Major and trace element analysis of silicate rocks by XRF and laser ablation ICP-MS using lithium borate fused glasses: Matrix effects, instrument response and results for international reference materials

Major and trace element compositions of fifteen silicate rock reference materials have been determined by a combined XRF and laser ablation ICP-MS (LA-ICP-MS) technique on glasses prepared by fusing the sample with a lithium borate flux (sample:flux = 1:3). Advantages of this technique include the ability to measure major and trace element abundances on a single sample using a quick and simple preparation that attacks resistant phases such as zircon without the need for acid dissolution. The method is suitable for a wide variety of bulk compositions including mafic, intermediate and silicic rocks. Abundance-normalized mass response patterns (the ratio of signal intensity to element concentration) of the LA-ICP-MS analyses vary systematically with major element composition, demonstrating the presence of a matrix effect that cannot be compensated by normalisation to a single internal standard element. Increasing the sampling distance between the ICP-MS cone and the torch reduces the magnitude of this effect, suggesting that a mechanism related to residence time of ablated particles in the plasma may be at least partially responsible for the observed variations in mass response patterns. When using a matrix-matched calibration, agreement of the LA-ICP-MS results with published reference values or those obtained by solution ICP-MS is ≤ 10% relative. Analytical precision based on replicate analyses is typically ≤ 5% RSD. Procedural detection limits that include contributions from gas background and flux are 0.01-0.1 μg g ^-1 for the heavy mass trace elements (Rb-U). Major element analyses by XRF show excellent agreement with results obtained using a conventional heavy element absorbing flux. High quality major and trace element data for silicate rocks can be achieved by a combined XRF and LA-ICP-MS analysis of Li ₂B ₄O ₇/LiBO ₂ fused glasses provided an appropriate matrix-matched calibration is adopted.