TrAC Trends Anal. Chem. 23 (10) (2004) 727–736. [17] M.J. Pelletier, Analytical Applications of Raman Spectroscopy, Blackwell Science Ltd., Oxford, 1999. [18] G.J. Puppels, et al., J. Raman Spectrosc. 22 (1991) 217–225. [19] S. Ghosal, J.M. Macher, K. Ahmed, Environ. Sci. Technol. 46 (11) (2012) 6088–6095. [20] C.C. Carignan, et al., Environ. Sci. Technol. 47 (23) (2013) 13848–13856. [21] G.C. Stevens, et al., A new rapid analysis method for fire retardants in polymers, in: InterFlam, Interscience Communications: University of Nottingham, Nottingham, UK, 2010. [22] J.B. Lambert, H.F. Shurvell, R.G. Cooks, Introduction to Organic Spectroscopy, Macmillan, New York, 1987. [23] I. van der Veen, J. de Boer, Chemosphere 88 (2012) 1119–1153. [24] S.L. Waaijers, et al., Rev. Environ. Contam. Toxicol. 222 (2013) 1–71. [25] U.S.E.P. Agency, Environmental Profiles of Chemical Flame-Retardant Alternatives for Low-Density Polyurethane Foam, U.S.E.P. Agency, 2005. [26] J.G. Allen, et al., Environ. Sci. Technol. 42 (11) (2008) 4222–4228. [27] Suzuki, G., et al., PBDEs and PBDD/Fs in House and Office Dust from Japan., in Organohalogen Compounds. 2006: Oslo, Norway. p. 1843–1846. [28] H.M. Stapleton, et al., Environ. Sci. Technol. 39 (4) (2005) 925–931. [29] S. Hazrati, S. Harrad, Environ. Sci. Technol. 40 (24) (2006) 7584. [30] Kose, T., et al., Determination of the Emission Amount of Organic Pollutants from Household Products Using a Model Room., in Organohalogen Compounds. 2008: Birmingham, England. p. 2305–2308. [31] G. Suzuki, et al., Environ. Sci. Technol. 43 (5) (2009) 1437–1442.
