Solid-phase extraction tools

Online Solid Phase Extraction as Tool for High-Throughput... 

Liquid-solid extraction methods coupled to LC-DAD are gaining interest for the screening of pesticides in waters. Automated precolumn technology involving disposable solid-phase extraction precolumns has proved to be a useful tool. A C18 precolumn was used online by LC-DAD. In these conditions, 11 OPPs were analyzed in groundwater (49). 

The combination of solid-phase extraction (SPE) with HPLC analysis or preparative HPLC can be a valuable tool in concentrating and identifying degradation products. SPE can be a useful technique for the isolation and concentration of analytes from a complex mixture. Selection of the appropriate column depends on the properties of the API and the suspected degradants (70,71). Mixed mode columns having both non-polar and ion... 

It is too often assumed that because precolumn sample preparation devices, such as solid-phase extraction cartridges, are simple tools, they require relatively little skill or attention to detail for successful use. Cartridges do, however, require attention to detail for successful operation in sample enrichment procedures. Two of the most important parameters to control and understand are flow-rate effects and recovery (or loadability) effects. 

Within the pharmaceutical industry there has always been a need for sample purity. Any compound that is a potential drug candidate can only be fully characterised and tested once it is available in a pure form. There are many purification tools available for sample clean-up, e.g. flash chromatography, solid phase extraction, etc. 1-31. However, for the more complex purification problems where the desired compound and its associated contaminants have very similar polarities, structures, etc., preparative chromatography is the method of choice due to its superior separative capabilities. Preparative chromatography can also be scaled up from lens of milligrams to tens or even hundreds of grams of compound. The other main factor in favour of this technique is its ability to be tailored for most classes of compound. 

In summary, non-covalently imprinted polymers offer a universal tool for sensor technology, besides the main applications in HPLC and solid phase extraction. The examples discussed above are but a few of the potential applications of smart chemosensory devices coated with non-covalent MIPs. The strategy of non-covalent imprinting is highly appropriate for sensory applications. Antibody-like... 

Paleologos, E.K. and Kontominas, M.G. (2004) On-line solid-phase extraction with surfactant accelerated on-column derivatization and micellar liquid chromatographic separation as a tool for the determination of biogenic amines in various food substrates, Anal. Chem., 76, 1289-1294. 

Hennion, M.-C. Cau-Dit-Coumes, C. Pichon, V. Trace Analysis of Polar Organic Pollutants in Aqueous Samples Tools for the Rapid Prediction and Optimisation of the Solid-Phase Extraction Parameters, J. Chromatogr. A 823(1-2), 147-161 (1998). 

An understanding of the mechanisms of solid-phase extraction (SPE) are crucial for effective methods development. The four mechanisms outlined in Chapter 2 are sufficient for the majority of SPE and are an effective set of tools for methods development. The molecule s structure and the sample matrix are the main features used to choose a mechanism of isolation and separation. This chapter will discuss a six-step approach to methods development, how to execute the SPE recovery experiment, troubleshooting and optimizing conditions for the SPE recovery experiment, and how to critically evaluate previously published methods. 

The second type of automation is the workstation. They are instruments that can perform multiple functions using software tools and dedicated hardware to perform a set of predefined operations, which are related to or part of the process of solid-phase extraction. They differ from laboratory robots that are capable of many laboratory functions. There are seven instruments that will be discussed in this section (Table 10.2-10.8), which are dedicated to solid-phase extraction. They range in price from approximately 20,000 to 50,000 (1996 dollars) for workstations and from 50,000 and up for laboratory robots. 

Nilsson, U.J. (2000) Solid-phase extraction for combinatorial libraries. J. Chromatogr. A 885 305-319. Takahashi, T. (2001) New tools for isolation and analysis in combinatorial chemistiy. Chromatography 22 45 -48. Schultz, L., Garr, C.D., Cameron, L.M. and Bukowski, J. (1998) High throughput purification of combinatorial libraries. Bioorg. Med. Chem. Lett. 8 2409-2414. 

For biomarker identification, it is also possible to separate out substances of interest from a complex biofluid sample using techniques such as solid phase extraction or HPLC. For metabolite identification, directly coupled chromatography-NMR spectroscopy methods can be used. The most powerful of these hyphenated approaches is HPLC-NMR-MS [24] in which the eluting HPLC peak is split with parallel analysis by directly coupled NMR and MS techniques. This can be operated in on-flow, stopped-flow, and loop-storage modes and thus can provide the full array of NMR and MS-based molecular identification tools. These include MS-MS for identification of fragment ions and FT-MS or TOF-MS for accurate mass measurement and hence derivation of molecular empirical formulae. 

Solid phase extraction (SPE) was developed during the last 10 years as an effective analytical tool for the isolation and purification of a wide range of compounds. For many applications in pharmacy and biomedicine, it is playing an increasingly important part in sample preparation both for trace concentrations and for the isolation of substances on a preparative scale [20]. 

Four general classes of NMR experiments are routinely used to analyze metabolites (1) ID NMR experiments (2) 2D NMR experiments (3) Solvent suppression methods and (4) Hyphenated NMR experiments. The ID and 2D NMR experiments are commonly used for metabolite structure determination. The various solvent suppression techniques (Gaggelli and Valensin, 1993 Hwang and Shaka, 1995 Smallcombe and Patt, 1995) are crucial for dilute metabolite samples where the solvent peak is the most intense peak in the NMR spectrum. These solvent suppression techniques can be incorporated as needed in both ID and 2D NMR experiments. Since their introduction in the 1990s, hyphenated NMR methods have become common tools in the identification of metabolites. These methods include LC-NMR (Albert, 1995 Spraul et al., 1993, 1994), LC-NMR-MS (Mass Spectrometry) (Shockcor et al., 1996) and LC/SPE (solid phase extraction)/NMR (Alexander et al., 2006 Bieri et al., 2006 Xu et al., 2005 Wilson et al., 2006). 

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