Analysis of Brominated Flame Retardants Using the AutoSpec Ultima NT

In this application note, brominated flame retardant compounds such as the PBDEs are analyzed using AutoSpec Ultima NT.

Brominated flame retardants (BFRs) are the largest group of organic flame retardants currently in use. A key constituent of these materials are PBDEs, polybrominated diphenyl ethers, which are added to plastics to decrease the likelihood and intensity of fire in a wide variety of products, including vehicles, furniture, textiles, carpets, building materials, and electronic circuit boards. PBDEs are additive flame retardant compounds, being mixed (rather than chemically bonded) with polymers as plastics are being made and because they do not bind chemically with the plastic, they leach continuously out of the final product. 

PBDEs are both lipophilic (they concentrate in lipids, or fats) and extremely resistant to physical, chemical, or biological degradation making them highly persistent in the environment and bio-accumulative. Environmental contamination occurs due to passive transport of PBDEs via water and air currents, but in addition PBDEs are also actively transported and dispersed because they are a prominent contaminant in sewage sludge, which is sprayed onto farmers' fields. 

The toxic effects of PBDEs have not been fully determined, however several studies indicate that commercially obtained penta- and tetra-BDE are endocrine disrupters, which can exert effects on the thyroid system. The effects of penta-BDE on thyroxine and the thyroid gland are considered to be principally due to the induction of liver enzymes, although several mechanisms may operate. Tetra- and penta-BDEs are used in polyurethane and have been found to have high bioconcentration rates, while bioaccumulation of the octa- and deca-BDEs often used in electronics is currently thought to be less significant. The penta brominated diphenyl ether (penta-BDE) formulation will be banned in the European Union (EU) in 2003. 

PBDEs now contaminate human milk and have also been found in human fatty tissue and in human blood serum. These compounds have also been found in multiple species of wildlife and in particular marine life, including sperm whales, indicating that the compounds have reached deep ocean waters.

The most common BDE congeners found in biological samples are BDE-47 (2,2',4,4'-tetra BDE) and BDE-99 (2,2',4,4',5-penta-BDE), the structures are shown in Figure 1.

Analysis of PBDEs and other brominated flame retardant constituents in complex environmental matrices requires a selective, sensitive, and quantitative method of detection. High resolution GC-MS is the analytical method of choice for detection and quantification of PBDEs, elevated resolution being necessary to confirm the identity of individual ion clusters.¹ EI (electron impact) is the preferred ionization method, giving characteristic mass spectra containing M⁺, M-Br⁺ and M-Br²⁺ ions. Negative ion chemical ionization (CI^-) is a less favorable approach, as Br^- and HBr dominate PBDE spectra, thus reducing selectivity. 

The sample used was a mixture of six PBDE congeners; tetra-brominated BDE 47, 66, and 77 and penta-brominated 85, 99, and 100. 

To determine the quantitative linearity and estimate the limits of detection, standards were prepared from 25 fg/μL to 500 pg/μL and injected in triplicate. 

Qualitative data was obtained using a 500 fg/μL mixed standard. 

The exact mass measurement capability of the Waters Micromass AutoSpec Ultima NT was then used to confirm the identity of a higher molecular weight deca-brominated BDE using voltage scanning.

The full scan spectrum of penta-brominated BDE 99 is shown in Figure 1. The spectra of the BDEs all show isotope patterns characteristic of brominated compounds. Figure 2 shows an expanded view of the molecular ion region of the spectrum of BDE 99 (bottom) and the theoretical isotope pattern generated by MassLynx isotope modelling (top). A characteristic of magnetic sector instruments is the mass spectral quality and it can be seen that the isotope ratios in the acquired spectrum are almost identical to the theoretical; Figure 3 shows the same for the tetra-brominated BDE 47.

Figure 4 and 5 show the full scan mass spectra of BDE 77 (non-ortho) and BDE 47 (ortho). The spectrum of BDE 47 shows less loss of Br₂ from the molecular ion than BDE 77 due to the spatial separation of the Br atoms in the molecule.

Figures 6 and 7 show calibration curves for BDE 47 and BDE 99 from 25 fg to 500 pg. Excellent sensitivity and linearity was observed for all congeners and all data points met the isotope ratio criteria of ±15% of theoretical on the 2 major ions for each brominated group.

Figure 8 is the molecular ion region of the exact mass spectrum obtained using voltage scanning of decabrominated BDE with the calculated elemental composition of the isotopes. The deca-brominated BDE shows a loss of Br₂, which corresponds to the elemental composition results. The exact mass measurement capability of the AutoSpec Ultima NT is illustrated by the mass accuracy results, which were calculated to be 2.1 ppm RMS.

Analysis of Brominated Flame Retardant compounds such as the PBDEs requires gas chromatography coupled with the selectivity, sensitivity and dynamic range of high resolution mass spectrometry. The AutoSpec Ultima NT provides unmatched performance for this analysis.

1.  Alaee, M. et al, Determination of Brominated Diphenyl Ethers in Environmental Matrices, Proc. 46th ASMS Conf. Mass Spectrom. Allied Topics, Orlando, FL, May 31-June 4, 1998, page 739.