Simultaneous Ultratrace Determination of Zr and Nb in Chromium Matrixes with ICP-Dynamic Reaction Cell MS

A dynamic reaction cell (DRC) has been used to minimize the formation of metal-argide ions in inductively coupled plasma mass spectrometry and applied to the determination of Zr and Nb in Cr-rich samples. The formation of ArCr+ species from the plasma gas and the sample matrix was reduced by ion molecule reactions inside a DRC of the ICPMS used. Hydrogen was used as reaction gas, and the efficiency in the reduction of ArCr+ was similar to that of other plasma-based polyatomic ions as reported in an earlier study. The formation of CrOx+ ions is enhanced when the DRC is operated in pressurized mode. Adjustment of the transmission properties of the band-pass quadrupole to reject precursor ions can be achieved without dramatic decrease of sensitivity but with a significant improvement in the signal/background ratio. Measurements in solutions containing concentrations of up to 2 g/L Cr showed that the determination of Nb and Zr is possible in the nanogram per liter range in such a matrix. The limits of detection for Nb and Zr in pure Cr metal have been estimated at 2 ng/g for Nb and 5 ng/g for Zr. Analysis of basaltic reference samples resulted in very good agreement with previously published data.