Isotopic precision for a lead species (PbEt4) using capillary gas chromatography coupled to inductively coupled plasma-multicollector mass spectrometry

Precision and accuracy of lead isotope ratios of a volatile lead species (PbEt4) were determined by coupling a capillary GC to a magnetic sector multicollector ICP-MS. PbEt4 was prepared by ethylation of a certified lead isotope solution (NIST SRM 981). Coupling was achieved by a transfer line, which allowed simultaneous introduction of a thallium standard solution to correct for mass discrimination. Seven isotopes (Hg-202, Tl-203, Pb-204, Tl-205, Pb-206, Pb-207, Pb-208) were monitored simultaneously with a transient resolution of 50 ms. Pb isotope ratios for the PbEt4 peaks were calculated using transient peak integrals of each isotope signal. Absolute detection limits were 20 (Pb-204), 0.7 (Pb-206), 1 (Pb-207) and 0.3 pg (Pb-208). Precision was assessed for five replicate injections of PbEt4 in iso-octane, corresponding to a total amount of 300 pg of Pb. Precision of isotope ratios for Pb-206, Pb-207 and Pb-208 were better than 0.07% (RSD), with ratios including Pb-204 being one order of magnitude worse. Accuracy using mass bias correction via Tl-203/(TI)-T-205 ranged from 0.18% for Pb-208/Pb-206 to 0.9% for Pb-208/Pb-204. (C) 2001 Elsevier Science B.V. All rights reserved.