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Development of the First Certified Reference Materials for Several Brominated Flame Retardants in Polymers Thomas P. J. Linsinger,* Almuth Birgersson-Liebich, Andre´e Lamberty, Francesca Pellizzato, Tony Venelinov, and Stefan Voorspoels European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, 2440 Geel, Belgium The first reference materials certified for several polybrominated flame retardants in polymers were developed. Commercially available polyethylene and polypropylene were fortified with technical mixtures of Pentabrominated diphenylether (Penta-BDE), Octa-BDE, Deca-BDE, and Decabrominated biphenyl (BB) (where the capitalized forms refer to the technical mixtures). Homogeneity was tested on 20 units of each material, and between-unit variation was confirmed to be below 4% for all congeners. Stability was assessed after storage of samples for 1 year at 4, 18, and 60 °C. Uncertainty of degradation during transport was found negligible for all congeners, whereas uncertainty of degradation for storage of 24 months at 4 °C was estimated between 2% and 11%. A characterization intercomparison involving 16 laboratories was organized. After exclusion of technically doubtful results, betweenlaboratory standard deviations ranged from 3% to 12%, making this intercomparison the best for this field of analysis so far. Statistical analysis revealed that the use of isotopically labeled internal standards did not improve analytical precision in this study. The good comparability, together with the independent confirmation of the assigned mass fractions via the total bromine content as well as by using non-GC/MS-based methods, allowed for the first time the certification of polymer materials for several brominated flame retardants. Brominated diphenylethers (BDEs) belong to a class of brominated compounds which are, apart from the presence of the oxygen atom between the phenyl rings, structurally similar to polychlorinated biphenyls (PCBs) and, therefore, share the same numbering of congeners as proposed by Ballschmiter et al.1 Brominated biphenyls (BBs) are the bromine homologues of PCBs; hence, the same numbering system is used. They are commercially available as technical mixtures of various congeners of which the name is derived from the average degree of bromination. For example, technical Penta-BDE consists of various tetra-, penta-, and hexabrominated congeners. To avoid confusion we will in this manuscript follow the convention that names in * To whom correspondence should be addressed. E-mail: thomas.linsinger@ ec.europa.eu. (1) Ballschmiter, K.; Bacher, R.; Mennel, A.; Fischer, R.; Riehle, U.; Swerev, M. J. High Resolut. Chromatogr. 1992, 15, 260–270.
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capital letters refer to the technical mixtures, whereas lowercase letters refer to the congeners themselves. Therefore, “Octa-BDE” refers to the technical mixture with an average degree of bromination of 8, whereas “octa-BDEs” refers to all octabrominated congeners. Technical Deca-BDE and Deca-BB are relatively pure substances, consisting of more than 97% pure BDE-209 and BB-209, respectively. Congener patterns of the technical mixtures depend on the reaction conditions and vary between producers and even batches. The European Commission Directive on the “Restriction of the use of certain hazardous substances in electrical and electronic equipment” (RoHS)2 bans the use of certain brominated flame retardants (BFRs) in electric and electronic devices since July 1, 2006 unless no technical substitutes exist, and limit values of 1 g/kg (0.1%) for the sum of polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) have been set.3 Similar legislation has been adopted by, e.g., Australia, Canada, Korea, and Taiwan, the People’s Republic of China, Japan, and several states in the United States (e.g., Washington, California, Maine). Enforcement of this legislation requires, among other measures, testing of materials and products for their content of BFRs. Reliable quality of the determination of BFRs is therefore crucial. Although chemical analysis of BFRs seems quite straightforward (extraction, cleanup, quantification by gas chromatography/ mass spectrometry (GC/MS)), experience has shown that the opposite is true.4,5 Several aspects that are inherently coupled to this group of chemicals can hamper sound analysis. Most problems are situated in the final quantification step. Several injection techniques for the introduction into the GC system, all with their specific drawbacks, are available. Split/ splitless injectors are robust, and perform well if injected extracts are dirty, but temperature-induced degradation of analytes may occur if the injector temperature is too high. This technique is also known to discriminate analytes with high molecular weight. Lowering the injector temperature will discriminate even more (2) Directive 2002/95/EC of the European Parliament and of the Council of 27 January 2003 on the restriction of the use of certain hazardous substances in electrical and electronic equipment, OJ L 37, 13.2.2003, 19-23. (3) Decision 2005/618/EC of the European Commission of 18 August 2005 amending Directive 2002/95/EC of the European Parliament and of the Council for the purpose of establishing the maximum concentration values for certain hazardous substances in electrical and electronic equipment, OJ L 214, 19.8.2005, 65-65. (4) De Boer, J.; Cofino, W. P. Chemosphere 2002, 46, 625–633. (5) De Boer, J.; Wells, D. E. Trends Anal. Chem. 2006, 25, 364–372. 