Pulse polarographic determination of trace amounts of cobalt (II) by complex formation with calcon

Some aspects of the polarographic reduction of sodium 1-(2-hydroxy-1-naphthylazo)-2-naphthol-4-sulphonate (trivial name: calcon or Eriochrome Blue Black R), as observed when using differential pulse polarography (d.p.p.) and alternating current polarography (a.c.p.), are described, as well as the polarographic behaviour of this compound in the presence of some metal ions. The peak that appears in the d.p.-polarogram due to the reduction of the cobalt (II) complex is the basis of a method for the determination of very small trace amounts of cobalt(II). The proposed procedure is rather selective (Ni(II) interferes, Mn(II) does not) and has a limit of detection of 7 g 1^–1 (minimum amount which can be determined 0.6 g Co(II)).