Lead isotopic analysis using a double spike

Variable mass discrimination limits the accuracy of lead isotopic analysis by single-filament surface ionization. It can be corrected to an accuracy of 0.1% by making an additional mass analysis of the sample mixed with a double Pb204, Pb207 tracer. The principles of the method are described and its use is illustrated by replicate analysis of the California Institute of Technology (CIT) common lead standard. Its accuracy is determined by the calibration of the Pb204/207 of the spike, which is here based on the National Bureau of Standards (NBS) equal atom Pb standard and by a comparison of the fractionation corrected CIT ratios with those observed by E. J. Catanzaro.