Quick Determination of Fourteen Rare Earth Elements in Powdered Refractory Materials Using Electrothermal Vaporization with Detection by Inductively Coupled Plasma Optical Emission Spectrometry

The determination of rare earth elements (REEs) in refractory materials by inductively coupled plasma (ICP) spectrometry with conventional sample introduction using pneumatic nebulization requires the dissolution of these samples, which is difficult. This work presents an optimized method using electrothermal vaporization (ETV) coupled to ICP optical emission spectrometry (OES) for the direct determination of REEs in refractory geological materials. Solid sampling eliminates the dissolution step, thereby increasing sample throughput. Furthermore, the small sample mass required with ETV allows faster analysis with greater sensitivity than with nebulization by eliminating the dilution inherent to dissolution and introducing more sample into the plasma compared to nebulization. Point-by-point internal standardization with an argon emission line compensates for the visible sample loading effect on the plasma. Multivariate optimizations of the carrier, bypass, and CF4 reaction gas flow rates, along with optimization of the pyrolysis temperature and cooling time between the pyrolysis and vaporization steps, enhanced analyte signals by 2.9-11 times compared to a previous ETV-ICPOES method for the analysis of slag. Adding at least 30 μL of high-purity water to the graphite boat containing solid samples enhanced sensitivity by 61% on average and enabled external calibration using standard solutions, which provided accurate results for 14 REEs (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tm, Y, and Yb). In contrast, only REEs with certified concentrations in the CRMs encompassing those in the sample could be determined by using CRMs for external calibration.