Helping contaminants emerge: The application of high-resolution mass spectrometry to non-targeted analysis of organic pollutants

Keynote Speaker
Oral Presentation

Prepared by P. Ferguson, G. Getzinger
Duke University, Pratt School of Engg & Nicholas School of the Environment 121 Hudson Hall, Box 90287, Durham, North Carolina, 27708-0287, United States


Contact Information: lee.ferguson@duke.edu; 919-660-5454


ABSTRACT

The rate of identification of new and emerging contaminants in the aquatic environment has been limited heretofore by reliance on targeted analytical techniques, which depend on compound-by-compound verification using authentic standards. Recent advancements in high-resolution mass spectrometry (HRMS) and its application to the field of environmental chemistry has for the first time made possible identification of emerging contaminants in complex environmental mixtures without a priori knowledge of contaminant identity or occurrence. In this study, we present a strategy and analytical workflow based on Orbitrap HRMS and MS/MS in conjunction with new informatics tools (e.g. data processing, spectral library searching, and literature mining) for identification of emerging environmental contaminants in environmental samples without the aid of user-defined molecular databases. In this approach, high resolution (R>100,000) accurate mass (mass error < 2 ppm) analyses of water & wastewater extracts are subjected to recursive peak assignment, adduct grouping, isotope pattern scoring, and molecular formula assignment. Chromatographic features and molecular formulas are then filtered using empirical indices (e.g., chromatographic peak shape, mass accuracy, isotopic pattern fit) and heuristic rules for the assignment of probable molecular formulas. Filtered chromatographic features are subjected to confirmation criteria for tentative identification. To this end, we demonstrate the capabilities of rule-based in silico fragmentation to aid in the structural elucidation of unknown contaminants without the benefit of reference standards. Utilizing a suite of environmentally relevant compounds, we have established a scoring scheme for assigning the certainty of identification and analytical figures of merit. Importantly, we demonstrate that the developed methodology exhibits low false-positive rates and acceptable false-negative rates for the intended applications.
I will discuss our application of these methods to identify emerging contaminants in several important environmental systems, including:
Examination of polar organic micropollutant removal and formation of transformation products during wastewater treatment
Identification of chemical additives and other organic contaminants relevant to consumer products in house dust as a proxy for human exposure to these chemicals
Evaluation of degradation products formed in the biotransformation of the complex nonionic surfactants used in dispersants applied to the Deepwater Horizon oil spill