Precise isotope ratio measurement by multicollector-ICP-MS without matrix separation

The methods reported here employ multiple collector inductively coupled plasma mass spectrometry to produce high precision measurements of Sr, Pb, U and Cu isotope ratios in various samples, using internal standards, without matrix separation. Strontium isotope ratios were determined in natural waters, carbonates and related materials. The precision (2σ) of the ⁸⁷Sr/⁸⁶Sr ratio was 0.002% (20ppm), even in samples with total dissolved solids (TDS) levels of up to 500 mg/L. Isotope ratios of Pb were measured in NIST SRM 610 glass and on natural water sources spiked with NIST SRM Pb 981. Lead and U isotope ratios were measured on Mn-nodules from Timna Valley of southern Israel. In Pb measurements, the values for the ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios have been determined with precisions of 30 and 40 ppm and those of ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb to ²⁰⁴Pb - with precisions of 130, 170 and 200 ppm, respectively, even with TDS levels of up to 700 mg/L. Measurements of ²³⁴U/²³⁸U ratios were performed with a precision of better than 0.3%. The use of external spiking of a different element as internal standard in Cu isotope ratio measurements was evaluated in order to avoid the tedious "sample-standard bracketing" technique. Experiments were done with both ⁶⁶Zn/⁶⁸Zn and ⁶¹Ni/⁶²Ni ratios as internal standards. The use of Zn was unsuccessful, while Ni improved the precision of the measurements up to 0.03%, particularly by correcting the drift of the isotope ratio,.