Recent advances in on-line solvent extraction exploiting flow injection/sequential injection analysis

In this paper, the state-of-the-art of automated solvent extraction procedures exploiting flowing stream techniques is thoroughly presented and discussed. While flow-injection liquid-liquid extraction (FI-LLE) was originally associated with the use of a solvent extractor involving a segmentor and a phase separator, current analytical trends are focused on the design and characterisation of novel strategies for the removal of the classical instrumentation aimed at improving the efficiency of phase separation as well as the repeatability, sensitivity and accuracy of the analytical chemical assays. Salient alternatives implemented in flow systems for on-line sample processing and detection of the analytes in the phase of interest, based on the principles of on-tube detection, membrane-assisted LLE, iterative forward-backward flow, cloud-point extraction, static-phase separation, single-drop solvent extraction, and chromatomembrane separations, amongst others, are critically compared in terms of analytical performance, instrumental set-up and potential applications. Special emphasis is given in the bulk of the text to the inherent capability of sequential injection (ST) analysis to accommodate the new concept of renewable phase extraction in open tubular reactors, so-called wetting-film extraction (WFE), which is performed in the conduits of the SI assembly without the need for any ancillary hardware, thereby minimizing the risks of sample carryover. Its fundamental background, critical experimental variables, hyphenation with flow-through detectors, and analytical figures of merit are thoroughly discussed and exemplified with selected applications in the environmental and clinical field.