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Abstract
Voltammetric detection of metals in natural waters suffers from interference by dissolved oxygen. We describe here a deoxygenation method suitable for flow analysis with detection by cathodic stripping voltammetry (FIA-CSV). The apparatus is based on the permeation of oxygen through semi-permeable tubing (silicone, Poreflon and others) into an oxygen-free chamber. Two methods of oxygen removal are proposed: in the first oxygen is removed physically from the chamber by flushing with nitrogen at a rate of 50 ml min −1; in the second oxygen is removed chemically by filling the chamber with an aqueous solution of a reducing agent (Na 2SO 3 or other compounds). At a fixed sample flow rate of 1 ml min −1, the length of the tubing is the main parameter which affects the deoxygenation efficiency, as it determines the residence time of the sample. 98% oxygen removal is achieved using 3 m tubing (36 s residence time). A removal of 90% of oxygen (1 m tubing and 12 s residence time) is sufficient to obtain a background current similar to conventional (batch) voltammetric systems and reproducible metal (copper and cobalt) peak heights are obtained at low metal concentrations. This enables the determination of trace metals by flow analysis with voltammetric detection at concentration levels encountered in uncontaminated seawater.
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