87Rb-87Sr

Strontium isotope ratios are measured on single Re filaments with a tantalum oxide emitter solution in a three sequence dynamic routine utilizing five Faraday cups. By maintaining a 4V ⁸⁸Sr beam for 150 cycles, an internal precision of 4 ppm (1-sigma) on the ⁸⁷Sr/⁸⁶Sr ratio is consistently achieved with an exponential law correction relative to ⁸⁶Sr/⁸⁸Sr = 0.1194. External reproducibility of the NBS-987 Sr standard since installation has been maintained at 0.710251 ± 4 (6 ppm, 1-sigma, n=61; literature value=0.710248).

We are capable of measuring the Sr isotopic compositions of a variety of rocks, minerals, fossil material, waters and soils. We also have carefully calibrated mixed ⁸⁷Rb-⁸⁴Sr spikes suitable for isotope dilution measurements of ⁸⁷Rb/⁸⁶Sr in low-Rb (whole rocks, feldspars, apatite, carbonates) and high-Rb (micas) samples.