Mn(III)-diphenylcarbazone immobilized on silica gel as an oxidant for speciation of chromium(III) and chromium(VI) in a flow injection system

A flow injection analysis method comprising two solid-phase reactors and spectrophotometry for speciation of Cr(III) and Cr(VI) is reported. A polyethylene mini-column half filled with 1,5-diphenylcarbazide (suspended on silica gel beads) and half filled with Mn(III)-1,5-diphenylcarbazone (immobilized on silica gel beads), reactor 1, and another column filled only with 1,5-diphenylcarbazide (suspended on silica gel beads). reactor 2, which are then incorporated in a flow system so that Mn(III)-1,5-diphenyicarbazone and 1,5-diphenylcarbazide reagents in reactors are affected as the sample passes through the columns. In reactor 1, Cr(III) in samples (containing both Cr(III) and Cr(VI)) injected into 0.5 M H 2 so 4 as a carrier stream was oxidized by Mn(III)-1,5-diphenylcarbazone to form Cr(VI), then total Cr(VI) was detected by spectrophotometry at 548 nm by complexation with 1,5-diphenycarbazide. Chromium (VI) in samples is determined after injection through reactor 2; the difference in the two analytical signals observed is related to amount of chromium(III). The calibration curve was linear up to 3.0 mug ml(-1) of chromium species with a 3 mu detection, limit of 0.09 mug 1(-1) and a relative standard deviation <1.34%. The method is free from most interferences. The proposed system is suitable for determination of Cr(III) and Cr(VI) and total chromium in spiked and effluent streams samples.