Trace Analyses of Arsenic in Drinking Water by Inductively Coupled Plasma Mass Spectrometry:  High Resolution versus Hydride Generation

A magnetic sector inductively coupled plasma mass spectrometer (ICPMS) was applied to the determination of arsenic in drinking water samples using standard liquid sample introduction in the high-resolution mode (M/ΔM = 7800) and hydride generation in the low-resolution mode (M/ΔM = 300). Although high mass resolution ICPMS allowed the spectral separation of the argon chloride interference, the accompanying reduction in sensitivity at high resolution compromised detection and determination limits to 0.3 and 0.7 μg/L, respectively. Therefore, a hydride generation sample introduction method, utilizing a new membrane gas−liquid separator design, was developed to overcome the chloride interference. Due to the high transport efficiency and the 50−100 times higher sensitivity at M/ΔM = 300, the HG-ICPMS method resulted in an over 2000-fold increase in relative sensitivity. The routine detection and quantification limits were 0.3 and 0.5 ng/L, respectively. The results for both methods applied to the analysis of over 400 drinking water samples showed very good agreement at concentrations above 1 μg/L. For concentrations between 0.01 and 1 μg/L, only HG-ICPMS provided accurate quantitative results. Membrane desolvation, mixed-gas plasmas, and the addition of organic solvents for the reduction of the ArCl+ interference were also investigated and evaluated for trace As determination.