Transportable real-time single-particle ion trap mass spectrometer

Abstract

A transportable ion trap mass spectrometer for real-time detection and characterization of individual airborne particles was constructed by minimal modification of a commercial ion trap mass spectrometer. A blank flange was replaced with a flange containing an aerodynamic lens based inlet, light scattering detection optics and ablation/ionization laser optics. Four holes were drilled into the ring electrode. Timing electronics boards running off of in-place power systems were added and integrated with the existing software. The modified mass spectrometer and laser system was packaged in a rugged wheeled frame for easy transport. Particles entered the instrument through a 100μm orifice and were passed through an aerodynamic lens system that produced a well-collimated particle beam over a wide range of sizes. The particle beam passed through a skimmer into the main chamber where individual particles were optically detected and sized with two focused 532nm diode lasers on their way to the ion trap. When the particles reached the center of the trap, they were ablated and ionized with a focused 266nm laser. The nascent ions were then mass analyzed using standard ion trap techniques, including tandem mass spectrometry. Each detected particle was characterized with a mass spectrum and an aerodynamically determined particle size. Careful design minimized the weight and size of the instrument to 104kg and 69×71×76cm, with power consumption less than 1.5kW. Tandem mass spectrometry was demonstrated for identification of ions through collision-induced dissociation (CID) up to mass spectrometry (MS).4 Unit mass resolution was observed in both the parent and CID mass spectra.