Metal speciation by flow-injection analysis.

A two-channel switching valve is incorporated in the flow-injection manifold for on-line control of the metal speciation of Fe(II)/Fe(III) and Cr(III)/Cr(VI). 1,10-Phenanthroline is used for the iron determinations and diphenylcarbazide for chromium. The absorbances are measured at 512 and 540 nm, respectively. When a 30-mul injection loop is used, the response is linear for 0.5-30.0 ppm Fe and 0.5-40.0 ppm Cr. The relative standard deviation in each case is approximately 1%. The method allows at least 180 injections per hour.