How can I purify very small amounts of 6xHis-tagged protein using Ni-NTA technology?
FAQ ID -134

When working with small amounts of 6xHis-tagged protein in dilute solution, such as proteins expressed in mammalian cells or secreted into cell-culture medium, we recommend using Ni-NTA Magnetic Agarose Beads.

The total binding capacity of Ni-NTA Magnetic Agarose Beads is 3 µg of protein per 10 ul of magnetic bead suspension. Adjusting the amount of beads to the amount of 6xHis-tagged protein to be captured is crucial for optimal performance. The small elution volumes used provide high 6xHis-tagged protein concentrations, and allow detection of the purified proteins using Coomassie-stained SDS polyacrylamide gels.

Please see protocol 15 in the QIAexpressionist Handbook for detailed descriptions of a procedure to purify 6xHis-tagged proteins from transfected mammalian cells.