Sample Storage Artifacts Affecting the Measurement of Dissolved Copper in Sulfidic Waters

Abstract

Sample preservation and storage procedures (acidification with HNO(3) and storage in plastic bottles) normally employed prior to the determination of dissolved Cu in sulfidic waters were compared with sample preservation involving the initial oxidation of sulfide with H(2)O(2) or S(2)O(5)(2-) followed by acidification. Acidification alone was demonstrated to be inadequate and resulted in a significant underestimation of dissolved Cu (losses ranging from 50% to >90%). Similar losses were observed in both polyethylene and Teflon storage bottles. Experiments suggest that losses of copper occur following sample acidification owing to the formation of stable copper sulfide phases which adsorb onto container surfaces. It is therefore recommended that an oxidative pretreatment step is carried out prior to the acidification of porewaters collected for metal analysis. The results of this study suggest that much of the previous data reporting dissolved Cu concentrations in sulfidic waters and porewaters may be in error.