High frequency air monitoring by selected ion flow tube-mass spectrometry (SIFT-MS): Influence of the matrix for simultaneous analysis of VOCs, CO2, ozone and water

Abstract

Selected Ion Flow Tube–Mass Spectrometry (SIFT-MS) with both positive (H3O+, O2•+ and NO+) and negative precursor ions (O•−, OH−, O2•−, NO2−and NO3−) was successfully used for the simultaneous monitoring at the ppbV level of VOCs together with high CO2, water or ozone concentration in complex matrixes. The use of negative precursor ions SIFT-MS allows the detection of carbon dioxide, water and ozone, while increasing the selectivity for VOCs. The complete understanding of all the possible ion-molecule reactions led to the development of accurate quantification methods, independent of any variation of the air matrix composition. For instance, due to the low reactivity of carbon dioxide with OH−, its correct monitoring implies considering not only the reaction of the analyte with the precursor ion, but also with their more reactive hydrates.The results obtained by the developed method were validated on certified standard concentrations. This new SIFT-MS analysis method was further applied to an actual case for the evaluation of indoor air purifying devices and agreed with less convenient and more time-consuming standard analysis methods. It was thus demonstrated for the first time that the simultaneous high frequency, single run and direct monitoring of VOCs, carbon dioxide, water and ozone gave a complete overview of the device operation and of the matrix evolution.