Determination of traces of heavy metals in positively charged inorganic colloids in fresh waters

Summary Determination of Traces of Heavy Metals in Positively Charged Inorganic Colloids in Fresh WatersAfter removal of suspended particulate matter by centrifugation followed by filtration through 0.4-m membrane filters, humic substances and other negatively charged species are sorbed on a small column of macroreticular weak-base anion exchanger DEAE-Sephadex A-25 at fast flow rates. Positively charged inorganic colloids pass through the column and are collected on a 0.015-m membrane filter, which is then ultrasonically treated with 1M nitric acid for the determination of copper, lead and cadmium by differential pulse anodic stripping voltammetry with a static mercury drop electrode. Up to O.2g 1^–1 of the heavy metals are found in positively charged inorganic colloids in river, pond and tap waters.