Photoionization ion mobility spectrometry (PIMS) hyphenated with gas chromatography (GC) exhibits outstanding selectivity and high sensitivity in the detection of trace volatile organic compounds (VOCs). Its analytical performance is considerably affected by the interface between the GC and the ionization chamber of the PIMS. The sensitivity of the PIMS is reliant on the overlap of photoionization optical fields with the effluent from the GC, which is also affected by the gas flow in the ion mobility spectrometer. In this work, a computational model based on multiphysics dynamic convolution has been developed to evaluate the spatial concentration distribution of sample gas on the photoionization yield of PIMS. The simulation results indicate that lateral injection of GC capillary column into the gas flow of the ion mobility spectrometer could enhance the sensitivity by increasing the overlap of effluent and the VUV light in the ionization region of PIMS. The optimal capillary insert depth was increased when decreasing the carrier gas flow rate, which was confirmed by numerical simulations and experimental measurements. The optimal insert depth was 7.5 mm (the central axis of the ionization source) under conditions of a carrier gas flow rate of 15 mL·min-1, the limit of detection for aromatic compounds was reached 2.5 ppbv, achieving a 4-fold improvement of sensitivity over zero insertion. The GC-PIMS was tested to assess the VOCs emissions from spray-coated surfaces, and trace levels of toluene (45 μg·m-3) and xylene (60 μg·m-3) were still detectable even 14 days later, which highlights the potential of the GC-PIMS apparatus for monitoring trace environmental pollutants.
Song et al. (Tue,) studied this question.