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Improving High Throughput Exposomics through EPA’s Non-Targeted Analysis Collaborative Trial (ENTACT)
Citation:
Singh, R., A. Chao, X. Rui Xia, D. Shea, J. Sobus, AND E. Ulrich. Improving High Throughput Exposomics through EPA’s Non-Targeted Analysis Collaborative Trial (ENTACT). American Society for Mass Spectrometry Conference, San Diego, CA, June 03 - 07, 2018.
Impact/Purpose:
We are conducting EPA’s Non-Targeted Analysis Collaborative Research Trial (ENTACT) to evaluate the state-of-the-science for suspect screening (SSA) and non-targeted analysis (NTA) approaches. The goal of this work is to compare several LC and MS approaches and expand chemical coverage by optimizing the techniques.
Description:
"Introduction Humans are exposed to a myriad of chemicals on a daily basis. Fast, accurate and comprehensive analytical methods are needed to assess chemical exposures and protect human health. Recent applications of high resolution mass spectrometry (HRMS) and non-targeted analysis (NTA) have demonstrated the breadth of compounds that are present in the environment and living organisms. It has proven challenging, however, to confirm detected chemicals, and understand the chemical space limitations of the methods without extensive controlled experiments. To better assess NTA methods as tools for exposomics research, the US EPA’s Non-Targeted Analysis Collaborative Trial (ENTACT) was initiated. Methods Ten different ENTACT mixtures were prepared using ~1200 chemicals from EPA’s ToxCast program. ENTACT mixtures were analyzed using both positive and negative mode HRMS with atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). Mixtures were further evaluated across two chromatographic methods: one using a C8 column with methanol as the organic modifier, and the other using a C18 column with acetonitrile. Preliminary Data ESI vs. APCI: The experiment comparing ionization sources showed that some compounds prefer a specific ionization source, with 193 correctly identified via APCI, 746 via ESI, and 104 via both methods. Given these findings, we conclude that complementary approaches, combing both APCI and ESI, should be routinely used for exposomics studies. These results are now being used to predict the ionization behavior of untested chemicals to improve the chances of applying successful methods. Models based on these data are further being used to select across tentatively identified candidate structures in various NTA applications. While it is easy to assume that formation of the [M+H]+ is the predominant ionization mechanism, [M]+. formation was observed to be significant in APCI data interpretation. The results of this research highlight the need to carefully interpret HRMS data. C8/Methanol vs. C18/Acetonitrile: By changing the chemistry of the column packing material, increased interaction of the analytes with the column was observed, minimizing elution of analytes right after void volume. Furthermore, general improvement in ionization efficiency, peak shape, and analyte signal-to-noise ratio was achieved by switching the organic modifier from methanol to acetonitrile. This in turn, enhanced the number of compounds that were identified with high confidence based on MS-only and MS/MS information and database matching. For one of the mixtures, the blinded true positive rate went from 13% to 42% by switching the analysis from the C8/Methanol to the C18/Acetonitrile method. Novel Aspect ENTACT uses ~1200 compounds with varying physico-chemical properties to allow comparison of ionization and separation modes for NTA methods."
