In-situ Dispersive Liquid-liquid Microextraction And Its Application In Gas Chromatography

The concept of ‘Green Analytical Chemistry'(GAC) was proposed in 1999, the core of which is to decrease or eliminate the use and generation of toxic reagents by analytical technology. In this context, the sample preparation is evolved into microextraction of reduced or eliminated reagents, including solid-phase microextraction(SPME) and liquid-phase microextraction(LPME), from solid-phase extraction and liquid-liquid extraction. As a novel sample preparation technique of LPME, dispersive liquid-liquid microextraction(DLLME) has obtained considerable attention from analytical chemical researchers, due to its distinct merits of excellent green chemical indices and enrichment factors in the magnitude of several hundreds. More than 1000 scientific articles related to the DLLME technique were published, including some reviews on the topic of DLLME.The crucial step in DLLME is to completely disperse the extraction solvent at micro-liter level in the aqueous sample solution. The strategies of dispersion in DLLME are roughly classified into three types in terms of the instruments used and dispersion principles, namely devices assisted dispersion method, in-situ chemical reaction-based dispersion method and new dispersion medium-based dispersion method. The master's work is based on in-situ chemical reaction-based dispersion method, in which the dispersive devices in devices assisted dispersion method and special mediums in new dispersion medium-based dispersion method are no more important. This paper is divided into three chapters shown as follow.Chapter 1: Introduction. A key introduction of progress of extraction solvent dispersion strategies for DLLME was presented. The published strategies of dispersion for DLLME are roughly classified into three types in terms of the instruments used and dispersion principles, namely devices assisted dispersion method, in-situ chemical reaction-based dispersion method and new dispersion medium-based dispersion method. The devices assisted dispersion method includes vortex, up-and-down-shaker, magnetic stirring, and ultrasound/microwave-assisted method. The in-situ chemical reaction method is referred to the two modes, in which either the dispersed extraction solvent is formed by an in-situ chemical reaction or the dispersion of extraction solvent is achieved by the gas generated from chemical reactions. The new dispersion medium-based dispersion method uses some non-volatile substances, such as medium-chain saturated fatty acids, ionic liquid and surfactant, to substitute the dispersive solvent used in conventional DLLME.Chapter 2: A novel effervescence-assisted dispersive liquid–liquid microextraction(EA-DLLME) technology was developed. In this technology, the citric acid aqueous solution and extraction solvent are effectively mixed by manual shaking and then slowly injected into previously prepared sample solution containing potassium carbonate at the bottom of the extraction vial. The carbon dioxide generated from in-situ reaction emits in the form of effervescence and the extraction solvent is homogeneously dispersed in sample solution from bottom to top. A good dispersion efficiency can be achieved by a simple, green and fast in-situ effervescence reaction without help of assisted devices and dispersive mediums. The extraction time is only 30 s. After centrifugation, the sedimented phase enriched with target analytes is analyzed by gas chromatography-flame ionization detection(GC-FID).Chapter 3: In this paper, a novel sample pre-treatment method, a green deep eutectic solvents(DESs)-based back extraction, is proposed to improve the adaptation of in-situ dispersion method for complex samples and edible oil in daily life is chosen as analytic target. The extraction process can be classified into two steps:(i) Forward extraction. The target analytes are extracted into DESs based on the theory of “like dissolves like”. Due to the green properties similar with ionic liquids, substituting DESs for the organic solvents in conventional oil extraction is more in line with the development needs of GAC.(ii) Back extraction(in-situ DLLME). The sedimented phase of DESs, from forward extraction, is dissolved in a certain amount of deionized water. The target analytes are released into aqueous phase, extracted into chloroform phase produced from the in-situ reaction of chloral hydrate and sodium hydroxide at room temperature and then injected into GC-FID to analyze. This step can clean up the sedimented phase of DESs, not just making it possible to analyze real oil samples, but also addressing the issue of compatibility of DESs with direct GC detection.