The effect of micellar media (cetyltrimethylammonium bromide) for complex formation reaction of cobalt and nickel ions with xylenol orange (XO) has been investigated. The order of reaction and the apparent activation energy have been determined. The sensitivity of ternary complex of cobalt(Ⅱ) and nickel(Ⅱ) are 4.4 and 8.6 times bigger than binary complex. In the meantime, the difference of the reaction rate of two complex was increased and the selectivity of reaction was improved obviously. A new analytical method hased on the reaction rate difference of two ternary complex, for simultaneous determination of cobalt(Ⅱ) and nickel(Ⅱ) was developed, the logarithmic extrapolation method with computer was used to calculate. This method has been applied to simultaneous determination of cobalt and nickel in samples with satisfactory results. The relative error for determinations of two components was within 4% and the relative standard deviation was within 3%.

Key words: COBALT, NICKEL, XYLENOL ORANGE, SIMULTANEOUS DETERMINATIONS, COMPLEX REACTION, RATE DIFFERENTIAL KINETICS