Laboratory Standards and Blanks

Reproducibility of 87Sr/86Sr in BCR-2 (basalt), JB-2 (basalt), and JLs (limestone)

143Nd/144Nd for BCR-2

Neodymium analyses are normalized to JNdi-1 using 143Nd/144Nd = 0.512115 (Tanaka et al., 2000)

Graph showing BCR-2 (Basalt) data with red data points and error bars, horizontal lines at average values in blue and red for comparison, and text annotations with statistical details.
Graph titled JB-2 (Basalt) showing measurements of 87Sr/86Sr ratios with data points, error bars, and average values, from UCSB TIMS and GeoReM studies.
Graph titled 'JLs-1 (Limestone)' showing measurement values with red and blue lines, error bars, and average statistics in red and blue text.

Strontium analyses are normalized to SRM 987 using 87Sr/86Sr = 0.710240

Reproducibility of 143Nd/144Nd in BCR-2

Lead Isotopes

NIST SRM 981 (NBS 981) is a lead (Pb) isotopic standards (along with NBS 982 and NBS 983) developed by the National Bureau of Standards to span the range of Pb isotope compositions found in nature. NBS 981 is the most-widely used standard for lead isotope analysis. A lead isotope analysis cannot be corrected for mass fractionation using internal normalization (unlike Sr and Nd). Therefore, measurements are made using a 207Pb-204Pb double-spike (DS) which enables mass fractionation correction. Replicate analyses of NBS981 by DS-TIMS over a 10 month period yields reproducibility of 124 ppm (2 SD), 142 ppm (2 SD), and 182 ppm (2 SD) for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, respectively.

Graph showing double-spike 207Pb/204Pb measurements of NBS 981 over time

Unfortunately, several studies (Baker et al., 2004; Weis et al., 2006; Jweda et al., 2016) have demonstrated that Pb isotopes in BCR-2 are highly variable which is possibly related to Pb contamination during preparation of this standard by the USGS. The JB-2 basalt certified reference material (CRM) developed by the Geological Survey of Japan shows much better reproducibility of Pb isotopes compared to USGS rock standards. Nine analysis of JB-2 (basalt)—from 9 different aliquots of powder dissolved and run through column chemistry separately—in the same turret yielded reproducibility of 164 ppm (2 SD), 129 ppm (2 SD), and 131 ppm (2 SD) on 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively.

Graph titled JB-2 (Basalt) showing measurements of 207Pb/204Pb over 204Pb with red data points and error bars. The table at the top indicates an average of 15.5574 with a ± 0.0014 standard deviation, from UCSB DS-TIMS with 9 samples. The bottom blue label shows an average of 15.5582 with a ± 0.0016 standard deviation, from Baker et al., 2004.
Graph showing double-spike 206Pb/204Pb measurements of NBS 981 over time
Graph showing double-spike 208Pb/204Pb measurements of NBS 981 over time
Line graph titled JB-2 (Basalt) showing measurements of 206Pb/204Pb over multiple data points, with two average lines and error bars for each data point. The red text indicates an average of 18.3420 with a standard deviation of 0.0025 based on 9 samples. The blue text shows an average of 18.3423 with a standard deviation of 0.0017 based on Baker et al., 2004.
Scientific graph comparing measurements of JB-2 basalt sample. The graph shows individual data points with error bars, mean value, and two reference lines Iabeled with average values from two different studies. The Y-axis measures ratios of lead isotopes, and the title indicates the sample type.

Laboratory Blanks

Full-chemistry blanks — sample dissolution, chemical separation, and filament loading — for basalt samples (~100-200mg) are typically < 50pg for Sr, <15 pg for Nd, and <20pg for Pb. For ultra-low level analyses (i.e. single mineral grain or melt inclusion) blanks are typically <10pg for Sr and <2pg for Nd.