A new approach for compensating concentration gradients in flow analysis

A novel strategy for compensating gradient concentrations in flow analysis is proposed. It is based on the establishment of similar and opposite 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. Elution is accomplished by replacing an acidic 8.0 M LiCl by a 0.5 M NaNO3 stream, promoting partial mixing between them, and allowing the mixing boundary to pass through the resin minicolumn. The gradual reduction of the chloride concentration promotes sequential elution in view of the different stability constants of the retained chlorocomplexes. The eluted metal ions then react with Zincon and are spectrophotometrically monitored. Potentialities and limitations of the approach are discussed.