STUDY OF THE APPLICATION OF AIR-WATER FLOW-INJECTION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY FOR THE DETERMINATION OF CALCIUM IN STEELS

This paper describes a methodology for the determination of Ca, an imp ortant element in the process of steel making. Determination of Ca is typically problematic when using ICP-MS because of the Ar-40 interfere nce on the most abundant Ca isotope, In the present study the use of t he Ca-44 isotope for ICP-MS measurement was considered, To dissolve th e samples, a microwave digestion system was applied to guarantee the t otal dissolution of the Ca compounds, thus minimizing the sample prepa ration time, the amounts of reagents used ad the risk of contamination . Carbon and Si, normally present in steel samples, were eliminated by treatment with H2SO4 and HF to avoid (CO2)-C-12-O-16 and (SiO)-Si-28- O-16 isobaric interferences on the Ca-44 isotope, After matrix removal by the use of mercury cathode electrolysis, air-water PI-ICP-MS was u sed for the determination of Ca, Scandium, with an ionization potentia l and mass number close to those of Ca, was used as an internal standa rd for quantitative measurements, The operating parameters for air-wat er FI-TCP-MS were optimized with respect to signal peak height intensi ties, stability and matrix effect, The detection limit obtained was 0. 6 mu g g(-1) and the RSD value, calculated from ten replicates of a 20 0 mu l injection of a 50 mu g 1(-1) Ca solution spiked with 2 mu g 1(- 1) of Sc, was 0.7%. Data are presented for four certified reference st eel: materials: JSS 169-5 and 171-5, from Japanese Standards of Iron a nd Steel; and ECRMs 195-1 (Cr-Ni-steel) and 096 (low-S, low-Ca steel), from the Bureau of Analysed Samples.