Search

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 possibility 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. [ABSTRACT FROM AUTHOR]

This paper presents a practical guide to an optimized analytical procedure for the reliable quantification of trace element concentrations in fluid inclusions hosted by natural minerals, using laser ablation inductively coupled plasma mass spectrometry (ICP-MS). With the improved sensitivities of modern ICP-MS instrumentation, more stringent guidelines for cleaning and contaminant reduction become decisive in extending the limits of trace element analysis, particularly for dilute fluids and smaller inclusions investigated by highly sensitive sector field ICP-MS. We have identified three sources of contamination that limit the recording and quantification of low-count signals, namely: (1) the carrier gas quality that affects the continuous instrumental background. (2) The material and cleanliness of the ablation cell, connection tubing material, and sampler and skimmer cone, all of which may cause a falsely elevated signal during ablation. (3) Contamination of the sample surface during its preparation and from the deposition of previously ablated material, including aerosols produced during extended ablation of an ICP-MS tuning material. Contamination from these sources can overlap with the host mineral and with the fluid inclusion signal. Based on extensive test experiments, we propose a workflow that allows minimization of these contamination contributions and optimizes representative sampling and quantification of fluid inclusion data. For example, Au and S in low-density vapor-dominated inclusions may be quantified down to a few ng g−1 and a few hundred μg g−1, respectively. [ABSTRACT FROM AUTHOR]