x62 TIMS 87SR/86SR RESULTS for NIST 987.
We measure high-precision Sr isotopes on single Re filaments with a Ta-oxide activator. Measurements are made in three-sequence dynamic mode, typically with several volts on 88Sr. Data are corrected for instrumental bias with an exponential law relative to 86Sr/88Sr = 0.1194 . Small corrections are also made for 87Rb on 87Sr by measuring 85Rb. Long-term results for NIST 987 are well within of the accepted value. For small Sr samples, we utilize 10^12 ohm resistors, with little sacrifice in precision.
We also offer Sr-isotopic analyses with the Neptune MC-ICP-MS. Sample throughput is significantly greater, but precision is generally limited due to the presence of trace amounts of Kr in Ar (plasma) gas that interferes with 86Sr. Consequently, Sr-isotope analyses MC-ICP-MS are suitable only for larger Sr samples where Kr interference is minimized.