2-PHASE LIQUID-LIQUID-EXTRACTION IN MONOSEGMENTED FLOW-ANALYSIS - DETERMINATION OF CADMIUM WITH 1-(2'-PYRIDYLAZO)NAPHTHOL

A monosegmented flow system has been developed to perform liquid-liqui d extraction. Monosegmented samples are introduced in a glass tube bet ween two air bubbles. The volume of organic phase, containing an extra cting reagent, is added after the second bubble by switching on a sole noid valve using an optical sensor and a timer circuit. It was observe d that the transference of the analyte from the aqueous to the organic phase is achieved by adsorption on the surface of the tube followed b y desorption into the organic phase. The system was evaluated for Cd(I I) extraction at pH 9.9, employing chloroform-1-(2'-pyridylazo)naphtho l as organic phase. The extraction efficiency is 75% and can be improv ed to be near 100% if the direction of the carrier flow is changed for a number of cycles in the same injection. Spectrophotometric detectio n was made without phase isolation at the end of the extraction tube. The detection limit (signal-to-blank = 3) for Cd(II) is 85 ng l(-1) an d a linear calibration graph was obtained for concentrations of the me tal up to 2.0 mg l(-1). Samples can be introduced in the system at 30 h(-1). Other metals such as Cu(II) and Zn(II) can be also extracted em ploying the proposed methodology.