Abundance and Impact of Doubly Charged Polyatomic Argon Interferences in ICPMS Spectra

Abstract

Doubly charged molecular ions of alkaline earth metals and argon could be identified as spectral interferences in an inductively coupled plasma mass spectrometer. These molecular ions were found to occur at abundances reaching about 10(-4) relative to the alkaline earth atomic ion abundances. They can thus substantially affect ultratrace analyses and, when present at similar concentration as the analyte elements, also isotope ratio measurements. For the case of Cu and Zn isotope ratio analyses, the same mass concentration of Sr was found to alter the measured (63)Cu/(65)Cu and (64)Zn/(66)Zn isotope ratios by -0.036‰ to -0.95‰ due to SrAr(2+), appearing at m/Q 63 and 64. BaAr(2+) can affect Sr isotope analyses, MgAr(2+) may impair S isotope ratio measurements, while CaAr(2+) may cause interference to Ca(+) isotopes. The abundances of the doubly charged molecular ions were higher than those of the corresponding singly charged species, which is in accordance with their generally higher bond dissociation energies. The relative abundances were found to depend significantly on the inductively coupled plasma (ICP) operating conditions and generally increase with increasing carrier gas flow rates or lower gas temperature of the ICP. They also increase by about an order of magnitude when a desolvated aerosol is introduced to the ICP.

Spectroscopic characterization of a thermodynamically stable doubly charged diatomic molecule: MgAr2+

“…[31][32][33][34][35] It appears as an undesirable species in inductivelycoupled-plasma mass spectrometry and complicates the chemical analysis of S isotopes. 34,35 From the analysis of the density of MgAr 2+ at different plasma temperatures, Hattendorf et al could estimate the ground-state dissociation energy to be in the range between 124 and 130 kJ mol À1 . 34 In addition, Gardner et al 36 have characterized the electronic and vibrational structure of MgAr 2+ in high-level ab initio quantum-chemical calculations.…”

Particle generated spectral interferences in single particle ICP-MS: a roadblock to accurate nanometrology

“…However, an increase in nebulizer flow rate also results in a shorter duration of the molecules/ions in the plasma, which leads to increased oxide formation, and decreased double charge formation. 24,25 This is reflected in an increased signal observed for all isotopes monitored, as a result of increased transport into the plasma with increasing nebulizer flow rate (Table S5†). Interference formation was also affected, with an increase in the fraction of oxides ( 160 Gd increases from 1.8 to 5.3%) and a decrease in the fraction of doubly charged ions ( 72 Ge decreases from 2.9 to 1.9%) measured as nebulizer gas flow rate increased from 0.7 to 0.86 L min −1 .…”

Material Screening with Mass Spectrometry

“…Doubly charged ions were found to depend significantly on the inductively coupled plasma operating conditions and generally increase with increasing carrier gas flow rates. They also increase by about an order of magnitude when a desolvated aerosol is introduced to the ICP [20].…”