Solid reactors in sequential injection analysis: Recent trends in the environmental field

The second generation of flow injection analysis (FIA), so-called sequential injection (SI), has already been consolidated as an attractive flowing-stream approach in several analytical fields, with advantages over the first generation of FIA in terms of automation, miniaturization, and sample/reagent consumption. A further noteworthy feature is the inherent versatility of the flow network to implement unit operations at will with no need for manifold re-configuration. The present review discusses the potential of SI to accommodate solid reactors and packed columns in the flow set-up for environmental applications, aiming to facilitate on-line chemical derivatization, chromatographic separation of target species, removal of interfering matrix compounds, or determination of trace levels of analyte via sorptive preconcentration procedures. In this context, the concept of renewable surfaces, so-called SI-bead injection (SI-BI), used in either the jet-ring or lab-on-valve configurations, is presented as a front-end to many detectors. This article also outlines recent trends focused on exploiting SI as an automated tool for handling solid samples of environmental concern and accommodating dynamic fractionation schemes for trace elements.