Boron isotopic analysis of natural fresh and saline waters by negative thermal ionization mass spectrometry

Negative thermal ionization mass spectrometry (NTIMS) is an effective and robust analytical method which allows to analyze the boron isotopic composition (δ11B) of natural waters directly with an analytical uncertainty of ± 0.5‰ (2σm, corresponding to 2σ/n0.5, where n = 3 − 8 replicate analyses), determined by analysis of a large number (N = 70) of natural fresh and saline waters. A similar reproducibility has been determined for the NIST SRM-951 standard (11B/10B = 4.00125 ± 0.00264 (2σm), n = 5). It is shown that B concentrations of aqueous samples can be increased by a simple dry down procedure (T = 45–50°C) to allow even low-mineralized waters (B ≤ 0.1mg/1) to be analyzed directly, without separation of boron prior to NTIMS isotope dilution analysis.