Rapid Decomposition Of Geological Samples By Ammonium Bifluoride (Nh4hf2) For Combined Hf-Nd-Sr Isotope Analyses

Rationale Complete decomposition of silicate rock matrices is crucial in determining their isotopic compositions, but acid dissolution in a high-pressure steel-jacketed bomb, which has been the only powerful, effective technique thus far, is time-consuming and expensive. Rock dissolution using ammonium bifluoride (ABF), as described here, is a viable alternative.Methods Geological reference materials (GRMs) were digested using ABF in closed Teflon beakers at temperatures of 220/230 degrees C in a convection oven and subsequently treated with HNO3. Hf-Sr-Nd were separated and purified using ion-exchange chemistry columns calibrated for 50-2 mg samples. The isotopic compositions of Sr-Nd were measured by Thermal Ionization Mass Spectrometry, while that of Hf by Multi-Collector Inductively Coupled Plasma Mass Spectrometry, both with normal 10(11) omega and gain calibrated 10(13) omega amplifiers.Results Total procedural blanks of our protocol are 0.5 ng for Sr, 0.2 ng for Nd and <25 pg for Hf. Test runs with GRMs, ranging in composition from basic to felsic and dissolved in ABF, yield accurate Sr-87/Sr-86, Nd-143/Nd-144 and Hf-176/Hf-177 isotope ratios as compared with those obtained with the bomb dissolution technique. Reproducibilities were comparable, on the order of 10-20 ppm. Our technique allows combined Hf-Sr-Nd isotope analyses of low-mass (50-2 mg) samples.Conclusions The ABF digestion is an alternative technique to high-pressure bomb dissolution in matrix decomposition for accurate and reproducible Hf-Nd-Sr isotope analyses of geological samples within a reasonable time (3-4 days), with high sample throughput and low costs in geochemistry and environmental sciences.