EXPLOITATION OF THE NITRITE CATALYTIC EFFECT TO ENHANCE THE SENSITIVITY AND SELECTIVITY OF THE ADSORPTIVE STRIPPING VOLTAMMETRIC METHOD FOR THE DETERMINATION OF COBALT WITH DIMETHYLGLYOXIME

A highly sensitive, catalytic adsorptive stripping voltammetric (AV) method for the determination of ultratrace cobalt concentrations in the supporting electrolyte consisting of ammonia buffer, dimethylglyoxime (DMG), and NaNO2 has been evaluated and compared with the well-known AV method with DMG and other dioximes. Conditions for maximal sensitivity and the simultaneous determination of Co and Ni are described. The sensitivity of the cobalt-DMG complex method is improved about 20-fold by exploitation of the catalytic effect observed in the presence of nitrite. The detection limit of the method is 4 x 10(-11) M. As a result of the selective nature of the catalytic response for cobalt, the method is more sensitive and selective against Ni and Zn than the commonly used classical DMG method (without nitrite). The method, which uses inexpensive and widely available reagents (DMG, NaNO2), is suitable for the determination of Co in the 10(-10) M-10(-9) M concentration range even when the Ni concentration is 10 to 50 times higher, as is the case in many practical situations. The method is also advantageous when the background current from sources other than Ni makes the use of the less sensitive method with DMG impossible. However, the selectivity of the method over the Ni and Zn responses is inferior than obtained with previously published but more expensive catalytic methods based on nioxime-NaNO2 or alpha-benzil dioxime-NaNO2 systems.