Solid-spiking isotope dilution laser ablation ICP-MS for the direct and simultaneous determination of trace elements in soils and sediments

Abstract

The direct and simultaneous determination of Cu, Zn, Sn and Pb in soil and sediment samples by femtosecond laser ablation inductively coupled plasma isotope dilution mass spectrometry (fs-LA-ICP-IDMS) has been accomplished in this work with the development of a solid-spiking sample preparation procedure. The total analysis time, in comparison with previous approaches, has been significantly reduced by developing a solid-spiking procedure based on the synthesis of a unique isotopically-enriched solid spike and the preparation of isotope-diluted blend pellets for each sample. The laser repetition rate and the ablation mode were carefully selected (10 kHz and the 2D scanning sampling mode, respectively) in order to reduce the effect of possible local inhomogeneities of the powdered samples on the precision of isotope ratio measurements. Special attention was focused on the heterogeneous distribution of trace elements in the isotopically-enriched solid spike and the isotope-diluted blend samples in order to assure that the measured isotope ratios remained constant (precisions lower than 10% RSD; n = 8). The proposed methodology was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials. The concentrations obtained by solid-spiking fs-LA-ICP-IDMS were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore the validity of the proposed solid-spiking procedure for a rapid and accurate analysis of solid samples.