Flowing stream coulometry

4 SEPARATION OF NICKEL AND COBALT BY COULOMETRIC ANALYSIS AT CONTROLLED POTENTIAL 

Reagents. Standard nickel and cobalt ion solutions. Prepare solutions of nickel and cobalt ion (ca 10 mgmL 1) from pure ammonium nickel sulphate and pure ammonium cobalt sulphate respectively. 

Pyridine. Re-distil pyridine and collect the middle fraction boiling within a 2°C range, viz. 113-115°C. 

Supporting electrolyte. Prepare a supporting electrolyte composed of l.OOM pyridine and 0.50M chloride ion, adjusted to a pH of 7.0 0.2 for use with a silver anode, or LOOM pyridine, 0.30M chloride ion and 0.20M hydrazinium sulphate, adjusted to a pH of 7.0 0.2, for use with a platinum cathode. A small background current is obtained with the latter. 

The electrode will of course be incorporated in a circuit similar to that previously described in which a potentiostat controls the potential of the working electrode and may also provide a counter-current facility to nullify the background current an electronic integrator will also be included. 

---