In-line deoxygenation for ̄ow analysis with voltammetric detection

Voltammetric detection of metals in natural waters suffers from interference by dissolved oxygen. We describe here a deoxygenation method suitable for ̄ow analysis with detection by cathodic stripping voltammetry (FIA-CSV). The apparatus is based on the permeation of oxygen through semi-permeable tubing (silicone, Pore ̄on and others) into an oxygen-free chamber. Two methods of oxygen removal are proposed: in the ®rst oxygen is removed physically from the chamber by ̄ushing with nitrogen at a rate of 50 ml minÿ1; in the second oxygen is removed chemically by ®lling the chamber with an aqueous solution of a reducing agent (Na2SO3 or other compounds). At a ®xed sample ̄ow rate of 1 ml min ÿ1, the length of the tubing is the main parameter which affects the deoxygenation ef®ciency, 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 suf®cient 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 ̄ow analysis with voltammetric detection at concentration levels encountered in uncontaminated seawater. # 1998 Elsevier Science B.V. All rights reserved.