Solvent bar microextraction

Y., and Lin, J.-M. (2012) A vortex solvent bar microextraction combined with gas chromatography-mass spectrometry for the determination of phthalate esters in various sample matrices. Talanta, 100, 64-70. 

Miniaturisation of scientific instruments, following on from size reduction of electronic devices, has recently been hyped up in analytical chemistry (Tables 10.19 and 10.20). Typical examples of miniaturisation in sample preparation techniques are micro liquid-liquid extraction (in-vial extraction), ambient static headspace and disc cartridge SPE, solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE). A main driving force for miniaturisation is the possibility to use MS detection. Also, standard laboratory instrumentation such as GC, HPLC [88] and MS is being miniaturised. Miniaturisation of the LC system is compulsory, because the pressure to decrease solvent usage continues. Quite obviously, compact detectors, such as ECD, LIF, UV (and preferably also MS), are welcome. 

Besides classical headspace analysis, simultaneous distillation-extraction and solvent extraction, new sampling and enrichment developments include solvent-assisted flavour evaporation (SAFE) [3] and sorptive techniques like SPME solid-phase microextraction (SPME) [4,5] and stir-bar sorptive extraction (SBSE) [6], which are treated in a dedicated chapter in this book. This contribution will deal with advanced developments of GC techniques for improvement of separation and identification (classical multidimensional GC, or... 

The extraction techniques described in this book fulfill many of Anastas and Warner s principles. For example, the use of supercritical carbon dioxide (SC-CO2) as the sole extraction solvent results in a nonpolluting process (prevention of waste and safer solvents and auxiliaries). Other beneficial properties of supercritical CO2 include fast diffusivity and nearly zero surface tension, which lead to extremely efficient extractions. In Chapters 2-4, applications of SC-CO2 as an extraction solvent are described. Ethanol and water are also environmentally friendly solvents that can be used as extraction media in many applications (see Chapters 5-7). Pressurized hot water ( 100-200 °C) in particular is a safe and nonpolluting solvent that has a similar dielectric constant to polar organic solvents, such as ethanol or acetone. Hence, pressurized hot water is a viable green alternative to many current extraction processes that use toxic organic solvents. Similarly, pressurized hot ethanol is an excellent solvent for the extraction of most medium polar to nonpolar organic molecules. Some of the techniques, such as membrane-assisted solvent extraction, described in Chapter 10, use organic solvents but in much smaller amounts compared to classical extraction techniques. Other techniques, for instance solid-phase microextraction and stir-bar sorptive extraction, described in Chapter 11, use no solvents. 

The search of adequate extraction techniques allowing the identification and quantification of wine volatile compounds has attracted the attention of many scientists. This has resulted in the availability of a wide range of analytical tools for the extraction of these compounds from wine. These methodologies are mainly based on the solubility of the compounds in organic solvents (liquid-liquid extraction LLE, simultaneous distillation liquid extraction SDE), on their volatility (static and dynamic headspace techniques), or based on their sorptive/adsorptive capacity on polymeric phases (solid phase extraction SPE, solid phase microextraction SPME, stir bar sorptive extraction SBSE). In addition, volatile compounds can be extracted by methods based on combinations of some of these properties (headspace solid phase microextraction HS-SPME, solid phase dynamic extraction SPDE). 

Accelerated solvent extraction (ASE), focused microwave soxhiet extraction (FMSE), immuno affinity cleanup (im-Cu), liquid-liquid extraction (LLE), low-temperature lipid precipitation (LTLP), matrix solid-phase dispersion (MSPD), microwave-assisted extraction (MAE), nanofiltration (NF), pressurized fluid extraction (PEE), single drop microextraction (SOME), solid-phase extraction (SPE), solid-phase microextraction (SPME), steam distillation (SD), stir bar sorptive extraction (SBSE), surpercritical fluid extraction (SFE), subcritical fluid extraction (ScFE), supported liquid membrane extraction (SLME), ultra-sonication (US), size exclusion chromatography (SEC), liquid chromatography-fraction collection (LC)... 

Aerosols are collected with filters made of glass fibres, with pores up to 5 p.m, and next dissolved in a proper solvent or solvent mixture. Chemical warfare agents or their degradation products, which are dissolved in water or other solvents, are extracted by hquid-liquid extraction (LLE), sohd-phase extraction (SPE), sohd-phase microextraction (SPME), and stirr bar sorptive extraction (SBSE) methods. Head space (HS) analysis is also employed. In the case of the SPE method, XAD-4 and XAD-2 resins are frequently used. 

The nature of flavor compounds creates challenges for analysis. Aroma compounds must be volatile. They are usually present at very low concentrations in foods. Despite the fact that hundreds of volatile compounds are often present in a food, only a few may be odor-active. Gas chromatography has been an invaluable tool for separation and subsequent identification of volatile compounds. Concentration of flavor chemicals is often necessary since the compounds are usually present at low levels. Some methods of sample preparation are described in this handbook, including solid-phase microextraction (see Chapters 16, 20-22, 30, and 31), sorptive stir bar extraction (Chapter 32), absorption on a porous polymer (Chapters 21, 22, and 27), super-critical CO2 extraction (Chapter 22), simultaneous steam distillation (Chapter 31), accelerated solvent extraction (Chapter 35), simultaneous distillation extraction (Chapters 21 and 31), and direct gas injection with cryofocusing (Chapter 20). Sampling conditions are considered in Chapters 20, 23, and 24, and comparisons of some chemical detector sensitivities are made in Chapters 18, 23, and 27-29. 

Today, sample preparation is maybe the step that most influences the accuracy of the whole analytic method, with the extraction of pesticide residues from environmental matrices the key factor for achieving it. There is no question that in the first decade of the century, SPE technique [72] is the most employed alternative to the classical solid-liquid [13] and liquid-liquid [14] extractions. These classical techniques present multiple disadvantages such as the low recovery of polar pesticides and transformation products (in the case of liquid-liquid extractions) and use of large volumes of solvents. Furthermore, several variants emerged based on the SPE technique solid-phase microextraction (SPME) [72-74], in-tube solid-phase microextraction [72,75,76], matrix solid-phase dispersion [72,77,78], and stir-bar sorptive extraction [72,79]. 

To date, many analytical procedmes have been developed for the analysis of PAHs in water, soil, air and food matrices, most of them using LC or gas chromatography (GC). The conventional approach for the analysis of these pollutants in water samples involves the previous preconcentration of the analytes by liquid-liquid extraction (LLE) or SPE, often combined with solvent evaporation [2-8], Recent research efforts are oriented towards the development of simplified and miniaturized sample treatment methods which reduce the time of analysis, the consumption of chemicals and the generation of wastes. In this respect, different alternatives have been proposed for PAHs based on the miniaturization of LLE [9, 10] or SPE [11, 12], but the most popular approach is solid-phase microextraction (SPME). SPME permits the detection and quantification of PAHs at low to sub ppb levels using for analyte enrichment either fibres [13-18] or stir bars [19, 20] coated with an extractive phase. The long adsorption times required to extract the analytes, up to several hours in some of the reported assays [19], is the most serious limitation of SPME for routine monitoring of PAHs. 

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