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

A method was developed to improve the precision of inductively coupled plas ma quadrupole mass spectrometry (ICP-QMS) for the determination of boron is otope ratios (B-11/B-10) in various environmental materials including seawa ter. 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 Li-7/Li-6 and B-11/B-10 values are measure d using long-counting periods (20 min). The CAIS algorithm corrects the mea sured B-11/B-10 values for (a) statistical fluctuations resulting from shor t-term noise; (b) drift in B-11-to-B-10 ratio as a result of long-term devi ation in instrumental parameters likely to occur during long counting times ; (c) change in B-11-to-B-10 ratio caused by variation in matrix elements c oncentrations; and (d) drift in mass bias correction factor. Comparing boro n isotopic ratios in seawater measured by conventional and the new isotope ratio methods validates the procedure. A synthetic isotopic mixture of boro n SRM 951 and enriched B-10 SRM 952 also was examined. The CAIS method prov ided a measured boron isotopic ratio precision of 0.05% R.S.D. while elimin ating 5.1% matrix concentration error and 0.25% instrumental drift error. ( C) 2000 Elsevier Science B.V. All rights reserved.