New perspectives on the use of triple quadrupole ICP-MS (laser and solution) systems for geochemical studies

Abstract:

Triple quadrupole ICP-MS (QQQ) systems are becoming more common in ICP geoscience laboratories. In addition to better sensitivity, when compared to old single quadrupole ICP-MS, they have the advantage of having a mass sorter before the collision cell to more efficiently remove isobaric interferences. We recently established a LA-ICP-MS lab in the School of Earth and Space Exploration at Arizona State University that hosts the new Agilent 8900 QQQ. This instrument is coupled to either a Teledyne Analyte G2 laser, for in-situ work, or a Cetac Aridus 3 Nebulizer, for solution work. We have tested several common geoscience applications, such as analyses of elemental composition in minerals (e.g. Sr-in-plagioclase), U-Pb dating and Ti-in-zircon analyses. Our results so far show the following: 1) QQQ systems have much better sensitivity than regular single quadrupoles, even when run as a single quadrupole in no-gas mode. Our Sr-in-plagioclase laser ablation analyses show better accuracy and reduction of errors by greater than a factor of two. This holds true even for spot sizes as small as 5-10 μm, when compared to the 25-100 μm spot size analyses used in recent literature for similar applications using single quadrupole systems. By reducing the spot size while simultaneously increasing the precision, we can improve the spatial resolution of transects across grain boundaries, enabling more accurate diffusion modeling and determination of volcanic timescales. 2) Addition of NH₃ gas, a mass-additive gas only available in QQQ systems, allows full suppression of the Hg-204 interference on the Pb-204 peak, greatly reducing the background counts and improving U-Pb dating analyses. 3) Addition of O₂, another mass-additive gas only available in QQQ systems, and H₂ in the collision cell allow suppression of the Zr-96²⁺ interference on Ti’s most common isotope, Ti-48, in Ti-in-zircon analyses, allowing more precise determination of Ti concentration. 4) Long runs of over 36 continuous hours show little to no drift, highlighting the amazing stability of the QQQ system. Our results therefore illustrate the amazing potential of QQQ ICP-MS systems for use in geosciences, demonstrating better handling of isobaric interferences, better sensitivity and high-quality data acquisition.