Method for isotope ratio drift correction by internal amplifier signal synchronization in MC-ICPMS transient signals†
The measurement of isotope ratios by Multi Collection Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) in transient signals often shows a drift of the isotope signal ratio during signal acquisition. This “isotopic drift” is generally related to the small and distinct time lags between the responses of the amplifiers involved in the Faraday detector configuration. In this work, a method of synchronization of transient isotope signals for a duration of a few tens of seconds is proposed in order to: (1) quantify the time lags between the amplifiers using the ratios of the raw isotope signals and (2) correct the isotope ratio drifts. The method was successfully tested on lead isotope ratio measurements obtained from two different multi-collector mass spectrometers and setups (flow injection with direct injection and gas chromatography). This approach offered a precise determination of the time lag between the different amplifier systems and an effective correction of the isotope ratio drift. The performances of the methods traditionally used for isotope ratio calculation of transient signals were also compared before and after isotope ratio drift correction.