Analytical Procedures

Sr-Nd-Pb-U-Th-Hf Isotope Procedures

Leaching Procedures

Where required, samples may be washed or leached prior to dissolution, if they are being analysed for isotopic composition only.  Please contact us if you are uncertain as to what procedures may be required for / were carried out on your samples.

Silicate Sample Dissolution

Between 100 and 250 milligrams of powder (occasionally more for low-concentration samples) are dissolved in 50% HF-12N HNO₃, then attacked with 8N HNO₃ and finally 6N HCl.  The residue is taken up in 1N HBr for Pb/Sr/Nd, or 2.5N HCl for Sr/Nd only.

Carbonate Sample Dissolution

Calcites are washed in nanopure water prior to being leached in 5% acetic acid in an ultrasonic bath. Dolomites are washed in nanopure water and dissolved in 6N HCl. The residues are taken up in 7N HNO₃ for Sr-spec columns.

Sulphide Sample Dissolution

Sulphides are dissolved in 7N HNO₃ on a hotplate overnight. Galenas are normally dissolved in 7N HNO₃ at room temperature.

U/Th/Pb

Pb is separated in Bio-Rad 10-ml polyethylene columns and Dowex AG1-8X anion resin, using 1N HBr to elute other elements and 6N HCl to elute Pb. The collected HBr solution is dried, the residue attacked with 8N HNO₃ to eliminate Br, dried again, and the residue is taken up in 8N HNO₃ for U/Th.  The collected Pb solution is dried, redissolved in 1N HBr, and the above procedure is repeated with a small volume resin bed.  U and Th are separated together using the same columns and resin:  other elements are eluted with 7N HNO₃, and U and Th are eluted with ultrapure H₂O.  The HNO₃ solution is dried down and the residue taken up in 2.5N HCl for Sr/Nd.  The U/Th solution is dried, redissolved in HNO₃, and the above procedure is repeated with a small resin bed. Currently, U and Th isotope dilution concentration measurements are not available in our lab because of lack of isotopic spikes for these two elements.

Total procedural blanks for Pb are < 50 picograms.  We use a ²⁰⁸Pb spike (J. Blenkinsop, Carleton University) for Pb concentrations only, and a ²³³U spike (from GEOTOP, Montreal).  Concentrations are precise to + 0.5%.  Samples are loaded onto single Re filaments with H₃PO₄ and silica gel, and are run at filament temperatures of 1250-1350^oC, depending on the gel-type used. 

Analysis of USGS Standard BCR-1 yields Pb = 13.56 ppm, U = 1.70 ppm, Th = 5.86 ppm, ²⁰⁶Pb/²⁰⁴Pb = 18.818, ²⁰⁷Pb/²⁰⁴Pb = 15.633, and ²⁰⁸Pb/²⁰⁴Pb = 38.633 (average of 2 runs, see Tatsumoto et al.)  All mass spectrometer runs are corrected for fractionation using NIST SRM981. 

The average ratios measured for SRM981 are:

Triton: ²⁰⁶Pb/²⁰⁴Pb = 16.899± 0.012, ²⁰⁷Pb/²⁰⁴Pb = 15.439± 0.016, and ²⁰⁸Pb/²⁰⁴Pb = 36.537 ± 0.05 (2 s.d.), based on 64 runs between January 2016 – March 2018. Our subsequent fractionation correction is based on the values of Todt et al. (1984).

Neptune: ²⁰⁶Pb/²⁰⁴Pb=16.9312± 0.0013, ²⁰⁷Pb/²⁰⁴Pb =15.4848± 0.0017, and ²⁰⁸Pb/²⁰⁴Pb = 36.676 ± 0.007 (2 s.d.), based on 52 runs between January and February 2020. Pb sample solutions are doped with Tl solution (in a mass ratio of Tl/Pb =1:4) so that the Pb isotope ratios can be normalized to ²⁰³Tl/²⁰⁵Tl=0.418922 to correct for the mass fractionation. A further normalization based on the values of Todt et al. (1984) is also applied.

