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Post-Target Analysis of Halogenated Flame Retardants Using Mass Defect Plots

Post-Target Analysis of Halogenated Flame Retardants Using Mass Defect Plots content piece image
Targeted analytical methods are often very robust, sensitive, and selective; yet, a conundrum for many researchers doing complex environmental analysis is "What else is in my sample“? Time-of-flight mass spectrometry (TOFMS) is unsurpassed for non-target analysis because full range mass spectra are acquired simultaneously with minimal mass bias at acquisition rates suitable for narrow gas chromatographic peaks. This provides a number of advantages including the possibility of deconvolving chromatographic interferences using modern software, further enhancing the ability to isolate and identify a greater number of compounds.
Analysts are continuously building a tool box for compound discovery which may include multivariate statistical analysis, high resolution mass spectrometry, and soft or selective ionization techniques. Mass defect plots are another tool to add to the analyst’s arsenal. Mass defect is the difference between the nominal and exact masses of a compound or its fragments.1 Halogenated compounds have characteristic mass defects that make them readily distinguishable from most other compound classes. Two fairly recent papers have highlighted the utility of Cl-H mass defect for the identification of halogenated environmental contaminants.2,3 Mass defect (Cl-H) can be calculated according to the following equations, where the IUPAC mass is the observed mass, and the scaling factor for chlorine substituted for hydrogen equals 34/33.960479:
Cl-H Scaled Mass = IUPAC Mass × Scaling Factor
Cl-H Mass Defect = Cl-H Scaled Mass – Nominal Cl-H Scaled Mass

In this study we used non-target analysis in the form of Cl-H mass defect plots, to identify halogenated contaminants in eels (Anguillia rostrata) from Lake Ontario, Canada. This study was meant to serve as a proof-of-concept for the identification of unknown compounds in complex matrices.