Correspondence/Rebuttal pubs.acs.org/est
Comment on “Mutagenic Azo Dyes, Rather Than Flame Retardants, Are the Predominant Brominated Compounds in House Dust”
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compound at retention time 11.7 min (533.0724) was reported in error, as the calculated m/z of the proposed formula, C23H23O7N3Br, should be 532.0725. The reported m/z of 533.0724 also conflicts with the m/z of the residual precursor ion in Figure 3d of Peng et al. (532.0708), as well as that of the corresponding ID# 107 (m/z = 532.0719 at retention time = 11.7 min) in the Supporting Information. Presuming that the m/z value reported in the Supporting Information is correct for this compound, the neutral mass is 532.0714 after subtracting the electron mass. Assuming a mass accuracy of ±2.5 ppm, 133 unique molecular formula candidates are possible from the elements C0−45H0−79N0−16O0−19P0−5F0−22Br1−1 (derived from elemental ranges of compounds with similar mass in PubChem and assuming no Cl or S). These candidates were narrowed to 68 likely formulas based on valence and element ratio compliance with the “Seven Golden Rules for heuristic filtering of molecular formulas”.4 The authors’ proposed formula (C23H23O7N3Br) fails the LEWIS rule of valence (e.g., that all atoms have completely filled s, p-valence shells) and thus does not appear on this list of 68 formulas. Even with ∼200 Da. We have applied next-generation computational mass spectrometry tools to identify several of the compounds listed in Table 1 of Peng et al. With our data for the example described above (and shown in Figure 1), we used Sirius 3.35 (https://bio.informatik.uni-jena.de/software/sirius/) to assess 3960 candidate formulas from an expanded chemical alphabet of C0−45H0−79N0−16O0−19P0−5S0−9Br0−1F0−22Si0−9 (“worse case scenario”). The top-ranked formula was C21H21BrN6O6 (mass measurement accuracy for [M + H]+ = 0.33 ppm, consistent with the
