Atmospheric pressure photoionization – High-field asymmetric ion mobility spectrometry (APPI-FAIMS) studies for on-site monitoring of aromatic volatile organic compounds (VOCs) in groundwater

A continuously operating system for monitoring groundwater contamination by aromatic VOCs has been developed. For this purpose, a novel gas-water separation unit was to be used in combination with APPI-FAIMS. The gas-water separation unit successfully reduced the humidity in the sample flow to ≤1.6 ppmv prior to analyte ionization. Initially, toluene was selected as a model aromatic VOC. The quantitative response of toluene, as a single VOC in water (LOD <1 mg L−1), was used to investigate the feasibility of the monitoring system and the effect of humidity on the signal produced by the APPI-FAIMS. With humidity increase (up to 400 ppmv) an increase of the toluene signal for about 30% was observed, including the possible formation and detection of water clusters and toluene-water clusters. Similar effects were noted in the case of benzene. However, for the detection of single contaminants such as indane and trimethylbenzenes (TMBs) this was not observed even at relative high humidity (500 ppmv). Additionally, on-site, continuous, groundwater monitoring of the aromatic VOCs contamination was carried out successfully with the gas-water separation APPI-FAIMS at low humidity (0.3–1.6 ppmv) allowing simplified monitoring of a specific, total aromatic VOCs signal in groundwater.