Determination of gold at the ultratrace level in natural waters

Abstract

Several methods for the preconcentration of dissolved gold in natural waters were evaluated for use with graphite furnace atomic absorption spectroscopy (GFAAS) or inductively coupled plasma mass spectrometry (ICP-MS). An anion exchange method prior to GFAAS, and a solvent extraction method prior to ICP-MS both proved to have similar recoveries, low limits of detection (0.4 and 0.2 ng l −1, respectively, for a 2-1 sample) and good reproducibility. Parallel analyses of particulate gold were also carried out by instrumental neutron activation analysis (INAA) with detection limits between 0.04 and 0.5 ng l −1 depending on the volume of filtered water, to provide a complete evaluation of transported gold. These methods were subsequently tested on stream, spring and adit water samples, to check the accuracy of methods for natural waters. Results obtained by ICP-MS and GFAAS on natural water samples were comparable. The maximum dissolved gold concentration was 3 ng l −1, and particulate gold formed less than 50% of the total amount of gold transported. No significant variation was found in the dissolved gold content of one spring water sample monitored monthly over a one year period.