10.1021/ac900139r CCC: $40.75 2009 American Chemical Society Published on Web 03/26/2009
against high molecular weight analytes. This can be overcome by application of a pressure pulse.6 The issue of discrimination of high molecular weight analytes is of special importance when analyzing BFRs with high bromine content, such as nona-BDEs and BDE-209. An alternative is offered by the programmed temperature vaporization (PTV) injector, whose injection parameters can be modified to optimize the transfer of BFRs from the liner to the column. PBDEs with a low to medium degree of bromination (tri- to hepta-BDEs) usually are analyzed on capillary columns of 30-50 m length to achieve sufficient resolution for all congeners of interest. Column diameter is preferably 5000 amu
latter for a period of 2 years for storage at 4 °C. For the uncertainty contribution for 2 years of storage, all studies were combined to have more data points per time point. As degradation proceeds faster at higher temperatures, combining results from 4 °C with those from 18 and 60 °C still results in a conservative estimate of stability. In this way, the 1 year study could be extrapolated to estimate potential degradation over 2 years without falsely inflating the uncertainties. Characterization. Setup of the Study. Characterization aimed at randomization of significant laboratory bias. Therefore, an intercomparison of laboratories that participated successfully in previous intercomparisons on the determination of BFRs in polymers was organized. Fulfilment of quality management requirements ensured that the technical standard had been maintained from the time of demonstration of competence to the actual measurement. Most participating laboratories were accredited to ISO 17025, even if the measurements are in many cases not covered by the scope of accreditation. Most laboratories were specialized in analysis of industrial and polymer samples, although also two environmental analysis laboratories participated in the study. The environmental laboratories had demonstrated their competence in the analysis of polymer samples by submitting results on a quality control material consisting of BFRs in poly(ethylene terephthalate). Laboratories were free to choose their own methods, i.e., methods they were familiar with. The predominance of industrial analytical laboratories led to deviations of the usual practice in environmental analysis laboratories with regards to the choice of columns and injectors. Sixteen laboratories were selected to cover different extraction and quantification methods. A short summary of the methods is given in Table 2; a detailed description is given in the Supporting Analytical Chemistry, Vol. 81, No. 10, May 15, 2009
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Information. Before the start of the measurements, a telephone conference was organized in which the detailed measurement protocol was discussed and during which potential misunderstandings were solved. As can be seen in Table 2, a wide variety of extraction techniques, internal standards, and GC/MS systems were employed. Extraction: Most laboratories used toluene as extraction solvent, with Soxhlet extraction being the dominant technique. Extraction times ranged from 1 to 24 h. Other techniques included ultrasonic-assisted extraction, pressurized liquid extraction, and static extraction. One laboratory dissolved the samples completely. Internal standards: A variety of internal standards was used. Several laboratories used either one or several PCBs as internal standard for all analytes, whereas others employed a suite of PCBs, fluorinated diphenylethers, isotopically labeled as well as nonlabeled PBDEs. GC systems: GC systems varied widely with respect to injection systems and columns used. Most laboratories determined all samples on one column, but two laboratories employed two columns. In one case, only nona- and decabrominated BDEs as well as BB-209 were analyzed on the second column, whereas the second laboratory also analyzed octabrominated congeners on the second column. Determination of all congeners on a single column is usually not recommended as a long GC run leads to degradation of BDE-209. However, the samples contained few of the lower brominated