Evaluation of detector dead time calculation models for ICP-MS

Four methods of pulse counting detector dead time calculation were evaluate d on two quadrupole ICP-MS instruments, using the criteria of ease of appli cation and accuracy (i.e., reliable measurement uncertainty). Three of the methods were based on measurements of the Pb-204/Pb-208 isotope ratio in th e NIST Standard Reference Material NBS-982, while the fourth method was bas ed on the comparison of pulse counting signals versus the corresponding ana log signals across a range of signal intensities. The uncertainty in the de ad time result derived from each method was evaluated and found to vary con siderably, with some approaches underestimating this parameter, while other s yielded large uncertainties. Overall, a method based on studies of the Pb -204/Pb-208 isotope ratio measured for different Pb concentration solutions , recalculated using different dead time settings (herein referred to as Me thod 2), was found to be the most suitable in terms of the specified criter ia, particularly with respect to its uncertainty evaluation.