The cOmplete His-Tag purification resin is a high-capacity immobilized metal affinity chromatography matrix for convenient single-step purification of His-tagged protein. Compatibility with large amounts of EDTA and DTT allows optimization of buffers for protein stability and solubility. As leakage of toxic nickel is reduced, proteins are protected from oxidation and aggregation. The cOmplete resin also allows for multiple re-use without recharging nickel ions.