Optimization of multicollector isotope-ratio measurement of strontium and neodymium

For isotope-ratio analyses of Sr and Nd whose precisions are constrained by amplifier and ion-counting noise, significant improvements in efficiency/precision can be realized by appropriate choices of peak vs. background measurement times, peak-jumping modes, and ratios for fractionation normalization. For Nd, theoretical limits on internal precision predict that the time-efficiency of dynamic analyses should be similar to that of static in most cases (slightly better in others), and that for Sr, dynamic analyses should be actually more efficient than static. Equations for the optimum mix of background times and peak-top times are given.