On-line determination of copper and nickel with in-situ complex formation

On line determination of copper and nickel with in situ complex formation 

The mobile phase composition 70% 30% acetonitrile acetate buffer (0.02 M, pH 6) gives adequate separation of Cu(dtc)2 and Ni(dtc)2. 0.005-0.01 M NaNOg is added to the solvent to provide adequate conductivity for electrochemical detection. The mobile phase also contains between 10 and 10 M dtc for the purposes of in situ complex formation. Addition of ligand to the solvent does not affect the retention volumes of these compounds. 

Both copper and nickel react very rapidly with either dedtc or pydtc to form the corresponding metal-dithiocarbamate complex. Work in a conventional electrochemical cell as described previously, indicated that a 10-fold excess of ligand was required for fast and complete complex formation. Under these conditions a short length of coiled tubing (20 cm), inserted between the injector and the guard column, allows sufficient time for complete reaction. 

At around +0.1 V vs Ag/AgCl, oxidation of the free ligand occurs to produce thiuram disulfide. 

At more positive potentials, the previously described reversible Cu(dtc 2 [Cu(dtc)2l + e process and the irreversible Ni(dtc)2C oxidation process given in equation (5) are observed. 

---