Determination of δ11B by HR-ICP-MS from mass limited samples: Application to natural carbonates and water samples

We present an improved method for accurate and precise determination of the boron isotopic composition (B-11/B-10) of carbonate and water samples using a mineral acid matrix and HR-ICP-MS. Our method for delta B-11 determination utilizes a micro-distillation based boron purification technique for both carbonate and seawater matrices. The micro-distillation method is characterized by low blank (<= 0.01 ng-B) and 99.8 +/- 5.7% boron recovery. We also report a new ICP-MS method, performed in a hydrofluoric acid matrix, using a jet interface fitted Thermo (R) Element XR that consumes <3.0 ng-B per quintuplicate analyses (+/- 0.5 parts per thousand, 2 sigma, n = 5). A comparatively high matrix tolerance limit of <= 50 ppb Na/K/Mg/Ca characterizes our ICP-MS method. With an extremely low procedural blank (<= 0.05 +/- 0.01 ng-B) the present isotope method is optimized for rapid (similar to 25 samples per session) analysis of small masses of carbonates (foraminifera, corals) with low boron abundance and small volume water samples (seawater, porewater, river water). Our delta B-11 estimates of seawater (39.8 +/- 0.5 parts per thousand, 2 sigma, n = 30); SRM AE-120 (-20.2 +/- 0.5 parts per thousand, 2s, n = 33); SRM AE-121 (19.8 +/- 0.4 parts per thousand, 2s, n = 16); SRM AE-122 (39.6 +/- 0.5 parts per thousand, 2s, n = 16) are within analytical uncertainty of published values. We apply this new method to assess the impacts of laboratory handling induced sample contamination and seawater physio-chemical parameters (temperature, pH, and salinity) on marine carbonate bound delta B-11 by analyzing core-top planktonic foraminifera samples. (C) 2014 Elsevier Ltd. All rights reserved.