Advantages of a fast-scanning quadrupole for LA-ICP-MS analysis of fluid inclusions
Résumé
For the past 20 years, LA-ICP-MS has been the method of choice to quantify element concentrations in fluid inclusions hosted in geological samples. However,
the ablation of fluid inclusions typically produces short, transient signals that are difficult to representatively sample with sequential analysis inherent to single
collector ICP-MS instruments, especially considering small inclusions (<20 μm) and/or low-concentration elements (<10 μg.g-1). This issue can be overcome by
significantly reducing quadrupole settling times, allowing faster cycling through a given element list at constant duty cycle and therefore, better temporal
resolution of the signal. In this note, we present results from already well-characterized fluid inclusion assemblages performed with a “fast-scanning”
quadrupole ICP-MS, i.e. characterized by extremely short settling times (default 0.2 ms and down to 0.065 ms). This capability, which does not impede basic
instrument performance, improves the results of LA-ICP-MS fluid inclusion analyses in three ways. First, it extends the possiblity to accurately and reproducibly
quantify element concentrations to fluid inclusions down to <10 μm in size, with absolute detection limits in the same range as using a conventional
quadrupole. Second, it releases the need to compromise between full chemical characterization of the fluids and accurate determination of some key elements
of interest, as short settling times offer the possibility to rapidly scan through extensive element lists (e.g. 52 elements cycled in 52 ms at 80% duty cycle in
the tests presented here). Third, it improves accuracy and precision for analytes hosted in small daughter crystals in assemblages of complex, polyphase fluid
inclusions.
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