Ambient Ion Focusing from a Field-Free Region to a Detector: Enhanced Signal for Explosives and Drug Detection with Mass Spectrometry

This study demonstrates ion focusing at ambient pressure and increased ion signal by creating a voltage difference from a field-free region to a detector, thereby improving the detection of chemicals such as explosives and drugs. At ambient pressure, ion loss and the resulting signal reduction pose challenges that limit detection sensitivity in analytical instruments. Techniques to increase sensitivity, such as atmospheric flow tube-mass spectrometry (AFT-MS), extend ion-molecule reaction times but result in significant overall ion loss due to diffusion. Ion manipulation techniques, though challenging at ambient pressure, can mitigate these losses by concentrating ions toward the detector inlet. Using SIMION, electric fields and ion trajectories were modeled with a voltage difference applied between a flow tube and a detector, revealing the potential for ion focusing at ambient pressure. Experimentation with an atmospheric flow tube, a mass spectrometer, and Faraday plate detectors was used to measure ion beam profiles across varying flow rates, tube diameters, and voltage differences. Application of a voltage difference effectively directed ions to the axial center of the flow tube, narrowed ion beam width, and increased signal intensity by 5 to 10 times for mass spectrometer and Faraday plate detectors, respectively, compared to conditions without a voltage difference. This ion-focusing approach shows promise for improving sensitivity in ambient-pressure instruments. This technique has the potential to enhance detection levels in security and forensic applications, with particular benefits for field-portable devices that can be used at checkpoints to identify explosives and drugs.