Abstract

The on-line incorporation of cloud point extraction (CPE) into flow injection analysis (FIA) associated with ICP-OES for determining metal ions is presented and evaluated. The methodology is based on the complexation of Gd(III) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in the presence of non-ionic micelles of PONPE-7.5. The micellar system containing the complex was thermostated at 25 °C and loaded into the FIA manifold at a flow rate of 5 ml min⁻¹, and the surfactant rich-phase was retained in a micro-column packed with cotton, at pH 9.2. The surfactant-rich phase was eluted with 4 mol l⁻¹ nitric acid at a flow rate of 1.5 ml min⁻¹ directly into the nebulizer of the plasma. An enhancement factor of 20 was obtained for the preconcentration of 10 ml of sample solution. The detection limit for the preconcentration of 10 ml of aqueous solution of Gd was 40 ng l⁻¹. The precision (RSD) for 10 replicate determinations at the 2.0 µg l⁻¹ Gd level was 1.9%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for gadolinium was linear, with a correlation coefficient of 0.9997 at levels near the detection limit up to at least 50 µg l⁻¹. The method was successfully applied to the determination of gadolinium in urine.