Purification method and apparatus for purifying a gas stream by oxygen removal. The apparatus includes primary and secondary oxygen separation zones and tubular electrically driven oxygen separation elements. There are more elements in the primary zone than the secondary zone so that low concentrations of oxygen can be obtained in a purified stream and turbulent flow conditions can also be obtained that will permit purification to very low levels. In addition, a junction is provided to connect the tubular separation elements to metallic elements such as manifolds.