Two-phase liquid-liquid extraction in monosegmented flow analysis. Determination of cadmium with 1-(2ʹ-pyridylazo) naphthol

A monosegmented flow system has been developed to perform liquid-liquid extraction. Monosegmented samples are introduced in a glass tube between two air bubbles. The volume of organic phase, containing an extracting reagent, is added after the second bubble by switching on a solenoid valve using an optical sensor and a timer circuit. It was observed that the transference of the analyte from the aqueous to the organic phase is achieved by adsorption on the surface of the tube followed by desorption into the organic phase. The system was evaluated for Cd(II) extraction at pH 9.9, employing chloroform-l-(2ʹ-pyridylazo)naphthol as organic phase. The extraction efficiency is 75% and can be improved to be near 100% if the direction of the carrier flow is changed for a number of cycles in the same injection. Spectrophotometric detection 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 and a linear calibration graph was obtained for concentrations of the metal 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 employing the proposed methodology.