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 deoxygenation of freshwater before in situ voltammetric detection of trace elements 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 compared 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 long-term stability (maximum time tested 1 month), (iii) no formation of insoluble oxidized chemical compounds adsorbed on the external silicone tubing wall that may interfere with the O-2 diffusion, and (iv) easy in situ applications thanks to the convenience of chemical gel for transport and pressure compensation. Detailed description of the construction of the system as well as the systematic laboratory tests performed to optimize its performance 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 removal device coupled to a submersible voltammetric probe. The results indicate that the online oxygen removal system is robust and efficient for in situ, online deoxygenation and allows reliable subsequent voltammetric measurements of trace metals present at sub-nM level in oxygen saturated freshwater.