Improving VOC Quantitation Methodology Using Selected Ion Flow Tube Mass Spectrometry

Abstract

Measuring initial volatile organic compound (VOC) concentrations (c₀) is an important first step in the development of mass-transport models in diverse fields, including indoor air quality, food packaging, and biocompatibility. Here, we highlight a previously overlooked methodological issue with techniques employing a re-equilibration step and present an improved experiment based on selected ion flow tube mass spectrometry (SIFT-MS). Specifically, the overlooked aspect of these techniques is unaccounted for VOC loss from the sample during the headspace flushing step. Diffusion modeling indicates that this loss can be significant even when the flushing time is a fraction of the diffusion time. To experimentally demonstrate the impact of mass loss during flushing, we compare the initial concentrations of several volatile methyl siloxanes in Sylgard 184 obtained from multiple headspace extraction (MHE) and a real-time extraction method: TD-SIFT-MS. We find that the TD-SIFT-MS method reports higher c₀ values than MHE with a lower temperature dependence. A technique like TD-SIFT-MS is advantageous because it does not require numerous lengthy equilibration steps and offers full awareness of the system dynamics over the course of the experiment.