Halo-Shaped Flowing Atmospheric Pressure Afterglow: A Heavenly Design for Simplified Sample Introduction and Improved Ionization in Ambient Mass Spectrometry

Abstract

The flowing atmospheric pressure afterglow (FAPA) is a promising new source for atmospheric pressure, ambient desorption/ionization mass spectrometry. However, problems exist with reproducible sample introduction into the FAPA source. To overcome this limitation, a new FAPA geometry has been developed in which concentric tubular electrodes are utilized to form a halo-shaped discharge; this geometry has been termed the halo-FAPA or h-FAPA. With this new geometry, it is still possible to achieve direct desorption and ionization from a surface; however, sample introduction through the inner capillary is also possible and improves interaction between the sample material (solution, vapor, or aerosol) and the plasma to promote desorption and ionization. The h-FAPA operates with a helium gas flow of 0.60 L/min outer, 0.30 L/min inner, applied current of 30 mA at 200 V for 6 watts of power. In addition, separation of the discharge proper and sample material prevents perturbations to the plasma. Optical-emission characterization and gas rotational temperatures reveal that the temperature of the discharge is not significantly affected (< 3% change at 450K) by water vapor during solution-aerosol sample introduction. The primary mass-spectral background species are protonated water clusters, and the primary analyte ions are protonated molecular ions (M+H+). Flexibility of the new ambient sampling source is demonstrated by coupling it with a laser ablation unit, a concentric nebulizer and a droplet-on-demand system for sample introduction. A novel arrangement is also presented in which the central channel of the h-FAPA is used as the inlet to a mass spectrometer.

Ambient ionization and direct identification of volatile organic compounds with microwave‐induced plasma mass spectrometry

“…[40] Water cluster ions promoted efficient proton-transfer ionization, yielding protonated molecular ion [M + H] + . The peaks at m/z = 36, 53 and 72 were assigned to (NH 3 3 ]H + , which can result in the formation of ammonium adduct ions [M + NH 4 ] + . Ammonium adduct ions could be another proton source.…”

Investigation and Applications of In-Source Oxidation in Liquid Sampling-Atmospheric Pressure Afterglow Microplasma Ionization (LS-APAG) Source

“…In recent years, numerous plasma-based ionization techniques under atmospheric pressure or ambient conditions [13][14][15][16][17] are emerging as powerful tools for rapid analysis of diverse analytes, which can also employ Breactive^plasma as the ionization reagent to initiate various types of reactions [18][19][20][21], including conventional chemical reactions, electrochemical or photochemical reactions, and gas-phase ion-molecule reactions. In-source oxidation, as a common reaction in the ionization process, should be avoided in routine analysis but has been successfully applied in structural analysis [7].…”

Microplasma-based flowing atmospheric-pressure afterglow (FAPA) source for ambient desorption-ionization mass spectrometry

“…The μ-FAPA is based on the previously described halo-FAPA (h-FAPA) design [18], but miniaturized in order to take advantage of microplasma properties. A photograph and schematic diagram of the µ-FAPA source are shown in Services, Ringoes, NJ), with 2 mm of the anode exposed beyond the alumina tube.…”

“…The FAPA source utilizes the effluent (afterglow) from a DC helium glow discharge to thermally desorb and ionize samples. Originating from the atmospheric-pressure glow discharge (APGD) [16], the FAPA has been introduced in several forms, including a pinto-plate [8] configuration, a pin-to-capillary [17] geometry, and a concentric-electrode arrangement [18]. Applications of FAPA-MS include detection of illicit drugs [19] and drug metabolites [20], imaging [19], and polymer fingerprinting [21], among others.…”