Direct determination of trace impurities in niobium pentaoxide solid powder with slurry sampling fluorination assisted electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract

A method of fluorination assisted electrothermal vaporization inductively coupled plasma mass spectrometry (FETV-ICP-MS) was developed to directly determine the trace impurities in niobium pentaoxide solid powder in which a poly(tetrafluoroethylene) (PTFE) emulsion was used as fluorinating modifier to promote the vaporization of refractory elements from a graphite furnace and to avoid the formation of thermally stable carbides. The solid sample was introduced into the graphite furnace in the form of slurry without any chemical pretreatments. The electrothermal vaporizer device was connected to the ICP system by a laboratory-built interface, and the flow rates of sample carrier gas and auxiliary carrier gas were optimized experimentally. The potentially polyatomic interferences resulting from the pyrolysates of PTFE were evaluated. A new method by stepwise diluting the sample matrix is proposed for investigating the matrix effect and the results showed that no obvious matrix effect was observed with a sample matrix (Nb₂O₅) concentration of less than 200 mg L⁻¹. Under the optimal conditions, the absolute limits of detection for FETV-ICP-MS determination of Ta, Ti, Cr, W, Ni, Cu and Mn were in the range of 0.026–1.1 pg. For one analysis run, only 0.002 mg of Nb₂O₅ sample was required. The proposed method has been applied to determining the trace impurities in Nb₂O₅ powder, and both the results obtained from the external calibration method and the standard addition method were in a good agreement with those obtained by conventional nebulization ICP-MS.