congeners due to their industrial origin, thus making long GC runs superfluous. Temperature programs for laboratories using only one column ranged from 15 to 28 min, which is short enough to avoid degradation.Yet another laboratory used two columns to avoid some coelutions, delivering two complete data sets. Quantification: All laboratories used mass spectrometry as quantification technique, but also here the MS systems (quadrupole, two sectorfield) and ionization techniques varied.In addition, two laboratories performed measurements by highperformance liquid chromatography with UV detection (HPLCUV) and ion-attachment mass spectrometry (IA-MS), respectively, to confirm the results from GC/MS measurements.Each laboratory received two bottles of each of the two materials and two ampules of a quality control solution. These two quality control solutions were candidate CRMs provided by the U.S. National Institute for Standards and Technology (NIST), which had not been released yet, but whose certificates were in the final review stage. The materials consisted of BDE-209 in isooctane (candidate SRM 2258) and a PBDE mix in isooctane (candidate SRM 2257). The use of these solutions was preferred over the possibility to use one of the Japanese CRMs, as those are only certified for BDE-209. Each laboratory was requested to perform six independent measurement series. Each measurement series consisted of a complete calibration line, determination of a method blank, measurement of a quality control sample, and measurement of one extract of the two materials.Two quantitative assessments for the technical quality were available. Laboratories’ results for the quality control solution were compared to the candidate certified values. Results deviating significantly from the candidate certified 3796
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values were excluded from the evaluation. In addition, the Br content calculated on the results for the various congeners was compared to the Br content, which had been determined independently by several laboratories using neutron activation analysis as well as destructive methods. Data sets were excluded if the calculated Br content was significantly above the candidate certified Br content. A technical discussion was held with the laboratories after receipt of the results. This discussion aimed at identification of analytical problems that would result in exclusion of data sets on technical grounds. Statistical Evaluation. Results accepted on technical grounds were subjected to a further statistical evaluation. It was checked whether the data followed normal distributions and whether variances for each congener were homogeneous. ANOVAs were performed to evaluate average within- and betweenlaboratory standard deviations. These evaluations were performed with a modified version of the software SoftCRM.25 No outliers were eliminated solely on statistical grounds. In addition, within-laboratory standard deviations were investigated more deeply using the set of results accepted on technical grounds: regression analyses of absolute/relative within-laboratory standard deviation versus mass fraction were performed. With the use of ANOVA, it was investigated whether the within-laboratory standard deviation differed between congeners. A regression analysis of recovery of the assigned value versus the particle size used was performed to investigate a potential influence of the particle size on the results. Finally, repeatability of results obtained using isotopically labeled standards was compared to the one obtained using nonisotopically labeled standards. Results obtained using a different isotopically labeled congener than the one quantified were classified as obtained by “nonlabeled” standards. For these investigations, results from both materials were pooled into one data set. Statistical evaluation was performed using Statistica 7.0. RESULTS AND DISCUSSION Homogeneity. The results of the homogeneity evaluations are shown in Table 3. As can be seen in Table 3, between-bottle variation was confirmed to be below 4% for all congeners, proving the suitability of the materials as CRMs. Stability. Of the 84 regression lines (14 congeners × 3 temperatures × 2 materials), only the slope of BDE-127 in the polyethylene material was found significant after 1 year of storage at 60 °C. This finding is actually below the expected value of 4 statistically significant slopes at a confidence level of 95%. In addition, the mass fraction of BDE-127 apparently increases, which could only be explained by degradation of another congener, forming BDE-127, which is extremely unlikely and is most likely an analytical artifact. In any case, BDE-127 is not certified, so the slope, even if real, is irrelevant. The uncertainties of stability during dispatch and storage are listed in Table 4. As can be seen in Table 4, potential degradation during transport is
