Accurate quantification of mercury in river water by isotope dilution MC-ICP-SFMS and ICP-QMS detection after cold vapour generation

Abstract

Precise and accurate determination of Hg in surface water is challenging due to volatilization and adsorption effects of Hg and low ng L⁻¹ concentrations. The aim of our study was to examine the parameters, which affect the uncertainty of Hg concentrations determined by CV-ICP-MS, employing isotope dilution analysis for accurate quantification. We used two different types of mass spectrometers (MC-ICP-SFMS and ICP-QMS) and further evaluated two widely used isotope dilution approaches to achieve accurate data with low uncertainties for ultra trace level Hg determination in surface water. Obtained LODs were significantly below 1 ng L⁻¹. Validated concentrations of Hg obtained in the new ground water reference material ERM-CA615 were in good agreement with the indicative value of 0.037 μg L⁻¹ (95% confidence interval, k = 2). A reduction in the propagated uncertainty was evident with CV-MC-ICP-SFMS and also by undertaking a mass bias drift correction during the measurement session with certified isotope ratio values as currently accepted by the IUPAC. We could demonstrate that accurate Hg quantification can be achieved with either multicollector or quadrupole detection within a level of uncertainty of 27%/52% (u_c, k = 2) down to 1 ng L⁻¹ and better than 2%/5% (u_c, k = 2) from 5 ng L⁻¹. Taking the advantages of matrix separation/pre-concentration obtained from CV sample introduction, the method allows quantifying Hg in surface water within the data quality requirements regarding the Water Framework Directive.