Determination of Rare Earth Elements in Soil and Sediments by Microwave Digestion-inductively Coupled Plasma Mass Spectrometry with HNO<sub>3</sub>-HF

As strategic national mineral resources, rare earth elements are prioritized in the national soil background survey program. Consequently, the development of analytical methods enabling rapid and accurate determination of rare earth elements in soils and sediments is of critical importance. A method for the determination of rare earth elements in soil and sediments by microwave digestion-inductively coupled plasma mass spectrometry with HNO₃-HF was proposed. The samples were completed decomposed by a mixture acid of 3 mL HNO₃- 2 mL HF in microwave digestion tubes for 0.1000 g of sample. The microwave digestion instrument is programmed to rise temperature (5 min to 120 ℃, keep for 5 min; 5 min to 150 ℃, keep for 5 min; 5 min to 190 ℃, keep for 30 min). The optimization experiment results showed that the best amount of hydrofluoric acid was 2 mL. The removal of HF was required, with Ge、Rh、Re as the mixed internal standard elements, using He collision mode to eliminate the interference of polyatomic ions, the sample solution was directly determined by inductively coupled plasma mass spectrometry which was equipped with HF-resistant injection system. The correlation coefficients of the calibration curves for all 16 rare earth elements were greater than 0.999 7, with detection limits ranging from 0.004 μg/g to 0.04 μg/g. The rare earth elements in the certified reference materials were analyzed in accordance with the established experimental methodology. The measured values fell within the acceptable error range of the certified values, with relative standard deviations (<italic>RSD</italic>, <italic>n</italic>=5) ranging from 0.62% to 4.41%. The logarithmic concentration difference (Δlg<italic>C</italic>) remained consistently below 0.06, confirming the accuracy and reliability of the analytical method.