Auro Maureen E. author Robinson Laura F. author Burke Andrea author Bradtmiller Louisa I. author Fleisher Martin Q. author Columbia University. Lamont-Doherty Earth Observatory Anderson Robert F. author Columbia University. Lamont-Doherty Earth Observatory Columbia University. Earth and Environmental Sciences Columbia University. Lamont-Doherty Earth Observatory originator text Articles 2012 English The GEOTRACES program requires the analysis of large numbers of seawater samples for 232Th, 230Th, and 231Pa. During the GEOTRACES international intercalibration exercise, we encountered unexpected difficulties with recovery and contamination of these isotopes, 232Th in particular. Experiments were carried out to identify the source of these issues, leading to a more streamlined and efficient procedure. The two particular problems that we identified and corrected were (1) frits in columns supplied by Bio-Rad Laboratories caused loss of Th during column chemistry and (2) new batches of AG1-X8 resin supplied by Bio-Rad Laboratories released more than 100 pg of 232Th during elution of sample. To improve yields and blanks, we implemented a series of changes including switching to Eichrom anion exchange resin (100-200 μm mesh) and Environmental Express columns. All Th and Pa samples were analyzed on a Neptune multi-collector inductively-coupled-plasma mass spectrometer (MC-ICP-MS) using peak hopping of 230Th and 229Th on the central SEM, with either 232Th, 236U (or both) used to monitor for beam intensity. We used in-house laboratory standards to check for machine reproducibility, and the GEOTRACES intercalibration standard to check for accuracy. Over a 1-y period, the 2 s.d. reproducibility on the GEOTRACES SW STD 2010-1 was 2.5% for 230Th, 1.8% for 232Th, and 4% for 231Pa. The lessons learned during this intercalibration process will be of value to those analyzing U-Th-Pa and rare earth elements as part of the GEOTRACES program as well as those using U-series elements in other applications that require high yields and low blanks, such as geochronology. Chemical oceanography 10 464 474 2012 http://dx.doi.org/10.4319/lom.2012.10.464 http://hdl.handle.net/10022/AC:P:14509 NNC NNC 2012-08-27 15:38:48 -0400 2012-08-27 15:46:18 -0400 8529 eng