A FLOW CELL FOR ONLINE MONITORING OF METALS IN NATURAL-WATERS BY VOLTAMMETRY WITH A MERCURY DROP ELECTRODE

A cell was developed to enable flow analysis with voltammetric detecti on using a hanging mercury drop electrode (HMDE). The flow cell has a bore of 0.7 mm in which the mercury drop is centred, and has ports for a reference and a counter electrode, and for the capillary of the HMD E. The mercury drop has a diameter of 0.46 mm and a surface area of 0. 67 mm(2). Approximately 60 measurements are carried out per hour, a te n-fold increase compared with automated analysis using a conventional voltammetric cell. The flow cell is combined with on-line UV-digestion to destroy organic matter, a peristaltic pump to carry sample and rea gents, on-line de-oxygenation, and a three-way valve for standard addi tions to produce a system for on-line metal analysis. The system was t ested using on-line determinations of cobalt during a cruise in the No rth Sea. The sensitivity of the system was intermittently calibrated u nder on-line conditions by switching to a reagent stream with added me tal. The distribution of cobalt along the coast was correlated to geog raphical position and salinity, and possible sources of the metal coul d be evaluated. The possibility of integration with other high resolut ion measurements illustrates the advantage of on-line monitoring of tr ace metals by flow analysis with detection by cathodic stripping volta mmetry (CSV).