Rb/Sr

Each silicate sample, dissolved in 2.5N HCl, is pipetted into a 14-ml Bio-Rad borosilicate glass chromatography column containing 3.0 ml of Dowex AG50W-X8 cation resin.  Rb and Sr are eluted in succession using 2.5 N HCl.  If required, the rare earth elements are then eluted using 6N HCl.  The REE solution is dried and the residue dissolved in 0.26N HCl.

Carbonate and water samples are loaded in 7N HNO₃ onto small (5cm x 5mm i.d.) polypropylene columns containing Eichrom Sr-spec resin, and Sr is eluted in water.

Total procedural blanks for Sr are < 250 picograms.  We have two mixed ⁸⁷Rb/⁸⁴Sr spikes, one for felsic rocks and another for mafic to intermediate rocks.  Sr is loaded onto a single Ta filament with H₃PO₄ and is run at filament temperatures of 1350-1500^oC. Sr is also measured on Neptune MC-ICPMS in 2%HNO3 with a concentration ranging from 100 ppm to 150 ppb. Isotope ratios are normalized to ⁸⁶Sr/⁸⁸Sr = 0.11940 to correct for fractionation.  Two standards are run at Carleton, NIST SRM987 (Triton: ⁸⁷Sr/⁸⁶Sr = 0.710239 ±19, n=60, since June 2018; Neptune: ⁸⁷Sr/⁸⁶Sr = 0.710245 ±26, n=55, since March 2019) and the Eimer and Amend (E&A) SrCO₃ (Triton: ⁸⁷Sr/⁸⁶Sr = 0.708013 ±15, n=12, August 2010 – June 2014). Results for USGS BCR-2 and BHVO-2 during a period from June 2018 to March 2020 are as follows, Triton: BCR-2, ⁸⁷Sr/⁸⁶Sr = 0.705001 ±20, n=8, BHVO-2, ⁸⁷Sr/⁸⁶Sr = 0.703475, n=2; Neptune: BCR-2, ⁸⁷Sr/⁸⁶Sr = 0.705003 ±22, n=14, BHVO-2, ⁸⁷Sr/⁸⁶Sr = 0.703485, n=2. Rb is loaded with H₃PO₄ onto one side of a double Re filament assembly and run at temperatures of 1250-1300 ^oC.  No correction for fractionation is made.

Sm/Nd

REE fractions are dissolved in 0.26N HCl and loaded onto Eichrom Ln Resin chromatographic columns containing Teflon powder coated with HDEHP [di(2-ethylhexyl) orthophosphoric acid, Richard et al., 1976]. Nd is eluted using 0.26N HCl, followed by Sm in 0.5N HCl. 

