Flow dissolution of 1,5-diphenylcarbazide for the determination of chromium(VI)

An alternative procedure for the flow injection spectrophotometric determination of Cr-VI with 1,5-diphenglcarbazide (DPC), involving on-line dissolution of the reagent, is presented. Solid DPC (25% m/m in silica) is packed in a PTFE column, which is then incorporated in a single-line flow system so that reagent dissolution is effected as the sample passes through the column, This procedure reduces the chemical contribution to the dispersion value to a minimum and gives a low detection limit owing to the absence of refractive index peaks. An improvement of the figures of merit compared with those reported previously is shown, The calibration graph is linear up to 0.800 mg l(-1) Cr-VI, with a slope of 0.49 l mg(-1); the detection limit is 0.005 mg l(-1), The relative standard deviation is better than 1%.