Determination of lead isotopic ratios in Greenland and Antarctic snow and ice at picogram per gram concentrations

Ultra-clean procedures have been developed which allow the isotopic composition of picogram quantities of lead to be measured in snow and ice from Greenland and Antarctica. Ultra-clean collection, storage and processing techniques were used to analyse samples containing as little as ca. 2 pg Pb/g. The concentration and isotopic composition were measured simultaneously by isotope dilution mass spectrometry using a lead spike enriched in205Pb. Although the precision of the isotopic ratios improved with the size of the sample, a precision of ca. 0.2% could be achieved on a few tens of pg of Pb, enabling small differences in isotopic composition to be resolved in deep ice cores and surface snow.