Hf and Lu isotopic reference values for the zircon standard 91500 by MC-ICP-MS

The Hf and Lu isotopic ratios of the zircon standard 91500 have been redefined by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The chemical protocol consists of a high-pressure and high-temperature acid dissolution of zircon followed by optimized two-step ion-exchange chromatography with an overall recovery better than 94%. Instrumental calibration involved an extensive characterization of standard solutions for Hf [JMC-475 250 ppb: 176Hf/177Hf=0.282161±16 (2 S.D.)] and Lu [JMC standard 50 ppb: 175Lu/176Lu=37.72±2 (2 S.D.)]. A total of 59 Hf isotopic measurements on the zircon standard 91500, including four independent dissolutions and purifications, were carried out on two Nu Plasma MC-ICP-MS instruments. The average 176Hf/177Hf is 0.282302±8 (2 S.D.) and the two MC-ICP-MS instruments give overlapping results within error. These high precision data [external error: 27 ppm (2 S.D.) for 59 measurements and 10 ppm for a single day; internal error: 10 ppm (2 S.D.)] are reproducible between duplicates and underscore the stability of the analytical protocol. The Lu isotopic composition of the zircon standard 91500 has also been redefined: 175Lu/176Lu=37.74±8 (2 S.D.). With the growing use of in situ measurement techniques using MC-ICP-MS technology, such precise reference values will be important for the calibration of laser ablation analyses in the future.