SAMPLE STORAGE ARTIFACTS AFFECTING THE MEASUREMENT OF DISSOLVED COPPER IN SULFIDIC WATERS

Sample preservation and storage procedures (acidification with HNO3 an d storage in plastic bottles) normally employed prior to the determina tion of dissolved Gu in sulfidic waters were compared with sample pres ervation involving the initial oxidation of sulfide with H2O2 or S2O52 - followed by acidification. Acidification alone was demonstrated to b e inadequate and resulted in a significant underestimation of dissolve d Cu (losses ranging from 50% to >90%). Similar losses were observed i n both polyethylene and Tenon storage bottles. Experiments suggest tha t losses of copper occur following sample acidification owing to the f ormation of stable copper sulfide phases which adsorb onto container s urfaces. it is therefore recommended that an oxidative pretreatment st ep is carried out prior to the acidification of porewaters collected f or 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.