Submersible online oxygen removal system coupled to an in situ voltammetric probe for trace element monitoring in freshwater

A new online oxygen removal system specifically built to allow in situ deox ygenation of freshwater before in situ voltammetric detection of trace elem ents using a submersible probe is described. It is based on the permeation of oxygen through a silicone tubing surrounded by an enzymatic cross-linked O-2 scavenging gel. The main advantages of the enzyme cross-linked gel com pared to the chemical O-2 reducing solutions proposed in the literature for laboratory online deoxygenation coupled to other devices are as follows: ( i) ease of preparation and storage under normal room condition, (ii) good l ong-term stability (maximum time tested 1 month), (iii) no formation of ins oluble oxidized chemical compounds adsorbed on the external silicone tubing wall that may interfere with the O-2 diffusion, and (iv) easy in situ appl ications thanks to the convenience of chemical gel for transport and pressu re compensation. Detailed description of the construction of the system as well as the systematic laboratory tests performed to optimize its performan ce are reported. Examples of environmental applications are also given. In particular, in situ monitoring and profiling of Cu(II), Pb(II), and Zn(II) in oxygenated lake water have been performed using this new online oxygen r emoval device coupled to a submersible voltammetric probe. The results indi cate that the online oxygen removal system is robust and efficient for in s itu, online deoxygenation and allows reliable subsequent voltammetric measu rements of trace metals present at sub-nM level in oxygen saturated freshwa ter.