Comparison of cryogenic and membrane desolvation for attenuation of oxide, hydride and hydroxide ions and ions containing chlorine in inductively coupled plasma mass spectrometry

Abstract

Conventional, cryogenic and membrane desolvation methods were compared with respect to sensitivity, MO⁺/M⁺ signal ratios and the aerosol gas flow rate required to maximize M⁺ and MO⁺ signals. Thorium was used to represent the actinides, which form relatively strong hydrides and hydroxides. The LaO⁺/La⁺ ratio is reduced from 0.24% with conventional desolvation to 0.08% with membrane desolvation and 0.01% with cryogenic desolvation. Membrane desolvation reduces ThH⁺ and ThOH⁺ 2-fold compared with conventional desolvation. Cryogenic desolvation attenuates ThH⁺ 7-fold and ThOH⁺ 20-fold compared with conventional desolvation. The three desolvation methods were also evaluated for the removal of ClO⁺ and ArCl⁺ for the determination of vanadium and arsenic at trace levels in the presence of chloride. The density of oxygen atoms is reduced as water vapor is removed, and chloride is also removed, presumably as hydrogen chloride. The concentration of vanadium in a urine standard reference material was determined by standard additions to be 7 ppb with cryogenic desolvation and 5 ppb with membrane desolvation. Analysis of several nasal wash samples using cryogenic and membrane desolvation yielded results that agreed within 5% for the two methods in all cases except for the sample with the highest V⁺ concentration.