Characterisation of the phosgene response of a membrane inlet 63Ni ion mobility spectrometer

Abstract

A membrane inlet ⁶³Ni ion mobility spectrometer interfaced to a quadrupole mass spectrometer with permeation, exponential dilution approaches and syringe-based systems were used to characterise the ion mobility spectrometry (IMS) response to phosgene in dry air (water concentration less than 16.5 mg m⁻³). Phosgene produced a principle product ion in the negative mode with a reduced mobility of 2.16 cm² V⁻¹ s⁻¹, with an unresolved artefact at higher concentrations having a reduced mobility of 2.32 cm² V⁻¹ s⁻¹. The limit of detection of the system with a membrane inlet fitted was estimated to be less than 1 mg m⁻³, with an upper limit to the dynamic range of 32 mg m⁻³. Mass spectrometric data indicated the existence of [(H₂O)_nCl]⁻, [(H₂O)_nCl₂]⁻; [(H₂O)_n(O₂)Cl]⁻; [(H₂O)_n(O)Cl]⁻; and, [(H₂O)_n(CO₂)Cl]⁻. The existence of two possible mechanisms for product ion formation is proposed: dissociative electron capture, as well as hydrolysis followed by electron capture. The effect of water contamination of the drying media within the ion mobility spectrometer was also investigated, and the effects were similar to those observed previously with studies on chlorine. Reduced mobility of the product ions was observed to decrease with increasing water contamination of the drying media used within the instrument, while limits of detection increased slightly to less than 2.4 mg m⁻³, with no significant effect on dynamic ranges of response or resolution. Preliminary results also indicated a positive mode response for phosgene, albeit at significantly higher concentrations to those observed in the negative mode.