Detection of methyl isocyanate in air with the use of hand-held ion mobility spectrometers

Abstract

Methyl isocyanate (MIC), CH₃NCO, is a relatively simple molecule, but ion mobility spectra derived from studies of this molecule are complex. MIC is known to polymerize, which would lead one to expect that proton-bound monomer, proton-bound dimer, and even larger proton-bound ions could be observed. Indeed, this is the case, and a number of other species can also be observed. In this case headspace above a relatively fresh (i.e., recently purchased) MIC sample was analyzed, and numerous peaks were observed in a single spectrum. Peak identities and intensities were, of course, concentration dependent. Over a range of concentrations, as many as 16 peaks were observed. IMS systems used for these studies included chemical agent monitors (both water and acetone chemistry), a miniaturized hand-held IMS device (Mini-IMS) and an IMS-MS/MS instrument. Although ion mobility spectra are complex, it has been shown that hand-held IMS devices can be useful for detecting or monitoring airborne concentrations of this toxic and hazardous compound. IMS/MS/MS experimentation yielded some mass identifications, and possible ion compositions are proposed. Reduced ion mobility of H⁺(CH₃NCO)(H₂O)_n was tentatively determined to be 1.91±0.02 cm₂ / V s. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1: 285–294, 1997