Flow-Optimized Model for Gas Jet Desorption Sampling Mass Spectrometry

Thermal gas jet probes, including post-plasma desorption/ionization sources, have not been studied using computational fluid dynamics (CFD) models, as have other ambient mass spectrometry sampling techniques. Two systems were constructed: a heated nitrogen jet probe to establish practical bounds for a sampling/transmission experiment and a CFD model to study trajectories of particles desorbed from a surface through optimization of streamlines and temperatures. The physical model configuration as tested using CFD revealed large losses, transmitting less than 10% of desorbed particles. Different distances between the desorption probe and the transport tube and from the sample surface were studied. The transmission improved when the system was very close to the sample, because the gas jet otherwise creates a region of low pressure that guides the streamlines below the inlet. A baffle positioned to increase pressure in the sample region improves collection efficiency. A Lagrangian particle tracking approach confirms the optimal design leading to a transmission of almost 100%.