Isotope Ratio Measurements of Iron, Bromine and Selenium in Aqueous Solutions by Helium Microwave-Induced Plasma Mass Spectrometry

Abstract

A helium microwave-induced plasma (MIP) at atmospheric pressure has been generated in a modified TM₀₁₀ Beenakker cavity. The MIP was coupled with a laboratory-built mass spectrometer used to measure the isotope ratios of Fe, Br and Se, which are not easily measured by an Argon inductively coupled plasma (ICP) source, due to spectral interference. In helium MIP, the analyte signal intensities are maximum when a torch edge is sampled; unidentified molecular ions appear across the entire mass range when the torch center is sampled. The measured isotope ratios agree quite well with the accepted values, and the detection limits are in the low-ppb range.