Infrared Detection of the Nerve Agent Sarin (Isopropyl Methylphosphonofluoridate) in Water Using Magnesium Oxide for Preconcentration

Abstract

Detection of the nerve agent Sarin is investigated by using diffuse reflectance infrared spectroscopy with magnesium oxide (MgO) as a preconcentrating medium. Magnesium hydroxide, produced from magnesium oxide and water, initially hydrolyzes the Sarin to isopropyl methylphosphonic acid (IMPA). The IMPA then reacts with magnesium hydroxide (a slightly soluble product of the addition of MgO to water) to form an insoluble salt. Gas chromatography mass spectrometry (GC-MS) analysis of the Sarin/water solution indicates hydrolysis of the Sarin after 5 min of addition of the Nantek MgO and within 15 min after addition of the Aldrich MgO. Capillary electrophoresis analysis of the same Sarin/water solution shows that approximately 30% of the IMPA produced by the Nantek MgO hydrolysis of Sarin is not detected in solution, while most of the IMPA produced by the Aldrich MgO is detected. The diffuse reflectance infrared (IR) spectrum of the IMPA/MgO sample clearly indicates the presence of IMPA for both the Nantek MgO and Aldrich MgO samples. Well-resolved bands for methylphosphonic acid (MPA) are also evident for the Nantek MgO/Sarin sample, while less resolved, weaker bands due to MPA are seen for the Aldrich MgO/Sarin sample. These data suggest that a significant percentage of the Sarin is hydrolyzed to MPA by using the Nantek MgO. A detection limit of 98 ppb (Aldrich MgO) and 170 ppb (Nantek MgO) Sarin in water is calculated on the basis of the band heights and signal-to-noise ratio.