for ϳ48 hours at 230°C. After dissolution, the PGEs were isolated from one another and the bulkrock matrix by anion-exchange chromatography [M. Rehkä mper and A. N. Halliday, Talanta 44, 663 (1997)]. The pure PGE fractions were then analyzed with a Plasma 54 multiple-collector inductively coupled plasma mass spectrometer [A. N. Halliday et al., Int. J. Mass Spectrom. Ion Processes 146/147, 21 (1995)]. Multiple analysis of Iceland basalt sample BTHO and Alexo komatiite sample KAL-1 demonstrate

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... at our techniques achieve external reproducibilities of ϳ1.5 to 9% for the PGEs in the concentration range from parts per billion to parts per trillion. Duplicate analysis of two peridotite samples (OMX-8 and C235A) indicate a somewhat lower reproducibility (Յ15%), probably owing to the heterogeneity of the coarse-grained rocks. The PGE ratios of the duplicates, however, were identical to within 1 to 8%. Blanks for the Cameroon Line samples, digested with conventional Carius Tubes, were Ͻ10 pg/g for Ru, Pd, and Ir and 100 to 200 pg/g for Pt. Northern Tanzanian xenoliths were digested with the use of a modified Carius Tube design, and this technique achieves blanks of Ͻ15 pg/g for all analyzed PGEs (M. Rehkä mper, A. N.