Lithium Isotopic Ratios by Single‐Collector ICP‐SFMS: A Critical Evaluation Using Reference Materials

Abstract

We deployed a procedure to measure Li isotope ratios on a single‐collector sector field inductively coupled plasma mass spectrometer (ICP‐SFMS) operated with a desolvation system and a high‐sensitivity skimmer cone. Under optimised instrumental acquisition conditions, chromatographically separated analyte solutions containing 1 ng g−1 of Li provided adequate sensitivity using analogue mode detection for both isotopes, without adverse memory effect. Unprecedented for this isotopic system, we estimated the expanded uncertainty (U; k = 2) associated with the obtained δ7Li values to validate the procedure. Were considered as potential contributors to the combined uncertainty estimation (uc) the measurement intermediate precision, sample digestion and homogeneity, chromatographic separation, procedural blanks and homogeneity of the bracketing measurement standard (IRMM‐016). The estimated U was on average (from results obtained with reference materials) 1.2‰ (k = 2). This is about twice the intermediate measurement precision (2s) of our data, highlighting the importance of evaluating other measurement uncertainty sources. The δ7Li values obtained for nineteen silicate rocks and one natural water agree with published values. We also provide the first δ7Li = (1.7 ± 1.2; 0.7)‰ (mean value ± U (k = 2); intermediate precision (2s); n = 13) for basalt RM BRP‐1.