Coupling of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source with a commercial triple-quadrupole mass spectrometer

Abstract

While the LS-APGD microplasma has shown potential as an ionization source for elemental/isotopic/molecular species analysis, up to this point it has been used almost exclusively in conjunction with trapping-type mass analyzers. To this end, the LS-APGD has been coupled to a standard ThermoScientific TSQ Quantum Access MAX triple quadrupole mass spectrometer. This instrument is capable of affecting numerous MS/MS techniques as well as scanning for low mass elements which are not typically permitted in trapping-type MS instruments. The TSQ differs appreciably in how it may be implemented in tandem mass spectrometry versus triple quadrupoles becoming common in ICP-MS. For example, fragmentation methods such as collision-induced dissociation (CID) in Q2 and in-source CID can be affected to reduced background spectral contributions and remediate molecular interferences. With this new coupling, a thorough multi-parametric evaluation was necessary. This evaluation was performed by optimizing the analyte responses and signal-to-background ratios for Rb, Ag, Tl, and U as test elements. With the optimized conditions set, parent ion, product ion, and neutral loss scan methods were explored to observe the types of species being formed by the LS-APGD. While the primary impetus for using the triple quadrupole analyzer was to allow for detailed fundamental studies, LODs for the test elements were determined simultaneously, ranging from 0.99 to 38 ng mL⁻¹ for 50 μL injections (i.e., 0.05–2 ng absolute mass).