Dear all, I am using Ni-NTA agarose (Qiagen) for purification of His-tagged proteins by gravity-flow chromatography. Given that this agarose is remarkably expensive I would like to re-use it. For that purpose, could anybody kindly provide a good protocol for stripping-off (and reloading) Ni2+? After a quick research in the internet, I only found something for prepacked His-trap AKTA-columns but also read about some doubts that such protocols can be used for the Ni-NTA agarose for gravity-flow. I would appreciate any help. Thanks.