METHOD OPTIMIZATIONS OF IRON (III) MAGNESIUM HYDROXIDES CO-PRECIPITATION FOR ANALYSIS OF RARE EARTH ELEMENTS IN SOILS
Abstract
Rare earth elements (REEs) were proved to increase growth, development as well as yield and quality of crops. REEs were often added to fertilizers in trace forms and fairly high contents in the Earth's crust. However, a complex matrix of soils, and the presence of elements such as aluminum, and iron could affect the accuracy in the direct determination of REEs in original sample matrix using ICP – MS. This study aimed to optimize the sample preparation using co-precipitation of Fe(OH)3 and Mg(OH)2 to exclude the sample matrix prior to analyzing the content of REEs on ICP – MS. The results showed that concentrations of Fe3+:Mg2+ = 500:500 (mg L-1), TEA = 3% and NaOH = 30% (i.e., adjusting pH ~ 14) were optimal conditions of REEs co-precipitation. Recoveries of REEs were greater than 90%. Method detection and quantitation limit (MDL and MQL) of REEs ranged from 0.019 to 0.24 mg kg-1 and 0.06 to 0.80 mg kg-1, respectively. Applying the optimized method for soil samples, the content of REEs was in the ranges of 0.022 mg kg-1 and 46.0 mg kg-1.