Total procedural blanks for Nd are < 50 picograms; < 6 picograms for Sm.  Samples > 250Ma are spiked with a mixed ¹⁴⁸Nd-¹⁴⁹Sm spike prior to dissolution.  Concentrations are precise to ± 1%, while ¹⁴⁷Sm/¹⁴⁴Nd ratios are reproducible to 0.5%.  Samples are loaded with H₃PO₄ on one side of a Re double filament, and run at temperatures of 1700-1800 ^oC. Nd can also be measured on Neptune MC-ICPMS in 2%HNO3 with a concentration ranging from 100 to 200 ppb. Isotope ratios are normalized to ¹⁴⁶Nd/¹⁴⁴Nd = 0.72190.  Analyses of the USGS standards on Triton yield, BCR-1: Nd = 29.02 ppm, Sm = 6.68 ppm, and ¹⁴³Nd/¹⁴⁴Nd = 0.512668 +/- 20 (n=4); BCR-2: Nd = 28.39 ppm, Sm = 6.556 ppm (n=3), and ¹⁴³Nd/¹⁴⁴Nd = 0.512623 ±12 (n=7, June 2018-March 2019), BHVO-2: ¹⁴³Nd/¹⁴⁴Nd = 0.512963 (n=1). Analyses of the USGS standards on Neptune yield, BCR-2: Nd = 28.35 ppm, Sm = 6.530 ppm (n=1), and ¹⁴³Nd/¹⁴⁴Nd = 0.512626 ±6 (n=8, February-December 2019), BHVO-2: Nd = 24.13 ppm, Sm = 6.031 ppm (n=2), ¹⁴³Nd/¹⁴⁴Nd = 0.512973 ±15 (n=4). The international La Jolla standard produces: TRITON: ¹⁴³Nd/¹⁴⁴Nd = 0.511847±7, n = 26 (Feb 2005 – June 2007).  The international JNdi-1(Tanaka et al, 2000) standard produces: Triton, ¹⁴³Nd/¹⁴⁴Nd = 0.512095, n = 2 (October-November 2019); Neptune, ¹⁴³Nd/¹⁴⁴Nd = 0.512085± 9, n= 34 (April 2019 – March 2020). Internal lab Nd standard ¹⁴³Nd/¹⁴⁴Nd = 0.511818 ± 8, n = 28 (Feb 2005-June 2007); 0.511819 ± 10, n = 94 (Feb 2005 – Aug 2009); 0.511823 ± 12, n = 65 (October 2010 – July 2012); 0.511830 ±12, n = 170 (August 2012 – March 2018); 0.511814 ± 9, n = 23 (June 2018 – November 2019).

Lu/Hf

The dried sample residues are dissolved in 2ml of 3M HCl and loaded onto a pre-packed 2ml Ln-resin columns (Eichrom Technologies); the columns are then washed in 15 ml of 3MHCl and the eluents are collected for subsequent Sr, Sm and Nd separation; Lu and Hf are then eluted following a procedure described in Yang et al’s (2010). Hf is measured on Neptune in 2%HNO3 with trace HF. Hf isotopic ratios are normalized against ¹⁷⁹Hf/¹⁷⁷Hf=0.7325. The results of IGGRC Neptune MC-ICPMS routine measurements of bracketing standard reference materials during a period of twelve months are: JMC475 ¹⁷⁶Hf/¹⁷⁷Hf= 0.282169±0.000011 (2SD, n=32), BCR-2 ¹⁷⁶Hf/¹⁷⁷Hf=0.282867±0.000015 (n=4) and BHVO-2 ¹⁷⁶Hf/¹⁷⁷Hf=0.283115 (n=1). The total procedure blanks are <70pg.

References:

Richard, P., N. Shimizu, and C. J. Allègre, 143Nd/146Nd, a natural tracer: an application to oceanic basalts, Earth Planet. Sci. Lett., 31, 269-278, 1976.

Tatsumoto, M., R. J. Knight, and M. H. Delevaux, Uranium, thorium, and lead concentrations in three silicate standards and a method of lead isotopic analysis, U.S.G.S. Prof. Paper 800-D, , D111-D115, 1972.

Todt, W., R. A. Cliff, A. Hanser, and A. W. Hofmann, 202Pb -205Pb spike for Pb isotopic analysis, Terra Cognita, 4, 209, 1984.

T.Tanaka, S.Togashi, H.Kamioka,H. Amakawa, H. Kagami, T. Hamamoto, M.Yuhara,Y.Orihashi, S.Yoneda, H.Shimizu,T.Kunimaru, K.Takahashi, T.Yanagi, T.Nakano,H.Fujimaki, R.Shinjo, Y.Asahara, M.Tanimizu, C.Dragusanu 2000, JNdi-1: a neodymium isotopic reference in consistency with LaJolla neodymium, Chem. Geol. 168, 279-281.

 Y. Yang, H. Zhang, Z. Chu, L. Xie, F. Wu 2010, Combined chemical separation of Lu, Hf, Rb, Sr, Sm and Nd from a single rock digest and precise and accurate isotope determinations of Lu–Hf, Rb–Sr and Sm–Nd isotope systems using Multi-Collector ICP-MS and TIMS, International Journal of Mass Spectrometry, 290, 120-126.