Hi... right now I'm taking an Analytics Lab course, and I have to quantify Calcium, Cadmium and Zinc from a real sample (pH acid). When I did qualitative, I found that I also have Fe, and Carbonate, Nitrate and Chloride ions. So far, I have this to Identify the cations:
1.- As my ph is acid, use AgNO3 to get rid of the chlorides
2.- Take the pH to basic conditions (should I get rid of the carbonates adding acid before? Which would be better , HCl or H2SO4?)
3.- Take pH to basic (I fear the calcium precipitates if I use sulphuric acid, or if i don't get rid of carbonates)
4.- Mask all but Ca with Cyanide
5.- Use EDTA to valorate Ca
6.- Unmask (formaldehyde, does it unmask Fe as well?) Zn and Cd.
7.- Titrate (ammonia medium) to obtain Cd and Zn together. Use diethyltiocarbamate (DDC) to mask Cd, and calculate de EDTA liberated.
I know it's kinda rough, but is what I've got so far. I hope anyone could help, at least telling me if it is OK so far, or by giving me any ideas. Thank you!!!