Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame-retardant (BFR) additives, common in plastics (for example, electronic casings, computers, and televisions), circuit boards, polyurethane foam (furniture padding), and textiles. These widely used chemicals have been manufactured since the mid-1970s. However, following evidence that constituents of these mixtures bioaccumulate and disrupt biological processes such as the endocrine system, the manufacture of two of the three common formulations (penta- and octa-BDEs) was discontinued in the U.S. in 2004. This followed their ban by the European Union earlier that year (2). These two formulations, as well as the still-manufactured deca- (consisting of >97% by weight of BDE-209), are considered environmentally persistent and globally dispersed (3,4). Sources include industries producing or using PBDEs, as well as releases from finished products (5,6). The latter suggests that PBDEs will continue to be released into the environment long after the 2004 cessation in production. Even before termination of penta and octa production, deca- was the most widely used PBDE formulation [>83% 2001 global production (7)]. It is considered a lesser health concern because of its lower bioaccumulation potential, attributed to its extreme hydrophobicity and significant molecular mass (959 Da). However, reports have indicated that BDE-209 is bioavailable (8–10), although to a lower extent than the constituent congeners of the penta- and octa-formulations. Continued use of deca-BDE might be problematic because it has been reported to undergo abiotic [photolytic (11) and metal oxide reduction (12)] and biotic debromination (9,10), thus potentially adding to existing burdens of the lower brominated diphenyl ethers.

Like polychlorinated biphenyls (PCBs), 209 different PBDE congeners are feasible, and the same IUPAC scheme is used for their naming. In reality, the three commercial mixtures tend to be much simpler than those of PCBs, consisting primarily of 39 individual PBDE congeners (7). This is due to the directing influence of the oxygen and the large size of the bromine atoms (Figure 1). PBDEs are analyzed routinely by gas chromatography (GC) coupled with electron-capture detection (ECD), or more commonly, low resolution mass spectrometry (LRMS), operated either in electron ionization (EI) or electron- capture negative ionization (ECNI) modes. High resolution MS (HRMS) also has been used and has a number of advantages over LRMS (such as increased sensitivity and selectivity), but it requires more experienced users and is much more costly and labor intensive (13). Selective ion monitoring (SIM) ECNI (e.g., monitoring bromine ions ([⁷⁹Br]^– and [⁸¹Br]^–) has been shown to be a very sensitive technique and is used widely for the determination of low sub-parts-per-billion (ppb) levels. However, like ECD, this technique can result in misidentification (for example, 2,294,49,5,69-hexabromodiphenyl ether (BDE-154) is coeluted with 2,294,49,5,59-hexabromobiphenyl (BB-153) (14). Further spectral information can be obtained by scanning multiple ions, or an extended range of ions, at the loss of some sensitivity.

Ion fragment clusters centered on the molecular ion [M]⁺ and the loss of two bromines [M-2Br] have been observed previously in PBDE EI spectra (13). This approach, in combination with retention-time data, has found utility for compound identification. However, acquisition of standards for all 209 PBDEs can cost from $20,000 to $30,000, and most searchable mass spectra libraries presently do not contain PBDEs (for example, NIST/EPA/NIH Mass Spectral Library with Search Program: NIST 05, Ver. 2.0d). So most laboratories focus on a subset of congeners previously identified in the three commercial mixtures. "Unknowns" typically are only characterized to the level of homologue (for example, hepta-BDE). Consequently, this lack of specificity limits specific congener identification, toxicological studies, and degradation pathways for these quasi-labeled PBDEs.