Roles of collisional dissociation modalities on spectral composition and isotope ratio measurement performance of the liquid sampling – atmospheric pressure glow discharge / orbitrap mass spectrometer coupling

Abstract

Coupling of the liquid sampling – atmospheric pressure glow discharge (LS-APGD) ionization source with Orbitrap mass spectrometers has demonstrated tremendous success in regards to isotope ratio (IR) measurements. Isotope ratios from a wide variety of analytes have been measured, with a primary focus on the 235U/238U measurement, yielding IR measurement accuracy and precision that meets international targets. Orbitrap mass spectrometers are not commonly associated with either elemental analysis or isotope ratio measurements. Understanding sources of IR errors and imprecision which arise from both the LS-APGD ionization source and the Orbitrap system itself can assist with enhancing measurement figures of merit. Because a variety of solvent related species are generated in the LS-APGD, the preponderance of those species in the orbitrap analyzer affects the recoveries and IR qualities for target analytes. In this work, the effects of the collisional dissociation of solvent-related species are investigated as a source of variability in IR measurements. Additionally, the quadrupole band-pass filter used in the ThermoScientific Q Exactive Focus is investigated for its transmission properties along with the effects of the transmission window on IR accuracy and precision. With these considerations, updated IR measurements are presented for a few analytes, with measurement precision never exceeding 0.71% RSD, and going down to a level of 0.05% for diverse species. It is expected that these considerations will inform how IR measurements should be taken on this platform, with lessons that may be applicable to other instruments.