| Monoliths also known as "continuous beds" have rapidly become highly popular separation media after it emerged in the late 1980s, due to their simple preparation procedure, no need for retaining frits, high permeability and high surface area. Recently, monolithic materials have been applied as extraction media for sample preparation. Compared to coating fiber and open tubular capillary, monolithic column possesses more extraction sorbent and exhibits higher extraction capability. In comparison to the particle-filled column, the preparation procedure of monolithic column does not need to be packed. In addition, the monolithic porous structure facilitates convective mass transfer procedure preferable in extraction process, which helps to complete the extraction procedure within a shorter time.In tube solid-phase microextraction (in-tube SPME) is emerged as an on-line hyphenation technology of SPME and high-performance liquid chromatography (HPLC) at 1995. It not only processes the advantage of SPME such as solvent-free, rapid extraction, small sample consumption and convenient manipulation but also improves the precision of the analysis and realizes the automated manipulation. In-tube SPME meets the development trend of sample preparation:environment friendly, miniaturization and automation. Using monolith as an in-tube SPME sorbent could combine the advantages of both technologies. However, there are still several problems:(1) the type of monolith materials are not enough; (2) the in-tube SPME/HPLC system need to be improved; (3) the selectivity of polymer monolith is not high enough; (4) the hyphenation modes between in-tube SPME and HPLC are too unitary. Therefore, in order to develop sample, rapid, sensitive analytical methods and enlarge their practical application, it is worthy of preparing novel monolithic extraction media with high extraction efficiency, high selectivity and high stability and developing various combination modes between in-tube SPME and HPLC.The present work concentrates on the monolithic column and their applications to in-tube SPME-HPLC, around the preparation of novel monolithic extraction media, the design of novel combination system and the development of novel hyphenation model. The researches involved are listed below:1. The development of monolithic column technology and the application of monolithic extraction media in the field of sample preparation are reviewed.2. Octyl-functionalized hybrid silica monolithic column was synthesized by co-condensation of tetraethoxysilane (TEOS) and n-octyltriethoxysilane (C8-TEOS) via two-step acid/base-catalyzed sol-gel process. Another bifunctional hybrid monolith containing both octyl and sulfonic acid group was prepared by in-situ co-condensation of TEOS, Cg-TEOS and 3-mercaptopropyltrimethoxysilane (MPTMS) in a similar procedure followed by treating with hydrogen peroxide solution. The extraction performance and extraction mechanism of both hybrid monoliths was evaluated. In addition, they were applied to environmental and veterinary drug residues analysis, respectively.3. A fully automated in-tube SPME-HPLC system was constructed based on two six-port valves-two pumps-one autosampler system. The manipulations were detailed using analysis sulfonamide antibacterial in pure water as an example. Base on the system, a rapid, sensitive and fully automated in tube SPME/LC-MS method was developed for the analysis of ten antidepressants in human urine and plasma.4. Based on the poly(methacrylic acid-co-ethylene dimethacrylate) monolithic column, the on-line and off-line hyphenation systems of polymer monolith microextraction (PMME) and hydrophilic interaction chromatography-mass spectrometry (HILIC-MS) were developed. The combination of PMME and HILIC may be considered as an alternative to solve the problem of mismatch between desorption solution and mobile phase of RPLC. The new hyphenation systems were successfully applied to analysis of sulfonamide antibacterial residues in food andβ-agonist in human urine and animal feed. The developed methods are more rapid and sensitive, and needs relatively small volume of sample and no organic solvent for sample preparation.5. Based on the poly(methacrylic acid-co-ethylene dimethacrylate) monolithic column, an on-line hyphenation systems of PMME and LC/quadrupole time-of-flight mass spectrometry (LC/QTOF-MS) were developed. The hyphenation system was applied to determine seven trace quinolone antibacterials simultaneously in milk, egg, chicken and fish. LC/QTOF-MS offers the capability of unequivocal identification of target compounds from complex matrices, as well as the possibility of quantization at low-level concentrations in real samples. The on-line combination of PMME and LC/QTOF-MS will provide an alternative practical tool in future antibacterial residues determination as well as the monitoring of prohibited substances from complex foodstuff.6. Water-compatible pefloxacin-imprinted monoliths synthesized in a water-containing system were used for the selective extraction of fluoroquinolones (FQs). The derivated monolith showed high selectivity and was able to distinguish between FQs and quinolones. A simple rapid and sensitive method using PMME based on the MIP monolith combined with HPLC with fluorescence detection was developed for the determination of four FQs from milk samples. Owing to the unique porous structure and flow through channels in the network skeleton of the MIP monolith, phosphate buffer diluted milk samples were directly supplied to PMME; allowing non-specific bound proteins and other biological matrix to be washed out, and FQs to be selectively enriched.7. Humic acid-bonded silica was prepared and used as solid-phase extraction material for pretreatment of Sudan dyes in hot chili products, which was followed by HPLC-UV and QTOF-MS detection. The proposed method is proved to be able to remove interferences in matrices, and is simple, rapid, sensitive and robust in the regular analysis of Sudan dyes in foodstuff. |
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