Determination of trace rare earth elements in gadolinium aluminate by inductively coupled plasma time of flight mass spectrometry

An analytical methodology was developed for the precise quantification of ten trace rare earth elements (REEs), namely, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, and Tm, in gadolinium aluminate (GdAlO3) employing an ultrasonic nebulizer (USN)-desolvating device based inductively coupled plasma mass spectrometry (ICP-MS). A microwave digestion procedure was optimized for digesting 100mg of the refractory oxide using a mixture of sulphuric acid (H2SO4), phosphoric acid (H3PO4) and water (H2O) with 1400W power, 10min ramp and 60min hold time. An USN-desolvating sample introduction system was employed to enhance analyte sensitivities by minimizing their oxide ion formation in the plasma. Studies on the effect of various matrix concentrations on the analyte intensities revealed that precise quantification of the analytes was possible with matrix level of 250mgL−1. The possibility of using indium as an internal standard was explored and applied to correct for matrix effect and variation in analyte sensitivity under plasma operating conditions. Individual oxide ion formation yields were determined in matrix matched solution and employed for correcting polyatomic interferences of light REE (LREE) oxide ions on the intensities of middle and heavy rare earth elements (MREEs and HREEs). Recoveries of ≥90% were achieved for the analytes employing standard addition technique. Three real samples were analyzed for traces of REEs by the proposed method and cross validated for Eu and Nd by isotope dilution mass spectrometry (IDMS). The results show no significant difference in the values at 95% confidence level. The expanded uncertainty (coverage factor 1σ) in the determination of trace REEs in the samples were found to be between 3 and 8%. The instrument detection limits (IDLs) and the method detection limits (MDLs) for the ten REEs lie in the ranges 1–5ngL−1 and 7–64μgkg−1 respectively. •A mixture of H2SO4, H3PO4 and H2O was optimized for microwave digestion of GdAlO3.•With 250mgL−1 matrix concentration, reproducible analyte intensities were obtained.•Recoveries of ≥90% for all analytes were obtained.•Results by proposed method and IDMS for Eu and Nd, matched at 95% confidence level•The expanded uncertainty of the proposed was found to be 3–8% (at a coverage factor of 1σ).