Application of pattern deconvolution strategies for the estimation of bromochloro alkane concentrations in indoor dust samples

Bromochloro alkanes (BCAs) are a class of flame retardants similar in structure to polychlorinated alkanes (PCAs), which are the major component of short-chain chlorinated paraffins (SCCPs) listed as Persistent Organic Pollutants under the Stockholm Convention. BCAs have recently been detected for the first time in environmental samples. Due to the complete lack of commercially available analytical standards, no method for quantifying BCAs has been reported to date. In this study, 16 custom-synthesised standards with mixed bromine and chlorine halogenation and carbon chain lengths ranging from C₁₀ to C₁₇ were characterized by liquid chromatography and Orbitrap high-resolution mass spectrometry and used to assess the applicability of pattern deconvolution quantification strategies for BCAs in indoor dust. Br_1-9 and Cl_1-8 BCAs were detected as [M + Cl]^- adduct ions among the C₁₀ to C₁₇ standards, as well as numerous PCA homologues. After applying correction factors to account for the presence of PCAs in the standards, triplicate fortification experiments using varied halogenation composition and concentration determined an average measurement accuracy of 81% over the carbon chain lengths studied and coefficient of variance ≤20% between replicates. Overall, approximately 89% of the ΣBCA concentrations quantified in the fortification trials met the European Union Reference Laboratory's accuracy acceptability criteria recommended for PCAs, between 50 and 150%. Application of the BCA pattern deconvolution quantification procedure to seven representative indoor dust samples from the United States of America revealed a low correlation between the homologue distribution in the samples and the prototype standards (R² ≤ 0.40), which precluded reliable quantification. This study indicates that pattern deconvolution is an appropriate strategy for quantifying BCAs in environmental samples, but that a large set of appropriate mixture standards will be required before more reliable estimates of BCA concentrations can be achieved in indoor dust.