Abstract
Di-isopropyl methyl phosphonate (DIMP) has no major commercial uses but is a by-product or a precursor in the synthesis of the nerve agent sarin (GB). Also, DIMP is utilized as a simulant compound for the chemical warfare agents sarin and soman in order to test and calibrate sensitive IMS instrumentation that warns against the deadly chemical weapons. DIMP was measured from 2 ppb(v) (15 μg m(-3)) to 500 ppb(v) in the air using a pocket-held ToF ion mobility spectrometer, model LCD-3.2E, with a non-radioactive ionization source and ammonia doping in positive ion mode. Excellent sensitivity (LoD of 0.24 ppb(v) and LoQ of 0.80 ppb(v)) was noticed; the linear response was up to 10 ppb(v), while saturation occurred at >500 ppb(v). DIMP identification by IMS relies on the formation of two distinct peaks: the monomer M·NH(4)(+), with a reduced ion mobility K(0) = 1.41 cm(2) V(-1) s(-1), and the dimer M(2)·NH(4)(+), with K(0) = 1.04 cm(2) V(-1) s(-1) (where M is the DIMP molecule); positive reactant ions (Pos RIP) have K(0) = 2.31 cm(2) V(-1) s(-1). Quantification of DIMP at trace levels was also achieved by GC-MS over the concentration range of 1.5 to 150 μg mL(-1); using a capillary column (30 m × 0.25 mm × 0.25 μm) with a TG-5 SilMS stationary phase and temperature programming from 60 to 110 °C, DIMP retention time (RT) was ca. 8.5 min. The lowest amount of DIMP measured by GC-MS was 1.5 ng, with an LoD of 0.21 μg mL(-1) and an LoQ of 0.62 μg mL(-1) DIMP. Our results demonstrate that these methods provide robust tools for both on-site and off-site detection and quantification of DIMP at trace levels, a finding which has significant implications for forensic investigations of chemical agent use and for environmental monitoring of contamination by organophosphorus compounds.