Simultaneous determination of cobalt(II) and Ni(II) in water and soil samples with sequential injection analysis Original Research Article

The discontinuous nature of the sequential injection technique makes it ideally suitable for kinetic determinations. One of the advantages of kinetic analysis over equilibrium methods is the possibility of carrying out simultaneous determinations based on the different rates of their reactions with a common reagent. The different rates of the pseudo-first order dissociation of the citrate complexes of cobalt(II) and nickel(II) at pH 8.00 are used as a basis for the kinetic determination of these ions at trace levels in water and soil extracts. The reactions are followed by measuring the absorbance of complexes of the metal ions with 4-(2-pyridylazo)resorcinol (PAR) which are formed in a subsequent rapid reaction. EDTA is added to mask the major interferences. The proposed system is fully computerised and is able to monitor Co(II) and Ni(II) in samples at a frequency of 11 samples per hour with a relative standard deviation better than 1.2%. The detection limits are 0.14 and 0.20 mg/l for Ni(II) and Co(II) respectively.