Miniaturized extraction and separation media have been successfully developed from precisely controlled technologies. In this article, recent developments in these high performance analytical methods, such as miniaturized sample preparation methods and the coupling of these techniques with microscale separation systems, have been reviewed, along with some applications to environmental and biological analysis. The advantage of the miniaturization is not only for the environmental compatibility but also for the developments of the high performance analytical systems. Down-sizing also makes it possible to investigate and introduce various compounds and materials as novel media (such as tailor-made materials and devices) in separation science. As a typical example of the novel miniaturized sample preparation system, the applications of fibrous materials for microcolumn liquid-phase separation methods are described.
Miniaturized solid-phase extraction (SPE) has been developed and successfully employed for the determination of organic species in water samples by liquid chromatography (LC). The method is based on the concept of a microscale extraction technique using a fused-silica capillary column for gas chromatography (GC), so-called in-tube solid-phase microextraction (SPME). The extraction conditions, such as the extraction time and flow-rate for the extraction and desorption process, were investigated as well as the effect of the internal structure of the extraction capillary on the efficiency. By inserting a stainless steel wire into the extraction capillary to reduce the internal volume of the capillary with the same surface area of the coating, an improved extraction and pre-concentration effects were obtained. Further pre-concentration was accomplished by the extraction device with a novel fiber-in-tube configuration. The direct coupling of the extraction method with a LC system has made it possible to determine low levels of phthalates in water samples without high consumption of organic solvents. The system developed must have potential applications for the analysis of environmental and biological samples in aqueous sample matrices.
On-line coupling of fiber-in-tube solid-phase extraction (SPE), using poJyetheretherketone (PEEK) tubing, with microscale liquid chromatography (LC) has been investigated. PEEK tubing and polymer filaments are introduced as new medium for extraction of phthalates -diethyl phthalate (DEP), dipropyl phthalate (DPP), and dibutyl phthalate (DBP). Approximately 300 pieces of polymer filamentwere packed into a PEEK capillary 100 mm long (0.25 mm i.d.) and the capillarywas installed in the injection valve as the sample loop. Desorption and injection of the analytes were performed simultaneouslywithout use of the desorption solvent required by conventional SPE methods.The results obtained showed that effective on-line coupling of this sample-preparation method with liquid chromatography and other liquid-phase separation techniques can be accomplished for the high-throughput analysis of complex mixtures, without large consumption of organic solvents. The limits of detection for these phthalates, approximately 1.0 ng mL 1, and the extraction time, 10 min, indicate the future possibilities of this technique.
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