Deconvolution of the isotopic drift in LC-MC-ICPMS coupling: a new tool for studying isotope fractionation induced by sample introduction techniques

Abstract

On-line hyphenated methods between Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) and a variety of introduction techniques (liquid and gas chromatography, laser ablation…) provide transient signals with specific time-windows. It is now well-known that the isotope ratio drift which is observed during transient signal acquisition is generated from the MC-ICPMS detection system, the introduction techniques, or a combination of both parameters. In this work, the Nd isotope ratios were investigated through a coupling of MC-ICPMS with Liquid Chromatography (LC). The purpose was to dissociate the isotopic drift coming from the detection system from the drift caused by the introduction technique by using raw isotope data. To this end, the time constants of the MC-ICPMS amplifiers were used, and the isotope drift generated by the detection system was successfully corrected. After this correction, the isotope drift coming exclusively from the LC was highlighted. The use of the Method of Internal Signal Synchronization (MISS) allowed the correction of the chromatographic drift and the calculation of a time lag between the Nd isotopes of 0.0036 s amu⁻¹. This is the first time that for an isotope fractionation caused by a specific physicochemical process the time lag between the isotopes was calculated. We believe that the calculation of time lag values between the isotopes could be a simple and robust method opening up new possibilities for the study of isotope fractionations generated by different introduction techniques directly coupled with MC-ICPMS.