The Advantages of TOF for ICP-MS Analysis of Fluid Inclusions

In a recent publication from ETH, Matthieu Harlaux and co-workers compare the performance of quadrupole (Q), sector field (SF), and time-of-flight (TOF) based ICP-MS for the analysis of fluid inclusions in minerals.

“Capabilities of sequential and quasi-simultaneous LA-ICPMS for the multi-element analysis of small quantity of liquids (pl to nl): insights from fluid inclusion analysis”  J. Anal. At. Spectrom., 2015

Fluid inclusions were sampled with different laser ablation technologies, chosen based on the spectral acquisition rates of the mass analyzers. Due to their speed limitations, the scanning QMS and SFMS where coupled to commercial LA-cell technology with washout times of about 1 s. The TOFMS, which records all mass/charge values simultaneously, was used with a small volume tube-type ablation cell having washout times as short as 30 ms.

ICP-TOFMS excelled for the analysis of small fluid inclusions

  • ICP-TOF recorded significantly more data points per inclusion and more isotopes of interest. Even the complex signal structure of multi-phase inclusions can be deciphered and related. e.g., to originate from aqueous phase or from halite, magnesium hydroxides, hematite or uranium crystallites respectively.
  • ICP-TOFMS generally provided the best precision for all types of analyzed inclusions
  • ICP-TOFMS demonstrated the best detection limits over the entire mass range for small inclusions of <10 µm, especially for heavy elements with m/Q >85 Th.[/fullwidth]

On paper the sensitivity of ICP-TOFMS for single element analysis is similar to QMS-based instruments and lower than SF-ICP-MS. But TOF is the only mass analyzer that simultaneously measures all mass/charge values and thus the only one which can be coupled to fast washout laser ablation equipment. Under ‘real world’ conditions with a reasonable set of measured isotopes and confronted with complex transient signals the TOFMS shows distinct advantages over the scanning instruments. The gain in S/N through reduction of aerosol dispersion leads to improved precision and even lower detection limits compared to QMS and even SFMS setups.