The preparation and use of synthetic isotope mixtures for testing the accuracy of the PTIMS method for 10B/11B isotope ratio determination using boron mannitol complex and NaCl for the formation of Na2BO2+

Abstract

The development of a method for determination of isotopic composition requires calibration of the method over a wide range of isotopic ratios. Further, validation of data obtained by the method requires isotopic reference materials spanning a wide range of ratios. In the present studies, gravimetric synthetic mixtures of boron with 10% ¹⁰B to 95% ¹⁰B were prepared by mixing solutions of enriched boron isotopes. The solutions of ¹⁰B and ¹¹B enriched isotopes were calibrated using isotopic reference material NIST SRM-951 as a spike for isotope dilution. ¹⁰B/¹¹B atom ratios in all the blends were determined by Positive Thermal Ionization Mass Spectrometry (PTIMS) using NaCl with mannitol for the formation of Na₂BO₂⁺. A measurement precision of about 0.03% was obtained from repetitive P-TIMS analyses of the mixtures with ¹⁰B content ranging from 10 to 70%. An instrument isotope fractionation factor (K-factor) of 0.99935 ± 0.00030 (1 s) was obtained for ¹⁰B/¹¹B atom ratios of the different blends and this agreed with the K-factor determined from P-TIMS analysis of NIST SRM-951. The different isotopic blends prepared were also used in Inductively Coupled Plasma Quadrupole Mass Spectrometry, (ICP-QMS) employing NIST SRM-951 (¹⁰B/¹¹B ratio of 0.2473) as a bracketing standard. An accuracy and precision of about 0.5% was obtained during ICP-QMS analyses of these mixtures. A novel and simple method for validation of analysis methodology with synthetic mixtures prepared using enriched isotopes is described in the present work.