Utilization of Negative Chemical Ionization to Expand Nontargeted Screening of Halogenated Organics in Great Lakes Top Predator Fish

Nontargeted screening (NTS) of halogenated contaminants in biota is part of the routine monitoring of the Great Lakes ecosystem. NTS can give insight into new chemicals with possible persistent, bioaccumulative, and toxic (PBT) properties and help quantify known PBT's degradation and transformation products. The most common ionization technique for NTS is electron impact ionization (EI) due to the consistent and easily standardized fragmentation patterns. This research uses electron capture negative ionization (ECNI) as a complementary technique to broaden the range of halogenated contaminants detected in the Great Lakes. ECNI has higher sensitivity and selectivity to halogenated compounds compared to EI. GC × GC-HR-ToF MS with a multimode ion source (MMS) offers consecutive runs in EI and ECNI modes using the same chromatographic setup, facilitating retention time alignment. The exact mass measurements help in identifying compounds found only in ECNI. A total of 85 novel halogenated features were detected, 78% of which were detected only in ECNI. Only 9% of the features were detected in both modes, indicating that ECNI is a necessary complementary technique for NTS of halogenated features.