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.