Determination of Trace Rare Earth Elements in Soils and Sediments by Inductively Coupled Plasma-Mass Spectrometry with Microwave Digestion

A method to determine concentrations of 15 rare earth elements in soil and sediments by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) with microwave digestion is reported in this paper. Experimental conditions such as sample dissolution reagents, microwave digestion procedure, standard solution preparation, mass spectrum interferences and internal standards were studied. The samples were dissolved completely by the addition of HF acid. The dissolving rate of rare earth elements (REEs) was improved by using mix HNO₃-HF-H₂O₂ reagent. The interference effects among REEs can be minimized by using matched calibration solutions with a similar composition to soil and sediments. Polyatomic ions inferences were calibrated by equivalent concentrations, calculated by the measured ratios of MO⁺/M and MOH /M of individual La, Ce, Pr, Nd and Ba solution. ¹⁰³Rh was selected as an internal standard to calibrate the analytical signal drift. The detection limits for the method were 1.2-7.1 ng/g, the relative standard deviation (RSD, n=6) was less than 5.3% and recoveries were 86.1%-110.1%. The accuracy and precision of the method were validated by reference materials and the results were consistent with the certified values. This method is simple, rapid, has good reproducibility and wide linearity, all of which meets the requirements for the analysis of large batches.