A technique of the microwave digestion of mafic and ultramafic rocks is developed for ICP-MS determination of the rare earth elements. A series of experiments was carried out to optimize the digestion parameters (temperature, acid ratio, sample mass) in a microwave system MARS-5. A mixture of acids HF and HNO3 in a volume ratio of 4:1 was used at the first stage (60 min, 190°C, maximum pressure 20 atm), and after distilling off the excess fluorides in the form of SiF4 the dry residue was treated with aqua regia (60 min, 190°C, maximum pressure 20 atm). Measurements were carried out using a double-focusing ICP mass spectrometer ELEMENT Finnigan Mat. Multielement standard solution with an acidic composition similar to the analyzed solutions was used for external calibration and indium was used as an internal standard. The detection limits were 0.0002 – 0.008 μg/g. The digestion technique was validated by analysis of the geological reference materials BHVO-2 and BCR-2 (basalts), UB-N (serpentinite), JP-1 (peridotite). The relative standard deviations for the determined elements were below 8% for reference materials BHVO-2, BCR-2, and UB-N, and ranged within 10 – 35% for JP-1 sample. The developed technique was used for determination of the rare earth elements in Kola Peninsula rocks. The correctness of the results was confirmed by comparison with the results of ICP-MS analysis after fusion with lithium metaborate. The rapidity compared to acid decomposition without using a microwave system and low detection limits compared to fusion are the apparent advantages of the developed technique.
Determination of Rare-Earth Elements in a Limestone Geological Standard Reference Material by ICP-MS Following Solvent Extraction.