In IMAC purification using Ni-NTA, Co-NTA, Ni-Sepharose 6 fast flow, His-Link, Ni-TED..., the important concentration of imidazole used in elution steps will provoke a leakage of heavy metal ions from any metal chelate resin column...
Heavy metal ions are known toxic for cell growth as well as animal health.

References:

1) Environ. Toxicol. Chem. 2004 Jan; 23 (1) : 86-92.
2) J. Biol. Chem., Sep 1986; 261 : 14840 - 11848
3) J. Biol. Chem., Apr 2003; 278 : 12826 - 12833.
4) J. Biol. Chem., Sep 2004; 279 : 40337 - 40344.

1. Add some PMIB (polyvalent metal ion binding resin) cake to your protein solution.
2. Mix gently for 5 minutes.
3. Stand 1-2 minutes and filter off the metal chelate PMIB from your protein solution which then becomes totally free of heavy metal ions.

For details on PMIB, see http://www.affiland.com/imac/pmib.htm.

1. 1 patented PDC kit for selecting the appropriate metal ion to be chelated, composed of
1. 1 ml of Cu-PDC^R resin column
2. 1 ml of Zn-PDC^R resin column
3. 1 ml of Ni-PDC^R resin column
4. 1 ml of Co-PDC^R resin column
and
5. 2 x 100 ml of Washing Buffer A (the chemical formula will be provided with the order)
6. 2 x 100 ml of Washing Buffer B (the chemical formula will be provided with the order)
7. 1 x 100 ml of Elution Buffer E (the chemical formula will be provided with the order)
8. 1 x 100 ml of Elution Buffer F (the chemical formula will be provided with the order).
2. 1 x 25 ml of PMIB for removing heavy metal ions from protein solutions eluted by imidazole containing Elution Buffers, without loss of protein content.
3. 1 x 25 ml of PDC resin, free of metal ions for scaling up the purification of your his-tagged protein.

For details on PDC and PDC kit, see http://www.affiland.com/imac/pdc6x.htm.