A NEW APPROACH FOR COMPENSATING CONCENTRATION GRADIENTS IN FLOW-ANALYSIS

A novel strategy for compensating gradient concentrations in flow anal ysis is proposed. It is based on the establishment of similar and oppo site gradients in a symmetric confluent stream. As an application, the spectrophotometric determination of nickel, cobalt and zinc involving sequential elution of their anionic chlorocomplexes from a Dowex AG1- X8 resin (200-400 mesh, chloride form) minicolumn is described. Elutio n is accomplished by replacing an acidic 8.0 M LiCl by a 0.5 M NaNO3 s tream, promoting partial mixing between them, and allowing tile mixing boundary to pass through the resin minicolumn. The gradual reduction of the chloride concentration promotes sequential elution in view of t he different stability constants of the retained chlorocomplexes. The eluted metalions then react with Zincon and are spectrophotometrically monitored. Potentialities and limitations of the approach are discuss ed.