Analysis of elemental distributions in minerals and rocks by microwave-assisted continuous leaching on-line with inductively coupled plasma mass spectrometry

Continuous on-line leaching with Inductively Coupled Plasma Mass Spectrometry (CL-ICP-MS) is a novel technique that can quickly assess the mobility and fractionation of elements in soils. It involves pumping different reagents sequentially through a micro-column containing the soil sample while continuously monitoring the released analytes by ICP-MS. Previous studies of CL-ICP-MS employed a high resolution ICP-MS (ICP-HRMS) instrument equipped with a micronebulizer to demonstrate its application to the analysis of minerals in ore samples. However, the long sample analysis time, from the slow mass scanning rate of HRMS, hinders its feasibility in exploration geochemistry.; Focused-microwave heating was used in combination with simultaneous multielemental detection through ICP-TOFMS (ICP-time-of-flight mass spectrometry) at a higher flow rate to speed up the continuous leaching of soils. Heating the micro-column to 90°C using focused-microwave energy significantly enhanced the release of analytes, by up to an order of magnitude. This was achieved without any increase in the time needed for the whole fractionation study, which is about 16 minutes and is substantially shorter than the several hours that are required for typical procedures using CL-ICP-HRMS.; Analysis of single minerals as well as a complex sample showed that the flow rate of reagents through the sample had an effect on the leaching profile, but the simultaneous application of microwave energy, which speeded up the kinetics of dissolution, essentially compensated for the shorter residence time, yielding profiles fairly similar to those obtained at low flow rate with a micronebulizer and ICP-HRMS.