ISOTOPE RATIO MEASUREMENT OF LEAD, NEODYMIUM AND NEODYMIUM SAMARIUM MIXTURES, HAFNIUM AND HAFNIUM LUTETIUM MIXTURES WITH A DOUBLE FOCUSING MULTIPLE COLLECTOR INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETER

An inductively coupled plasma (ICP) source coupled to a double focusing magnetic sector mass analyser equipped with seven Faraday detectors has been used to measure the isotopic ratios of lead reference materials using a thallium correction technique. The addition of thallium to the lead standards and the subsequent simultaneous measurement of the thallium and lead isotopes allowed a correction for mass discrimination. Measurement of six samples of National Institute of Standards and Technology (NIST) (formerly National Bureau of Standards) Standard Reference Material Pb-982 revealed Pb-208:Pb-204 = 36.702 +/- 0.022, Pb-207:Pb-204=17.141 +/- 0.009 and Pb-206:Pb-204=36.711 +/- 0.021 compared with the NIST certified values of 36.744 +/- 0.050, 17.159 +/- 0.025 and 36.738 +/- 0.037, respectively. All errors are given as 2sigma. The measurement of each sample used approximately 200 ng of lead and took 100 s. Measurement of six neodymium samples (obtained from Scripps Institute of Oceanography, La Jolla, CA, USA), where internal normalization to Nd-146:Nd-145 is possible, revealed a Nd-143:Nd-144 ratio of 0.511825 +/- 0.000039 compared with the accepted value of 0.511859. Measurement of six La Jolla neodymium samples contaminated with a similar concentration of samarium revealed a Nd-143:Nd-144 ratio of 0.511854 +/- 0.000059. The measurement of each mixed sample used approximately 100 ng of neodymium. Similarly measurement of six samples of Johnson Matthey Company (JMC) 475 Hafnium, normalized to Hf-179:Hf-177, revealed a Hf-176:Hf-177 ratio of 0.282194 +/- 0.000020 compared with the accepted value of 0.282195 +/- 0.000015. Measurement of six samples of JMC 475 Hafnium contaminated with a similar concentration of lutetium revealed a Hf-176:Hf-177 ratio of 0.282213 +/- 0.000023. The measurement of each mixed sample used approximately 400 ng of hafnium.