High throughput isotope abundance ratio determination based on simultaneous ion counting and waveform averaging

Abstract

The quantitative accuracy and throughput performance for the newly developed hardware-based simultaneous ion counting and waveform averaging (AVG) in a time-of-flight (TOF) mass spectrometer was studied. The peak detection (PKD) algorithm was used for ion counting instead of voltage threshold detection method that is widely used in ion counting techniques. The silicon isotope abundance ratios were determined by the ion counting with ± 4 % uncertainties relative to the known isotope ratios. The measurements were carried out at relatively higher count rate condition (40 % which means that 0.4 ions arrived at the detector for each TOF trigger), but no systematic errors observed, which indicates the PKD algorithm was able to resolve two or more ions detected simultaneously compared to a simple voltage threshold detection algorithm. An excellent linear response was observed between PKD-based ion counts and the peak area determined by AVG waveform for 2 orders of magnitude. By using peak area based on AVG waveform for higher abundance ions and ion counting based on PKD for lower abundance ions, the silicon isotope abundance ratios were determined with the same analytical precision at one-tenth of the analysis time required for the ion counting alone.