Implantable flow-through capillary-type microdialyzers for continuous in situ monitoring of environmentally relevant parameters.

In this paper, a simple, flexible, and cost-effective flow-through microdialyzer hyphenated with a miniaturized differential potentiometric detector is proposed for continuous diffusion-controlled sampling of analytes of environmental interest. The analytical performance of the dedicated configuration involving merely a single cellulose regenerated hollow fiber is critically compared with that of commercially available concentric probes commonly exploited for in vivo monitoring of the extracellular space in living tissues and that of large dialysis-based probes furnished with flat membranes. The outstanding feature of the capillary-type design is the ability of adapting the extraction fractions (EF) to the requirements of the assays and flow-through detectors by selection of appropriate membrane length/perfusion rate ratios. Passive sampling under steady-state conditions (EF approximately 100%) has proven feasible for environmentally relevant ions, such as chloride, by perfusing a 3-cm-long capillary with water at a flow rate of 2.0 microL/min. Hence, there is no need for recalibration of the flow setup after implantation of the purpose-made probe. The effect of physical and chemical variables on the diffusive flux is discussed in detail for the various flow-through membrane separation devices assessed. Effective means to attain identical dialysate concentrations of target species under dynamic regime irrespective of the matrix ingredients are also presented. The dedicated microdialyzer features extreme tolerance to high molecular weight interfering matrix compounds (> or =5000 mg/L humic acid) at the 5% interference level, which makes it especially suited for the interference-free potentiometric determination of ionic species in environmental samples containing high levels of organic matter. The potentials of the membrane separation unit were assessed for continuous monitoring of chemical changes in the interstitial/pore water of organic soils via stimulus-response strategies.