FIA-coupled spectrophotometric method for determination of Cr (VI) traces in natural waters: application of in-line dissolution of 1,5-diphenylcarbazide after heat treatment and activated alumina as adsorbent for preconcentration.

This work proposes the quantification of Cr (VI) ions in natural waters in trace level, using activated alumina (Al2O3) as preconcentration support, controlled in-line dissolution of the solidified chromophore diphenylcarbazide after heat treatment and spectrophotometric detection. The manifold ensures high sensitivity of analytical response, good repeatability, and stability. In this work, optimization of experimental conditions of a flow injection system was chosen as the parameters for greater sensitivity and better selectivity. The selected optimized conditions were 0.30 mol L-1 for H2SO4 concentration, system flow rate as 0.40 mL min-1, sample injection volume of 192.50 µL, 2 min for preconcentration time, and 0.10 mol L-1 for eluent concentration. The analytical curves obtained for real sample analysis show linear range from 0.192 to 0.961 µM, linear correlation coefficient R = 0.9997 and LOD = 0.024 µM. The preconcentration factor of about four times was obtained through the passage of 800 µL of a standard solution containing 0.961 µM of Cr (VI) through mini-column of preconcentration followed by elution at 192.5 µL of NH4OH 0.1 mol L-1 solution. The solid chromogenic reagent presented high durability (weeks in daily use with mass of 0.0993 g) and good reproducibility in analytical signal. The reactivation of the mini-column of alumina should be executed after ten injections of eluent, using 800 µL of HCl 0.02 mol L-1 solution in flow through the same. Each cycle of injection and elution of the sample takes about 5 min on the proposed terms. Despite the length of each cycle still be high, low concentrations can be detected using a technique of relatively low cost. This is due in part, the association dissolution of the chromogenic reagent directly in the line and the preconcentration step. Another important factor is the economy of reagent chromogenic, low generation of reject contributing to better quality of the environment, and the high potential for applications to work in field.

Cr(VI) and Cr(VI)-diphenylcarbazide removal from aqueous solutions using an iron rotating disc electrode.

This paper presents the results of the investigation on the removal of Cr(VI) and the complex Cr(VI)-diphenylcarbazide from aqueous solutions using an electrochemical reactor, with iron electrodes. A maximum value of 99% Cr(VI) removal from aqueous solutions is observed for both Cr(VI) and Cr(VI)-diphenylcarbazide, at initial concentrations from 150 to 800 mg l(-1). Cyclic voltammetry experiments of water show the presence of electroactive species in the oxidation and reduction zones previous to the treatment and how this presence diminishes as the electrochemical treatment is applied to the wastewater. UV-Vis analyses corroborate the improvement on the quality of aqueous solutions treated. Finally, scanning electron microscopy and energy dispersion spectra show that Cr and Fe are present as constituents of the sludge formed during the electrochemical treatment. It was demonstrated that the use of electrochemical methods for the treatment of Cr(VI) and Cr(VI)-diphenylcarbazide aqueous solutions is an effective and economical method.

Chromium(III) determination with 1,5-diphenylcarbazide based on the oxidative effect of chlorine radicals generated from CCl4 sonolysis in aqueous solution.

Oxidation of Cr(III) during sonication in carbonated aqueous solutions saturated with CCl4 leads to the quantitative formation of Cr(VI) and provides a simple and rapid method for spectrophotometric chromium determination with 1,5-diphenylcarbazide. The key to this method is the production of chlorine radicals when aqueous solution saturated with CCl4 is exposed to ultrasonic waves of 40 kHz. The effects of sonication period, CCl4 solution volume, acidity, and interferences were discussed. The time required for a single determination is lower than 2 min. The relative standard deviation obtained for aqueous solutions with 1 microg of Cr was < 2% (N = 10) and the calculated detection limit (3sigma) was 5 ng of Cr.