Improving boron isotope ratio measurement precision with quadrupole inductively coupled plasma-mass spectrometry

A method was developed to improve the precision of inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for the determination of boron isotope ratios (¹¹B/¹⁰B) in various environmental materials including seawater. This approach is based on the common analyte internal standardization (CAIS) chemometric algorithm. The sample solution obtained after digestion is spiked with lithium, and both ⁷Li/⁶Li and ¹¹B/¹⁰B values are measured using long-counting periods (20 min). The CAIS algorithm corrects the measured ¹¹B/¹⁰B values for (a) statistical fluctuations resulting from short-term noise; (b) drift in ¹¹B-to-¹⁰B ratio as a result of long-term deviation in instrumental parameters likely to occur during long counting times; (c) change in ¹¹B-to-¹⁰B ratio caused by variation in matrix elements concentrations; and (d) drift in mass bias correction factor. Comparing boron isotopic ratios in seawater measured by conventional and the new isotope ratio methods validates the procedure. A synthetic isotopic mixture of boron SRM 951 and enriched ¹⁰B SRM 952 also was examined. The CAIS method provided a measured boron isotopic ratio precision of 0.05% R.S.D. while eliminating 5.1% matrix concentration error and 0.25% instrumental drift error.