Evaluation of mixing devices and connection mode in the determination of Pb in glass using online isotope dilution laser ablation-ICP-MS

Abstract

Online isotope dilution laser ablation ICP-MS (ID-LA-ICP-MS) is considered a labor-saving, easy and accurate quantification technique when dealing with solid samples. However, in the mixing process of spike-sample aerosols, it is difficult for the aerosols to reach full isotopic equilibrium before being introduced to ICP-MS. Therefore, the poor and unstable mixing efficiency may result in an unstable isotope ratio, which cannot be accurately determined when using online ID-LA-ICP-MS. In this work, to improve the mixing efficiency and achieve a good isotopic equilibrium, four different mixing devices (devices A–D) were designed. Further, to comprehensively evaluate the mixing efficiency of the different devices, the signal sensitivity, trueness and precision of the blended ²⁰⁸Pb/²⁰⁷Pb ratio of each device in different connection modes (pre- or post-cell introduction of a ²⁰⁷Pb spike) were investigated. Of all the four devices, the assembly of device B in a pre-cell connection mode showed optimal performance in three aspects: (1) good trueness and consistency of the blended ²⁰⁸Pb/²⁰⁷Pb ratio; (2) good precision of the measured ²⁰⁸Pb/²⁰⁷Pb ratio (1.5–2.5%); (3) less signal sensitivity loss (0.6–0.7-fold less than in the post-cell mode). Using device B and a pre-cell connection approach, Pb in glass (NIST SRM610) was determined and a good agreement with the certified value was achieved. This work will help make the online ID-LA-ICP-MS method more accurate and precise.