I have solved a structure (using molecular replacement) of metallo-enzyme  which may have Zn or Ni at its active site. I  collected data at in-house CuKa radiation. Now, I am able to locate the active site metal ion preciously but I am not able to differentiate whether it is Zn or Ni. I computed anomalous difference map and I got good anomalous map also. But still there is ambiguity, since Zn and Ni have closest F" values at CuKa radiation ( For Zn = 0.68 and For Ni = 0.51). But both, Zn and Ni have different F' values at CuKa radiation ( For Zn = -1.61 and For Ni = -3.07).

My question is that,

Can we used F' value information to differentiate metal ions?.

Is it possible to find whether I have Zn or Ni at active site of my enzyme using  crystallographic technique?.