Determination of metal impurities in sulfamic acid by isotope dilution electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract

Metal impurities present at sub-ng g^–1–ng g^–1 levels in high-purity sulfamic acid reagents were determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) with sample introduction by electrothermal vaporization (ETV). Matrix constituents causing suppression and enhancement of analyte signals were removed from the sample introduction system at the pyrolysis stage before ETV-ICP-MS measurement. As the ETV device, both tungsten and graphite furnaces were employed. In graphite furnace ETV-ICP-MS, it was necessary to use a chemical modifier in order to enhance the signal sensitivity and to obtain a linear calibration graph. In tungsten furnace ETV-ICP-MS, a linear relationship between the analyte mass and the signal was achieved without the use of a modifier but the stability of the isotope ratio measurement was slightly poorer than that in graphite furnace ETV-ICP-MS. The relative standard deviations obtained by ETV-ICP-MS using both furnaces were 6–30%. The analytical results for two types of sulfamic acid reagent obtained by tungsten furnace ETV-ICP-MS agreed with those obtained by graphite furnace ETV-ICP-MS.