Membrane set up combined with photoionization-ion mobility spectrometer to improve analytical performance and avoid humidity interference on the determination of aromatics in gaseous samples

UV-ion mobility spectrometry (UV-IMS) is a reliable and inexpensive technique which allows efficient monitoring of BTX (benzene, toluene, m-xylene, o-xylene and p-xylene) in different air samples. Water molecules are unavoidably present in every on-field measurement affecting sensitivity and selectivity of the UV-IMS method. For this reason, the influence of humidity on the mobility spectra when measuring BTX is discussed here. Furthermore, a polydimethyl siloxane (PDMS) membrane assembled on an ad-hoc designed membrane holder coupled to UV-IMS was proposed for online measurement of analytes in humid gaseous samples without sample preparation/pre-treatment steps. The use of this membrane reduces the moisture of the gaseous sample before entering into the IMS, and the consequent distortion of the signal. The limit of detection (LOD) and the limit of quantification (LOQ) achieved with the method proposed were in the range of 0.49-1.21 mg L−1 and 1.63-4.03 mg L−1, respectively for all analytes. The precision of the method was evaluated in terms of repeatability and reproducibility obtaining values lower than 1.1% for drift time and 12.0% for peak height when the membrane was used coupled to the UV-IMS for all target analytes in the humidity range of 10-75% RH. Thus, BTX can be determined directly and quantified unequivocally with the membrane system in ambient air even at humid condition.