Improvements in Digestion Protocols for Trace Element and Isotope Determinations in Stream and Lake Sediment Reference Materials (JSd‐1, JSd‐2, JSd‐3, JLk‐1 and LKSD‐1)

Abstract

International audienceTotal dissolution is a critical step in geochemical analysis. Despite the number of published protocols, this issue still draws attention for sediment samples, which are particularly difficult to dissolve due to the common occurrence and high abundance of refractory phases such as zircon. We present tests of different chemical digestion procedures carried out on reference materials (RM) of stream (JSd-1, JSd-2 and JSd-3) and lake (JLk-1 and LKSD-1) sediments from the Geological Survey of Japan (GSJ) and the Canadian Certified Reference Material Programme (CCRPM). We demonstrate that the fusion technique is not appropriate for our studies as not all elements of interest were recovered and blank levels were too high to permit further Sr and Pb isotopic composition measurements. Similarly, conventional HF+HNO3 dissolution methods were not efficient enough for detrital samples. Our preferred method involved using high pressure Teflon® vessel bombs in association with HClO4. This protocol ensured a complete dissolution of the powder, as well as a complete recovery of trace elements. Moreover, blank levels were sufficiently low that Sr or Pb isotope compositions could be measured from the same mother solution. We also tested the homogeneity of RM powders by performing tests on various amount of powder

Comprehensive Chemical and Isotopic Analyses of Basalt and Sediment Reference Materials

“…Even if the reproducibility of our measurements for sediments was not as good as for the basalts, it was generally better than values reported in the literature (Imai et al. 1996, Lynch 1999, Révillon and Hureau‐Mazaudier 2009). Furthermore, our values obtained for all elements were always within the range of previously reported concentrations.…”

“…A possible explanation is that the dissolution was not complete and refractory minerals such as zircon, rutile and garnet remained undissolved. Indeed, in a recent paper, Révillon and Hureau‐Mazaudier (2009) showed clearly that incomplete dissolution of these sediments was extremely common and recommended the use of HClO 4 combined with HF in Parr bombs to achieve dissolution. Not only did we use this technique but we combined it with a first dissolution step in Savillex beakers using concentrated HNO 3 to destroy organic matter prior to dissolution of the silicate minerals in the Parr bombs.…”

“…Although this has only minor effect on the reproducibility of most elements, including Al 2 O 3 and Li, it has drastic effects on trace elements that are present at very high concentrations in some specific minerals: Zr and Hf in zircon, Nb and Ta in rutile and HREE in garnet. In their recent study of the same sediments, Révillon and Hureau‐Mazaudier (2009) encountered a similar problem involving heterogeneity of the powder and suggested that LKSD‐1 contained quartz grains that diluted all trace elements to different degrees, depending on the amount sampled for each dissolution. We agree that variable amounts of quartz could affect the concentrations of most trace elements, as quartz is basically devoid of all elements except for SiO 2 .…”

Method Development and Optimisation of Sodium Peroxide Sintering for Geological Samples

“…Successful digestion of garnet, sphene, spinel, zircon, rutile and chromite has been performed with acid attack in sealed polytetrafluoroethylene (PTFE) bombs heated at high temperatures (> 160 °C) for several days (Yu et al . , Révillon and Hureau‐Mazaudier ). Acid mixtures of different combinations have been applied for the digestion of refractory mineral phases.…”

“…A mixture of HF/HNO 3 /HClO 4 is frequently used and seems to be more effective for the dissolution of granitoid and sediment samples than HF/HNO 3 as reported in Pretorius et al . () and Révillon and Hureau‐Mazaudier (). The HF/HNO 3 /HClO 4 mixture boils at a higher temperature, and this does not just benefit the removal of HF but also increases dissolution efficiency.…”