Simulations and experimental investigation of atmospheric transport in an ambient metastable-induced chemical ionization source.

Since its inception, Direct Analysis in Real Time (DART) has seen utility in a wide range of applications including chemical reaction monitoring, pharmaceutical screening, and forensic mass spectrometry. Despite the growing interest in DART applications, there has been limited research into the fundamental physiochemical phenomena affecting sampling, ionization, and atmospheric ion transport. Presented here are the first experimentally validated finite element method simulations of an ambient DART-type metastable-induced chemical ionization source. It was found that complex coupled fluid dynamics, heat transfer, and electrostatic phenomena within the sampling region determine the variability in ion transmission efficiencies affecting the overall sensitivity of analysis. Particle tracing plots of a circular acetaminophen tablet placed in various positions and orientations yielded insight into optimal sample placement and evidence for sweet spots conducive to better ion transport. Experiments in a wide range of electric field conditions were performed, finding that under optimum sample placement, sensitivity could be improved by as much as 128% if ion mobility contributions were minimized.