Preliminary assessment of laser ablation inductively coupled plasma mass spectrometry for quantitative multi-element determination in silicates

Abstract

A Nd:YAG (yttrium aluminium garnet) laser was used to ablate pressed powder pellets of seven silicate rock reference materials for sample introduction into an inductively coupled plasma mass spectrometer. Laser operating parameters, such as mode (fixed-Q or Q-switch), energy and number of shots per site were optimized to meet the criterion of maximum analyte signal without excessive loading of the plasma with ablated material. To compensate for differential laser sampling (i.e., variable amounts of material being removed during each analysis)⁵⁵Mn was used as an internal standard for multi-element determinations and ¹³⁷Ba for the rare earth elements (REE), Hf, Ta and W. Relative responses for the major elements indicate that the chemistry and mineralogy of individual rock samples influence the ablation behaviour and that samples with very similar chemical and mineralogical compositions exhibit similar elemental sensitivities. Alkali, alkaline earth and hydride-forming elements also show similar behaviour to the major components. Multi-element detection limits were typically less than a few hundred ng g^–1. The accuracy of major element determinations, for the materials studied, was generally better than ±5% relative with a precision of 10% relative standard deviation (RSD). Trace elements in Groups I, II, III, REE, volatile elements or those which exhibit refractory characteristic, displayed good accuracy, with precision of generally <10% RSD. The quantitative determination of major and trace elements in silicate rocks is therefore possible, providing that standards and samples are closely matched both in terms of bulk chemistry and physical (mineralogical) composition.