Uncertainties on lead isotope analyses:deconvolution in the double-spike method

A weighted least-squares method is used to generate the `trueʹ lead isotopic composition from measurements on unspiked and spiked aliquots of a sample using the double-spike method. A form for the weighting based on theoretical mass spectrometer errors is used.The least-squares approach is more reliable for this deconvolution of lead isotopic compositions than current methods, and allows uncertainties and correlations on the true isotopic composition to be estimated, a feature of importance in many applications. The approach allows the prediction of run parameters for `optimumʹ spike analysis.