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

Abstract

A weighted least-squares method is used to generate the 'true' lead isotopic composition from measurements on unspiked and spiked aliguots 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 'optimum' spike analysis.