A model for calculating the dead time and ion counter efficiency from thermal ionization mass spectrometry calibration curves

Abstract

Thermal ionization mass spectrometry (TIMS) is a widely used mass spectrometric technique for trace/ultra-trace isotopic analysis. For accurate isotope ratio determination, the detector dead time and ion counter efficiency have to be appropriately corrected for. Two methods of pulse counting detector dead time calculation were evaluated on a TIMS instrument. Both methods were based on the measurement of Sr isotope ratios in NIST standards and had similar performance in assessing the dead time for pulse-count detectors. In addition, one of the newly proposed methods in this manuscript can be used to simultaneously determine the dead time and ion counter efficiency of the pulse counting detector via the ratio measurement approach. The advantages of using the method presented here are firstly that both the detector dead time and the ion counter efficiency can be obtained simultaneously and secondly that the sampling time can be spent entirely on the isotopes of interest.