Recent developments in ion source, analyzer and detector design of gas chromatography (GC) quadrupole time-of-flight mass spectrometry (MS) (GC/Q-TOF) systems has resulted in improved sensitivity and resolution. Such instruments may now be feasible alternatives to GC high-resolution magnetic sector MS (GC-HRMS), offering high sensitivity and high selectivity. The performance of such a system was evaluated in the current study for the analysis of environmental samples. The sensitivity was good with the lowest point of the calibration graph around 10 fg for tetra- and penta-congeners. Target analysis of in-house reference materials (RMs) show good agreement between GC/Q-TOF, GC-HRMS data and the average RM values. The GC/Q-TOF data for the toxicologically most relevant congeners (PCB126, 2,3,7,8-TCDD, 2,3,7,8TCDF, 1,2,3,7,8-PeCDD, 1,2,3,7,8- and 2,3,4,7,8-PeCDF) were within 25 % of the GC-HRMS and RM values. Similarly, the dioxin toxic equivalency values (TEQs) were within 19 % of the comparison data. The utility of the GC/Q-TOF systems extends beyond trace-analysis of e.g. dioxins. The entire full-spectrum data is written to disc and is available for various postacquisition tasks, such as suspect and non-target screening. To illustrate this we have screened a sediment sample for dioxin-analogues such as polychlorinated naphthalenes (PCNs), dibenzothiophenes (PCDTs) and thianthrenes (PCTAs) and polybrominated dioxins and dibenzofurans (PBDD/Fs). We also used non-target screening workflows to find additional planar halogenated compounds. Suspect screening revealed PCNs, PCDTs, and PBDDs in sediment samples, with PCNs as the most abundant compound class. Non-target screening showed that PAHs dominated the dioxin fraction and also revealed many halogenated PAHs. No PCTAs were found, but an interfering signal was noted during octa-CTA screening. Its spectrum displayed a tetrabromo isotope cluster at (monoisotope) m/z 492.730, and another tetrabromo cluster at [M-15]+, likely corresponding to a methyl loss. Molecular formula generation returned C13H7NBr4 as the most likely formula, but a SciFinder search did not return any candidate. Another search for the in-silico demethylated analogue did returned a likely candidate, the halogenated natural product 1,3,6,8-tetrabromocarbazole (TB-CZ), which has been reported in Great Lakes sediment. It was postulated that the unknown was 1,3,6,8-tetrabromo-9-methyl-carbazole; formed by bio- methylation of TB-CZ.

Target, suspect and non-target screening of dioxin-like compounds in environmental samples using a sensitive high-resolution time-of-flight mass spectrometer

255th National Meeting (2018)

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