Flow system for liquid–solid extraction and pre-concentration using a renewable extracting solid phase Original Research Article

A mechanised flow system is described aimed at extracting and pre-concentrating metal ions in a renewable water-insoluble solid phase containing a suitable ligand. The main difference between the proposed system and previously described ones for use with liquid–solid extraction is in the renewable characteristics of the solid phase, which allows for refreshing the extracting surface to be employed between pre-concentration operations. The renewable feature imposes no demands in terms of reversibility of the adsorption process as all the solid organic phase containing the complexed metal is dissolved by a non-aqueous solvent and carried to the detection system. Simultaneously, the system promotes a better compromise between metal extraction and pre-concentration as lower solvent volumes can be used to recover the absorbed species. The system has been evaluated for Zn(II) extraction in order to optimise its main geometrical and chemical variables. A simple spectrophotometric detection system employing a light emitting diode (LED) and a silicon photodiode was employed in these studies. Concentration gains of 42 and detection limits below 1.0 μg l−1 were obtained. Sample throughput and sample consume depend on the desired pre-concentration. For higher (>40) concentration factors, about 40 ml of aqueous sample and a total processing time of 20 min per sample are required.