Determination of trace rare earth elements in plant and soil samples by inductively coupled plasma-mass spectrometry

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was employed to deter mine the concentration of rare earth elements (REEs) in plants and soils. S ample preparation and analytical conditions were investigated to set up a s imple routine procedure for measuring rare earth elements. For prompt sampl e decomposition, a microwave digestion technique was successfully used with an acid mixture of HCl+HNO3+HF Detection limits, reproducibility, accuracy and possible interference were also studied. ICP-MS provided extremely low detection limits for REEs (0.6-6ng/l). Precision was typically better than 6% RSD(relative standard deviation) for soil and 10% for plant. The potent ial of the method was evaluated by analysis of standard reference materials of soils and plants. A good agreement between the experimental results and certified values was observed. The spectroscopic interference of Pa with E u and light REEs(LREEs, La-Eu) with heavy REEs(HREEs, Gd-Lu) were eliminate d by the algebra correction. The results suggested that REEs in soil samples existed mainly as light REE s, and the same concentration distribution patterns of Oddo-Hakins law were observed, showing negative gradient from La to Lu concentrations. The REE contents in plants were very low, less than 20 mu g/g and varied with plant species. Apart from rape leaf(Brassica juncea), the REE distribution patte rns in other plant leaves were consistent with soils, indicating that these plants generally absorbed REEs from soil without selectivity. Rape leaf sh owed selective absorption for LREEs, especially for La. The REE concentrati on distribution in parts of hot pepper(Capsicum annuum) was characteriaed b y root>leaf>stem>fruit. The REEs absorbed by hot pepper concentrated mainly in roots and leaves, very little migrated into fruit. Transfer factors(TFs ) of REEs in plants were very low. Although the contents of LREEs were rela tively more than those of HREEs, no distinct difference of TFs between LREE s and HREEs was observed, meaning that LREEs and HREEs have the same abilit ies of transportation. However, for rape leaf, the TFs of LREEs were one or two orders of magnitude higher than those of HREEs.