Analysis of polyacrylamide gels for trace metals using diffusive gradients in thin films and laser ablation inductively coupled plasma mass spectrometry

摘要

A simple method for the analysis of polyacrylamide diffusive gradients in thin film (DGT) gels by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), employing a novel use of In-115 internal standardization, has been developed. This method allows the determination of Co, Ni, Cu, Zn, Cd, and Pb concentrations (at the DGT filter face) or fluxes in sediments at a spatial resolution of 100 mum. Single-layered gels, using an optimized laser defocus of 4000 mum at 400 mJ power, showed high precision (generally similar to10%) and a linear response during solution deployment. Of the elements Sc, In, Ba, La, Ce, and Tb, Ba most closely tracked variations in laser energy and showed the highest analytical precision but could not be used as an internal standard due to its elevated presence in natural sediments. Therefore, internal standardization, necessary to normalize data collected on different days, was carried out using In-115 contained within a second layer of backing gel and dried along with the analyte layer as a dual-gel disk. This multilayered gel standard required a laser defocus setting of 1000 mum and a laser power of similar to800 mJ. Analytical precision for a 64-spot ablation grid at 100-mum spacing similar to10%. Verification of this method was carried out on DGT sediment probes deployed in Priest Pot (English Lake District). Results obtained by conventional slicing techniques and aqueous elution agreed with laser ablation results when the different sampling areas were considered. The elution results varied by a factor of < 2, whereas the laser ablation technique showed a variability of similar to4, indicating localized elevated concentrations of Co. This higher resolution LA-ICPMS method could ultimately lead to an improved understanding of the geochemical processes responsible for metal uptake and release in sediments.