Development and application of inductively coupled plasma-mass spectrometric techniques for the precise measurement of trace elements and lead isotopic compositions in geological materials

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful analytical technique, regarded as one of the most successful in atomic spectrometry, and widely used for measurement of a wide range of trace elements in geological materials. In general, this established technique has the merits of high sensitivity, fast analysis capacities, true multi-element abilities, and a very large dynamic linear concentration range. Sample preparation is also relatively simple. This study has systematically investigated analytical performance characteristics of a high resolution (HR)-ICP-MS instrument (Finnigan Mat Element, Germany). This instrument has been found to be more sensitive, with less spectral interferences (due to the pre-defined setting of different resolutions) than quadrupole instruments. It has been found that only a single internal standard is sufficient to compensate for the instrumental drift during an analytical sequence. The detection limits for some trace elements studied were found to be as low as pg g-1 levels in solution. To obtain accurate analytical results using ICP-MS, complete sample dissolution is required. Decomposition techniques for the dissolution of different types of geological materials have been studied. Savillex Teflon beaker HF/HN03 digestion has been found to be sufficient for the complete dissolution of basaltic samples. High pressure HF/HC104 digestion (PicoTrace® TC-805 digestion system, Bovenden, Germany) can be used for the dissolution of ultramafic rocks such as dunite and peridotite, in which many geologically useful trace elements are at very low abundance, and also granites (which may contain difficult to dissolve zircon) and magnetite-rich samples. It has been found that a lithium tetraborate fusion method allows complete dissolution of different types of geological materials, but this method precludes analysis of volatile elements due to the high fusion temperature (approximately 1000 °C). The sodium peroxide sinter method may enable fast determination of Y, Sc and REE in different types of geological materials. However, neither the lithium tetraborate fusion nor sodium peroxide sinter method can be used for the measurement of low abundance geological samples, due to the lack of ultra-pure reagents. In general, the microwave digestion method has been found to be unsuitable for the total decomposition of geological materials. Systematic investigation of chelates between several complexing reagents (citrate, tartrate, EDTA and DTPA) and Zr, Nb, Ta, Hf, Th and U ("high field strength elements" - HFSE) has shown that DTPA can form stable HFSE complexes in solution. These prevent the hydrolysis of HFSE and hence allow the accurate determination of HFSE in geological materials. A complexing method has been developed, which coupled with an appropriate digestion method and ICP-MS, can lead to the accurate determination of HFSE at different levels (particularly higher than 1 µg g-1 of Nb and Ta) in geological reference materials. As a comparison study and a geological application of the ICP-MS techniques developed in this study, trace element concentrations of seventeen oceanic basalt glasses from Macquarie Island have been measured by both solution-based HP-ICP-MS & quadrupole ICP-MS and solid sampling-based laser ablation ICP-MS. The majority of elements measured by the three analytical protocols showed discrepancies of