Miniaturized, Membrane-Based and Environmentally Green Sample Preparation Systems: Applications for Biological and Environmental Aqueous Samples
Sammanfattning: Contemporary advancements in miniaturization of analytical systems have advantageously fostered development, automation, and hyphenation of a variety of sample preparation techniques. Among several downscaled extraction designs, porous synthetic polymeric membranes (such as flat sheet (FS) or hollow fiber (HF)) have been utilized for membrane-based extraction, separating two aqueous phases (as in supported liquid membrane (SLM) extraction or one aqueous phase and another organic phase (as in microporous membrane liquid-liquid extraction (MMLLE)). The SLM and MMLLE configurations permit usage of microliter-volumes of extraction solvent, and therefore, are considered to be environmentally friendly. This dissertation addresses miniaturized membrane-based extraction techniques that were operated in automated, flowing, and on-line fashion as well as in nonautomated, nonflowing, and off-line setups. These environmentally green systems based on SLM and MMLLE were appraised for trace extraction of organic compounds (such as basic and acidic pharmaceuticals (by SLM), and PCBs, OCPs, and PBDEs (by MMLLE)) in environmental and biological aqueous samples. Exhaustive extraction and non-depletive equilibrium extraction exhibiting high level of analyte preconcentration were demonstrated. The former was performed for total analyte recovery. The later was pursued so as to quantify free analyte concentration in a sample containing an analyte and a binding phase, such as a protein or humic acids. For instance, by measuring the free drug concentration, the level of drug-protein binding (DPB) was quantitatively estimated as well as the DPB process was characterized and interpreted by obtaining the binding parameters from Scatchard and Bjerrum plots. The results revealed that, although the flowing on-line systems exhibited excellent performance (e.g. the Extracting Syringe device permitting a full automation of a µMMLLE with an on-line hyphenation to gas chromatography in a closed system and limits of detection at very low ng L-1 concentration level), the flowing systems suffered from setup complexity, low extraction efficiency, and problems with analyte carryover and adsorption. By contrast, the nonautomated nonflowing designs allowed simplified and easy-to-use procedures, high analyte extraction efficiency and enrichment, and no carryover and no adsorption problems as the HF-SLM or HF-MMLLE device was employed for only a single use. In conclusion, the HF-based, nonautomated, and nonflowing setups of SLM and MMLLE have been shown to have attractive merits when employed for exhaustive as well as non-depletive equilibrium sampling. The latter design has strong potential applications for speciation of freely dissolved organic compounds, and a promising development is expected in its application for environmental and biological samples.
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