The G- and V-series nerve agents are organophosphorus based compounds that have unique chemical structures with a variety of pendant organic groups that may be changed to give rise to thousands of unique molecular structures. Identification of these compounds in the field is paramount for remediation efforts and remains a considerable challenge. Typically, high resolution Nuclear Magnetic Resonance (NMR) is employed to identify small organic molecules but the high magnetic field (tesla (T) regime) super-conducting NMR magnets are not suitable for use as fieldable or portable units. Reducing the magnetic field, while more feasible for a fieldable unit, also reduces the chemical shift information, which is the primary metric used to identify small molecules by NMR. Modern desktop NMRs, operating in the 1 to 1.5 T (43 and 60 MHz for proton) regime, using permanent magnets, retain some chemical shift and J-coupling information and are considered portable. In attempting to move into the milli-Telsa (mT) regime (100-500 mT or lower) to reduce the weight and cost of a permanent magnet system, decreased sensitivity and signal broadening obscures the chemical shift and J-coupling information. Upon reaching the micro-tesla (µ-Tesla) ultra-low magnetic field regime, <i>i.e.</i> Earth’s Magnetic field (50 µT), all chemical shift information is lost; however, since J-coupling is magnetic field independent, new spectral information becomes available through intramolecular, through-bond heteronuclear and homonuclear J-coupling interactions. In this regime, unique "J-coupled" spectra provide distinct structural fingerprint signatures due to heteronuclear J-coupling. Here, we employ Earth's magnetic field (50 µ-Tesla ultra-low magnetic field regime) to leverage J-coupled spectroscopy and identify CWA surrogates, precursors, and decomposition products using a fieldable NMR spectrometer. Experimental J-coupled spectra show close agreement to theoretically calculated J-coupled spectra where observed J-coupling constants at ultra-low magnetic field, as expected, match ones measured at high magnetic field. Furthermore, the experimental and calculated J-coupled spectra of several G-agent hydrolysis products, analogs, and surrogates show unique J-coupled spectroscopic signatures indicating the feasibility of using such an ultra-low magnetic field NMR system for the detection, identification, and quantitation of Chemical Warfare Agents.

Identification of organophosphorus chemical warfare agents (CWAs), precursors, and decomposition products with a fieldable NMR spectrometer using earth's magnetic field

2019 Fall National Meeting

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