Determination of Rare Earth Elements in Peridotite by Inductively Coupled Plasma-Mass Spectrometry after Alkali Fusion and Mg(OH)₂ and Fe(OH)₃ Coprecipitation

Characteristics of REEs in peridotite is significant for studying petrogenesis and magmatic processes. Due to the serious interference of matrix elements such as Mg and Fe, it is difficult to determine the low contents of REEs in peridotite (∑REEs=0.1-1 μg/g) accurately. The previous method was sealed acid digestion at high pressure combined with ion-exchange which was used to separate REEs and matrix elements of Mg and Fe and preconcentrate REEs. However, due to the long digesting time (almost 7 days) and various operating steps, it is not conducive to the analysis of lots of samples. In this study, the sample was decomposed by Na₂O₂ alkali fusion, and coprecipitated with Mg(OH)₂ and Fe(OH)₃. Then, the solution was separated from precipitation by centrifuging for a rapid separation of REEs from matrix elements of Mg and Fe. Contents of REEs are determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). For this method, the detection limits of REEs range from 0.17 to 2.18 ng/g, and the recoveries are 95%-101%. This method was used to analyze the national standard reference materials GBW07101 and GBW07102. The relative error between analytical results and recommended values is less than 20%, and the relative standard deviation (RSD, n=11) is less than 10%. The method not only reduces the losses caused by stepped precipitation, but also shortens the analysis period (only one day for sample-digestion). It is simple to operate, and efficient in analysis.