Comparison of microsublimation and ion exchange chromatography for boron isolation preceding its isotopic analysis via multi-collector ICP-MS

Abstract

Boron isotopic analysis is of interest in many research fields and for a large variety of sample types. Accurate and precise determination of boron isotope ratios using multi-collector ICP-mass spectrometry or thermal ionization mass spectrometry requires isolation of the target element prior to isotopic analysis, which is accomplished using either ion exchange chromatography or microsublimation. This study systematically compares the two methods in terms of B recovery, procedural blank, matrix removal efficiency, accuracy and precision of the resulting δ¹¹B values as measured using multi-collector ICP-mass spectrometry, as well as labor intensiveness and costs. For this purpose, four types of sample matrices, i.e. 20 g L⁻¹ Ca aqueous solution, seawater, digests of spinach (100 g L⁻¹) and silicate glass (10 g L⁻¹), were stripped from their original B content and spiked with B of known isotopic composition and were then subjected to both sample preparation methods and subsequent isotopic analysis of the purified B fraction via multi-collector ICP-mass spectrometry. For both methods, the highest (quantitative) B recoveries were obtained for Ca-rich aqueous solution and seawater. For spinach, accurate δ¹¹B values were obtained after ion exchange chromatography. However, microsublimation was plagued by isotope fractionation, resulting in large offsets (∼8‰) between the experimental results and the corresponding reference values. For glass, B recovery was incomplete, nevertheless the absence of fractionation rendered both sample preparation methods suitable. Overall, in the absence of isotope fractionation, microsublimation appears advantageous in terms of procedural blanks, matrix removal efficiency, precision (2 s) on δ¹¹B values, labor intensiveness and costs.