[BAL]

I dont know if one instrumental method is allowed for thread, the best way for determinate Caocium in milk is atomic absortion, but also there are others ways too.I don't remember very well the procedure but you can titrate Calcium wtih EDTA and determinate the final point using and ion selective detector, or redox system to see the first oxalate excces, even you can you and conductivity detector, this is very use because you just need and condutivity cell and titrate the calcium with oxlate, the conductiity will go changing, after the end point you will see a drastic chance in the slope.
These are titration, but you use an electrode to see your final point, is very fast and precise.