Lead isotope ratio analysis by inductively coupled plasma sector field mass spectrometry (ICP-SMS) in soil digests of a depth profile

The application of inductively coupled plasma sector field mass spectrometry (ICP-SMS) (Finnigan-MAT, Element) to lead isotope ratio determination in soil samples is described. Discrimination of anthropogenic and geogenic lead sources requires both precise and accurate isotope ratio determination and also high versatility due to the complex matrix, which is typical for soil extracts. Moreover, a high sample throughput is required. ICP-SMS could therefore be implemented as the method of choice. Precision of isotope ratios of Pb-206/Pb-207 of better than 0.03% was obtained throughout the investigations in a concentration range of 5-50 ng g(-1) in solution. Accuracy was illustrated by using the NIST SRM 981 isotopic ratio reference standard and was 0.03% for both the Pb-207/Pb-206 and Pb-208/Pb-207 ratios. In order to differentiate between anthropogenic and geogenic sources of lead in soils, both lead concentration and isotopic composition were determined by ICP-SMS along a soil profile collected from a Dystric Cambisol in Eastern Austria. Along the soil profile, a significant change of lead isotopic composition could be detected, showing the difference between anthropogenic (surface) and geogenic (parent rock) sources. Along with the total concentration of lead and other soil properties, the contribution of anthropogenic sources to the lead concentration of soils and their participation in lead mobilization can be estimated.