Trace analysis of single zircons for rare-earth elements, U and Th by electrothermal vaporisation-inductively coupled plasma-mass spectrometry (ETV-ICP-MS)

A method is described for the trace analysis of single zircons for Y, La, Ce, Nd, Sm, Yb, Th and U by electrothermal vaporisation-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). Zircons are cleaned by an abrasion process and dissolved in HNO3 and HF in a pressure vessel. Following conversion to chlorides and evaporation to dryness, the dissolved zircon residue is re-dissolved in 500 μl of high-purity 2.5 M HNO3. Analyte concentrations were measured with a precision of ∼ ±6%. Agreement between found and reference values for BCS-388 zircon reference material was excellent. Limits of detection for the analysis of a 10-μg zircon were 150 ng g−1 for Y, 90 ng g−1 for La, 115 ng g−1 for Ce, 65 ng g−1 for Nd,180 ng g−1 for Sm, 22 ng g−1 for Yb, 190 ng g−1 for Th and 80 ng g−1 for U. Absolute limits of detection for a 10-μl solution aliquot ranged from 4 to 36 fg (10−15 g). Zircon solutions were analysed using external calibration by aqueous standards with the addition of a mixed component carrier (NASS-3 open ocean seawater). No matrix or spectroscopic interferences were observed from major-element matrix components. The analysis of a typical set of single zircons gave concentration levels well above the limit of detection for all elements except La.