A rapid and sensitive IC-ICP-MS method for determining selenium speciation in natural waters

Abstract

Selenium (Se) is an element monitored by water quality agencies worldwide. The challenge of assessing its presence in aquatic systems is its low concentrations (parts per trillion) and the need for determining its chemical speciation. A method was developed using an ion chromatograph (IC) paired with a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) equipped with a hydrogen reaction cell to provide analysts with a rapid and sensitive method to measure Se speciation with suitable accuracy and precision. The Se species selenite (SeIV) and selenate (SeVI) were separated within a 5 min span using dilute nitric acid as a mobile phase in a step-wise gradient (50–400 mmol L−1) and quantified using 80Se isotope that yielded low limits of detection (<10 ng L−1). Spectral interference from plasma generated diatomic argon ions (40Ar2+; m/z = 80) on 80Se was eliminated by hydrogen gas (H2) in the reaction cell. Polyatomic 79Br1H+ (m/z = 80) did not interfere with 80Se for quantification of common aquatic Se species (SeVI and SeIV) due to different column retention times. Two organic species (methylselenocysteine and selenomethionine) commonly found in aquatic and terrestrial plant tissues were also tested to rule out possible chromatographic interference and explore the potential application to biological samples. Urban rainwater and Canadian river water samples were analyzed for Se species to demonstrate the applicability of the method. Owing to its ability to rapidly determine Se species in water samples at environmentally relevant concentrations, the method may be useful for monitoring agencies to routinely measure Se species in freshwater aquatic systems.