Separation of high field strength elements (Nb, Ta, Zr, Hf) and Lu from rock samples for MC‐ICPMS measurements

Abstract

[1] Abstract: The application of multiple collector inductively coupled plasma source mass spectrometry (MC-ICPMS) to 176 Hf and 92 Zr chronometry has been hampered by complex Zr-Hf purification procedures that involve multiple ion exchange column steps. This study presents a single-column separation procedure for purification of Hf and Lu by ion exchange using Eichrom 1 LnSpec resin. The sample is loaded in pure HCl, and element yields are not dependent on the sample matrix. For 92 Zr chronometry, a one-column procedure for purification of Zr using Biorad 1 AG-1-Â 8 resin is described. Titanium and Mo are completely removed from the Zr, thus enabling accurate 92 Zr measurements. Zirconium and Nb are quantitatively separated from rock samples using Eichrom Ln-Spec resin, allowing measurements of Zr/Nb with a precision of better than ±5% (2s). The Ln-Spec and anion resin procedures may be combined into a three-column method for separation of Zr-Nb, Hf, Ta, and Lu from rock samples. For the first time, this procedure permits combined isotope dilution measurements of Nb/Ta, Zr/Hf, and Lu/Hf using a mixed 94 Zr-176 Lu-180 Hf-180 Ta tracer. Analytical protocols for Zr and Hf isotope measurements using the Micromass Isoprobe, a second generation, single-focusing MC-ICPMS, are reported. Using the Isoprobe at Münster, 2s external precisions of ±0.5e units for Hf and Zr isotope measurements are achieved using as little as 5 ng (Hf ) to 10 ng (Zr) of the element. The 176 Hf/ 177 Hf and Lu/Hf for rock reference materials agree well with other published MC-ICPMS and thermal ionization mass spectrometry (TIMS) data.

Improved method for Hf separation from silicate rocks for isotopic analysis using Ln-spec resin column

“…The chemical separation technique described herein (Table 1) is a two -step procedure based on the modification of previously described techniques using Ln -spec resins from Eichrom Technologies (USA) (Münker et al, 2001).…”

“…Ascorbic acid was added to reduce the concentration of Fe 3+ ions, which are known to strongly adsorb onto the Ln -spec resin (Münker et al, 2001).…”

“…Consequently, the column size and acids used in the separation procedures increase in scale, and the procedures require a large amount of time. Münker et al (2001) proposed a simple method for Hf separation (involving a single -column path) from a 0.1 -g silicate rock sample; however, this method requires a prohibitively large volume of washing acids (600 ml) before elution of Hf for a larger sample size of 0.5 g. As a result of all these factors, Hf isotope measurement using the TIMS is quite challenging; this hinders TIMS users from carrying out efficient analyses. Hence, a simpler, more efficient separation procedure than the ones currently available would be a very helpful and preferable improvement for existing and prospective TIMS users.…”

“…Our proposed method uses Ln -spec resin, and it is a modification of Münker et al (2001). The procedure proposed in this study is rapid and simple, and it enables efficient removal of other high field strength elements (HFSE) such as Ti, Zr, Nb and Ta, and HREE (Yb, Lu).…”

“…Several separation procedures and digestion methods have been proposed for Hf separation. Recent separation methods exploit the properties of specialized extraction chromatographic resins designed for nuclear industry application (Ln -spec, Münker et al, 2001;TEVA -spec, Le Fèvre and Pin, 2002, Bizzarro et al, 2003TODGA, Connelly et al, 2006; UTEVA -spec, Lu et al, 2007).…”