Determination of Co(II) by chemiluminescence after in situ electrochemicalpre-separation an a flow-through mercury film electrode

A novel method of electrochemical pre-separation of Co(II) before detection by chemiluminescence is reported together with the associated instrumentat ion. The Co(II) ions were selectively pre-separated on a mercury film elect rode (MFE) by on-line reduction, then the accumulated metal was oxidised an d selectively stripped back into the flowing solution as Co(II). These seco ndary ions were quantified as a result of their catalytic activity on the c hemiluminescent reaction between luminol and hydrogen peroxide that was als o induced on-line. The whole sequence was carried out in an automated flow- through system, in which the electrochemical pre-separation of metals was p erformed in either continuous flow or flow injection analysis (FIA) regimes . The scope of the method, both in terms of selectivity and sensitivity, ha s been demonstrated and the quantitative determination of Co(II) by the pro posed method has been investigated. For a period of continuous flow pre-sep aration of 4 min, the calibration curve for Co(II) was linear up to a conce ntration of 100 mug 1(-1), the relative standard deviation was 4% at the 20 mug 1(-1) level and the limit of detection was 0.5 mug 1(-1) (at the 3 sig ma level). The method was applied to the determination of the cobalt conten t in a high purity iron sample.