Abstract: A new, simple and low-cost flow injection system with two solid-phase reactors and spectrophotometric detection for speciation of Cr(III) and Cr(VI) has been proposed. A polyethylene mini-column (60 mm and 0.7 mm i.d.) filled with 1,5-diphenylcarbazide (25% m/m suspended on silica gel beads) in below, 1,5-diphenylcarbazone (25% m/m suspended on silica gel beads) in middle and Jones-reductor in up (reactor I), and another column filled only with 1,5-diphenylcarbazide (reactor II) were incorporated into a flow system. In reactor I, Cr(III) in samples (containing both Cr(III) and Cr(VI)) injected into 0.5 M H2SO4 as a carrier stream was reduced to Cr(II) by Jones-reductor, which was determined spectrophotometry at 548 nm by complexation with 1,5-diphenylcarbazone. Also, Cr(VI) was determined after complexation with 1,5-diphenylcarbazide in reactors I and II in the same wavelength. The amount of Cr(III) in the sample was estimated as the difference in the two determination from reactor I and reactor II. The calibration plots were up to 30 ?g mL-1 and 35 ?g mL-1 for Cr(III) and Cr(VI), respectively. Detection limits (3?) were 70 ?g L-1 for Cr(III) and 30 ?g L-1 for Cr(VI) with a relative standard deviation <1.7%. The proposed system is suitable for determination of Cr(III), Cr(VI) and total chromium in spiked and effluent streams samples.

Abstract: A new rapid and sensitive flow injection analysis method for determination of ascorbic acid in pure form and in a number of their pharmaceutical preparations and real samples is proposed. The method is based on the oxidation of ascorbic acid by a known excess amount of potassium chromate followed by the estimation of unreacted amount of chromate by reacting with dissolution sym-diphenylcarbazide. Solid sym-diphenylcarbazide (35% m/m suspended on silica gel beads) is packed in a steeliness column, which is then incorporated in a single-line flow system so that reagent dissolution is affected as the remaining chromate ions passes through the column. The reacted oxidant corresponds to the ascorbic content. At the maximum absorption of 548 nm, the calibration curve was linear up to 12 ?g mL-1 of ascorbic acid with a detection limit of 0.05 ?g/ml, RSD of better than 1.65% and sampling frequency of 90 h-1. Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedure. The reliability of the method was established by parallel determination against the 2,6-dichorophenolindophenol methods. The procedure described was successfully applied to the determination of the bulk drugs, in pharmaceutical formulations and real samples.

Abstract: 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-diphenylcarbazone 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 H2SO4 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 ?g mL-1 of chromium species with a 3? detection limit of 0.09 ?g L-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.