Membrane optode for uranium(VI) ions preconcentration and quantification based on a synergistic combination of 4-(2-thiazolylazo)-resorcinol with 8-hydroxyquinaldine.

A membrane optode was developed utilizing the 8-hydroxyquinaldine (HQ) facilitated preconcentration of UO(2)(2+) ions and subsequent colored complex formation of UO(2)(2+) with 4-(2-thiazolylazo)-resorcinol (TAR) in optode matrix. The composition of the membrane optode was optimized by scanning several extractants immobilized in different plasticized polymer matrices. It was observed that the chelating agent HQ along with an indicator TAR immobilized in the tri-(2-ethylhexyl)phosphate (TEHP) plasticized cellulose triacetate matrix (CTA) was best suited as an optode for the UO(2)(2+) ions in aqueous samples. On sorption of UO(2)(2+) in the optode matrix, TAR changes color of the optode from yellow to magenta having a maximum absorbance (lambda(max)) at 546 nm. The uptake of UO(2)(2+) ions in the optode was found to be pH dependent and was maximum (>90%) at pH above 3. The acetate buffer (0.1 mol L(-1) sodium acetate + 0.1 mol L(-1) acetic acid) was found to be necessary for the stable response. The optimum equilibration time for the optode (2 cm x 1 cm) was found to be 30 min in 10 mL aqueous sample containing acetate buffer (pH 4.75). The equilibration time was found to increase with increase in aqueous sample volume. The optode response was found to be linear in the UO(2)(2+) ions concentration range of 0.01-0.11 micromol L(-1) in tap water as well as aqueous solutions containing 0.1 mol L(-1) NaCl or NaNO(3). The tolerance to the presence of several cations and anions in the determination of UO(2)(2+) ion was studied. It was observed that the optode in the presence of buffer can tolerate presence of large amounts of interfering cations (Ce(4+), V(4+), Eu(3+), Al(3+), Fe(3+), Ni(2+), Cd(2+), Co(2+), Pb(2+), Hg(2+), Cu(2+) and Th(4+) ions) without hindering the sorption of UO(2)(2+) ions in the optode matrix. The present work indicated that 50 ppb UO(2)(2+) ions in 100 mL sample can easily be quantified using this optode. The optode was found to be fully reversible, can readily be regenerated by equilibrating it with 0.1 mol L(-1) HNO(3) and reusable up to three cycles. The applicability of the developed optode in real samples was studied by determining uranium in the ground water samples spiked with a known quantity of UO(2)(2+) ions.