Development of an\nUltrasonic Nebulization System for\nan Inverse Low Temperature Plasma Ionization Source

An effective nebulization and evaporation of a liquid\nsample, like\nin liquid chromatography, mass spectrometry (LC-MS) couplings, is\nan essential requirement for the ionization of analyte molecules in\nthe gas phase by, for example, atmospheric pressure chemical ionization\n(APCI) or the novel low temperature plasma (LTP)-based ion source.\nThese LTP-based ion sources have recently gained interest in the field\nof atmospheric pressure ion sources, as they can cover a wide range\nof polarity and molecular mass. They can be used in combination with\nseparation techniques like liquid chromatography or used as an ambient\nion source. However, commercial nebulizer systems are of course not\nconstructed to fit to home-built LTP-based ion sources, and this was\none incentive to develop a new nebulization system. Instead of an\natmospheric pressure chemical ionization (APCI) nebulizer, two commercial\nnebulizers were disassembled and remodeled to be used as nebulizing\nsystems in an LC-MS setup using an LTP-based ion source. Based on\nthese results, a novel nebulizer system was subsequently developed.\nTo further improve the degree of ionization, cones to focus the LC\neluent spray on the plasma region, heating applications, and auxiliary\nnitrogen gas for dispersion of the solvent droplets were implemented.\nThe LOD that could be calculated via the rule of three resulted in\nan average of 2.0 μg/L for the APCI-nebulizer and 41 μg/L\nfor the USN. Both could be reduced to 1.4 and 18 μg/L, respectively,\nby using a TPI-configuration instead of an iLTP. The linearity was\nequally good for both types of nebulization devices. The final nebulizer\ncould also be operated with a high water content and flow rates higher\nthan those of the two previous ones, indicating an important improvement\nstep.