Dual-technique assay for the analysis of organophosphorus compounds for environmental and chemical defense applications

Abstract

Forensic and environmental sciences often rely on chromatographic separations coupled to mass spectrometry to detect contaminants in complex matrices. However, these methods require lengthy analysis times and sample preparation that is not suitable for analysis in the field. In this work, two analytical methods were combined that are known for their potential for portable analysis. The ambient ionization technique, paper spray mass spectrometry (paper spray-MS) was coupled to paper-based surface enhanced Raman spectroscopy (pSERS) to detect toxic organophosphorus molecules from the same substrate, with a total analysis time of less than five minutes. The coupling of these techniques presents a potential for portable Raman screening followed by MS confirmation in a field-forward laboratory. A cartridge insert was designed and 3D printed to facilitate the sample collection and analysis for PS-MS and pSERS. Three chemical warfare agent simulants: dimethyl methylphosphonate (DMMP), diethyl phosphoramidate (DEPA), and diisopropyl methylphosphonate (DIMP) were included in the method due to having similar chemistries to G- and V-series chemical warfare agents (CWAs). Organophosphorus pesticides, malathion and dichlorvos, with similar mechanisms of action to the CWAs, were also included in the method. Because CWAs quickly degrade in the environment, the CWA hydrolysis products, ethyl methylphosphonic acid (EMPA), isopropyl methylphosphonic acid (IMPA), pinacolyl methylphosphonic acid (PinMPA), methylphosphonic acid (MPA), 2-Diethylaminoethanethiol (EDA), and 2-Diisopropylaminoethanethiol (IDA) were also studied. A mixture of the analytes was used to create calibration curves using the dual-polarity, PS-MS method with sub-ng to low ng limits of detection. A dilution series, spanning 3 orders of magnitude, was made using pSERS, also with low ng limits of detection. These experiments show the potential and feasibility for PS-MS coupled to pSERS to be used to rapidly, screen and confirm the presence of organophosphorus molecules, in complex matrices, with portable instrumentation.