Determination of thorium in environmental and workplace materials by ICP–MS

The paper outlines the advantages of the use of Inductively Coupled Plasma Mass Spectrometry (ICP–MS) over radiometric techniques to measure natural thorium, 232Th. Experimental parameters that must be taken into account in the sample digestion, preparation and ICP–MS analysis of environmental (soils, rocks, sediments) or workplace (thorium oxide, reference solutions) materials are described. The methods presented are applied to various reference materials, with the aim of providing suitable procedures to be useful for other important thorium containing materials (such as monazite sands or welding electrodes). The participation in a European Commission intercomparison exercise is detailed and a comparison with alpha spectrometry is made.