DETERMINATION OF METAL IMPURITIES IN SULFAMIC ACID BY ISOTOPE-DILUTION ELECTROTHERMAL VAPORIZATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

Metal impurities present at sub-ng g(-1)-ng g(-1) levels in high-purit y sulfamic acid reagents were determined by isotope dilution inductive ly coupled plasma mass spectrometry (ID-ICP-MS) with sample introducti on by electrothermal vaporization (ETV). Matrix constituents causing s uppression and enhancement of analyte signals were removed from the sa mple introduction system at the pyrolysis stage before ETV-ICP-MS meas urement. As the ETV device, both tungsten and graphite furnaces were e mployed. In graphite furnace ETV-ICP-MS, it was necessary to use a che mical modifier in order to enhance the signal sensitivity and to obtai n a linear calibration graph. In tungsten furnace ETV-ICP-MS, a linear relationship between the analyte mass and the signal was achieved wit hout the use of a modifier but the stability of the isotope ratio meas urement was slightly poorer than that in graphite furnace ETV-ICP-MS.- The relative standard deviations obtained by ETV-ICP-MS using both fur naces were 6-30%. The analytical results for two types of sulfamic aci d reagent obtained by tungsten furnace ETV-ICP-MS agreed with those ob tained by graphite furnace ETV-ICP-MS.