PURPOSE: To remove dissolved oxygen with high efficiency by bringing a liquid contg. dissolved oxygen into contact with a chelating resin wherein ferrous ions are complex adsorbed by chelation.

CONSTITUTION: After a liquid contg. ferric ions is passed through a chelating resin to adsorb the ferric ions, a soln. of sodium dithionite is passed to form the chelating resin wherein ferrous ions are adsorbed by chelation. The treated water having ≤5ppb concn. dissolved oxygen can be obtained by passing a liquid wherein oxygen is dissolved through the chelating resin. The flow rate of the liquid can be increased by allowing the chelating resin to adsorb a trace amt. of polyvalent metallic ions such as Co, Ni, and Cr as a catalyst. The chelating resin can be applied to a comparatively high-concn. salt soln. as well as to demineralized water.