AN AUTOMATED-SYSTEM FOR LIQUID-LIQUID-EXTRACTION IN MONOSEGMENTED FLOW-ANALYSIS

An automated system to perform liquid-liquid extraction in monosegment ed flow analysis is described. The system is controlled by a microcomp uter that can track the localization of the aqueous monosegmented samp le in the manifold. Optical switches are employed to sense the gas-liq uid interface of the air bubbles that define the monosegment. The logi cal level changes, generated by the switches, are flagged by the compu ter through a home-made interface that also contains the analogue-to-d igital converter for signal acquisition. The sequence of operations, n ecessary for a single extraction of for concentration of the analyte i n the organic phase, is triggered by these logical transitions. The sy stem was evaluated for extraction of Cd(II), Cu(II) and Zn(II) and con centration of Cd(II) from aqueous solutions at PH 9.9 (NH3/NH4Cl buffe r) into chloroform containing PAN (1-(2-pyridylazo)-2-naphthol). The r esults show a mean repeatability of 3% (rsd) for a 2.0 mg l(-1) Cd(II) solution and a linear increase of the concentration factor for a 0.5 mg l(-1) Cd(II) solution observed for up to nine extraction cycles.