Accurate and Precise Determination of Boron Isotopic Ratios at Low Concentration by Positive Thermal Ionization Mass Spectrometry Using Static Multicollection of Cs_2BO_2~+ Ions

摘要

A static double-collector system for accurate, precise, and rapid boron isotope analysis has been established by employing a newly fixed Faraday H3 and H4 cup enabling simultaneously collected Cs_2BO_2~+ ion beams (m/z = 308 and 309) on a Finnigan-MAT Triton thermal ionization mass spectrometer of boron (Triton B). The experimental result indicated that Cs_2BO_2~+ ion beams (m/z = 308 and 309) were simultaneously collected using a fixed Faraday H3 and H4 cup without using the "Zoom Quad" function and reduced accelerating voltage. Furthermore, the method enabled the measurement of samples containing as little as 20 ng of boron. An analysis of the National Institute of Standards and Technology standard reference material (NIST SRM) 951 standard showed external reproducibility (2RSD) of ±0.013‰, ± 0.013‰, and ±0.019‰ for 100, 50, and 20 ng of boron, respectively. The present method of static multicollection of Cs_2BO_2~+ ions is applicable to a wide field of boron isotopic research that requires high precision and accuracy to analyze samples with low boron concentrations, including pore fluids, foraminifera, rivers, rainwater, and other natural samples.