DETERMINATION OF LEAD ISOTOPIC-RATIOS IN GREENLAND AND ANTARCTIC SNOWAND ICE AT PICOGRAM PER GRAM CONCENTRATIONS

Ultra-dean procedures have been developed which allow the isotopic com position of picogram quantities of lead to be measured in snow and ice from Greenland and Antarctica. Ultra-clean collection, storage and pr ocessing techniques were used to analyse samples containing as little as ca. 2 pg Pb/g. The concentration and isotopic composition were meas ured simultaneously by isotope dilution mass spectrometry using a lead spike enriched in Pb-205. Although the precision of the isotopic rati os 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 .