Analytical Sciences

Abstract − Analytical Sciences, 21(6), 673 (2005).

A Potentiometric Rhodamine-B Based Membrane Sensor for the Selective Determination of Chromium Ions in Wastewater
Saad S. M. HASSAN,* M. S. EL-SHAHAWI,** A. M. OTHMAN,*** and M. A. MOSAAD**
*Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt
**Chemistry Department, Faculty of Science at Damiatta, Mansoura University, Egypt
***Genetic Engineering and Biotechnology Research Institute (GEBRI), Minufiya University, Sadat City, Egypt
The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used for determining chromium(III) and chromium(VI) ions. The sensor is based on the use of a rhodamine-B chromate ion-associate complex as an electroactive material in a poly(vinyl chloride) membrane plasticized with o-nitrophenyloctyl ether as a solvent mediator. In a phosphate buffer solution of pH 6 - 7, the sensor displays a stable, reproducible and linear potential response over the concentration range of 1 × 10-1 - 5 × 10-6 mol l-1 with an anionic Nernstian slope of 30.8 ± 0.5 mV decade-1 and a detection limit of 1 × 10-6 mol l-1 Cr(VI). High selectivity for Cr(VI) is offered over many common anions (e.g., I-, Br-, Cl-, IO4-, CN-, acetate, oxalate, citrate, sulfate, phosphate, thiosulfate, selenite, nitrate) and cations (e.g., Ag+, Ca2+, Sr2+, Co2+, Ni2+, Cu2+, Mn2+, Fe2+, Zn2+, Cd2+, Al3+, Cr3+). The sensor is used for determining Cr(VI) and/or Cr(III) ions in separate or mixed solutions after the oxidation of Cr(III) into Cr(VI) with H2O2. As low as 0.2 µg ml-1 of chromium is determined with a precision of ±1.2%. The chromium contents of some wastewater samples were accurately assessed, and the results agreed fairly well with data obtained by atomic absorption spectrometry.