Sample purification Sample Clauses

Sample purification. Samples were acidified by adding 1 mL of concentrated HNO3. They were then evaporated to dryness in large PFA Teflon beakers in several steps (volumes depending on Fe, Cu, Zn concentrations, roughly varying between 50 and 700 mL). A few mL of concentrated HNO3 was added to the sample and evaporated at 130 °C to dissolve any solid remaining in the water. Similarly, they were taken up in 1 or 2 mL of concentrated HCl and evaporated at 130°C. Fe, Cu, and Zn were then separated following the method described by Xxxxxxxx et al. (1999), with volumes adapted to the sized of our PFTE columns of 4 mm (internal diameter) by 5 xx xxxx. Before loading in the column, samples were centrifugated and the remaining insoluble salts were left in the tubes. For Cu, the separation was repeated a second time for higher purification. Prior to this study, yield tests were carried out at ETH Zürich to ensure that none of the element of interest was remaining in the undissolved salts. Re-dissolution of seawater salts also evidenced that they do not trap any Cu and Zn. Pure fractions of Fe, Cu, and Zn were then evaporated at 130 °C, dissolved in 0.5 mL of concentrated HNO3 to eliminate any potential trace of organics, and evaporated to dryness at 130°C. For analysis, all samples were dissolved in 3% HNO3 (0.67 M). Though all sample trace element concentrations were analysed by ICP-MS prior to purification (section 2.2 and 2.3), concentration of pure fractions were tested again at this stage to ensure concentration matching with the standards at the time of isotope analysis.