Flow injection spectrophotometric determination of chromium(VI) after preconcentration on potassium-benzoic acid hydrazide dithiocarbamate

In this study a sensitive, easy to operate, robust and reproducible column preconcentration method was developed for the determination of Cr(VI) by flow injection system coupled with spectropho-tometer. The proposed method is based on the retention of the analyte in a column containing potassium-benzoic acid hydrazide dithiocarbamate from buffered solution of pH 4.0 at a flow rate of 15 mL center dot min-1, and then its elution from the column with 7.0 mol center dot dm-3 nitric acid solution. The eluted Cr(VI) solution was then mixed with 0.25% solution of 1,5-diphenylcarbazide (DPC) and pur-ple-red Cr(VI)-DPC complex was determined spectrophotometrically at 545 nm in acidic medium. The parameters studied include volume, pH, flow rate and concentration of the sample solution, different eluents and their concentration. The proposed method has a linear calibration range from 3-15 mg center dot L-1 of Cr(VI) with the regression y = 0.0467C + 0.0013, R2 = 0.9984. The 3 delta detection limit of Cr(VI) is 1 mu g center dot L-1 with enrichment factor of 4, sampling frequency of 6 samples center dot h-1 and relative standard deviation of 1.82% at 10 mg center dot L-1. The adsorbent used has a good adsorption potential as well as appreciable recovery. The column had a constant performance during all experiments except 2%-3% loss during flow rate optimization. The developed method was effectively employed for the determination of Cr(VI) from standard reference material (CRM Cu1/3 Cu alloy).