Sample preparation membrane extraction

Until this point, the sample preparation techniques under discussion have relied upon differences in polarity to separate the analyte and the sample matrix in contrast, ultraflltration and on-line dialysis rely upon differences in molecular size between the analyte and matrix components to effect a separation. In ultrafiltration, a centrifugal force is applied across a membrane filter which has a molecular weight cut-off intended to isolate the analyte from larger matrix components. Furusawa incorporated an ultrafiltration step into his separation of sulfadimethoxine from chicken tissue extracts. Some cleanup of the sample extract may be necessary prior to ultrafiltration, or the ultrafiltration membranes can become clogged and ineffective. Also, one must ensure that the choice of membrane filter for ultrafiltration is appropriate in terms of both the molecular weight cut-off and compatibility with the extraction solvent used. 

In one study by Hood et al., 282 of 1153 identified proteins were identified by at least 2 unique tryptic peptides from FFPE prostate cancer (PCa) tissue.9 According to the gene ontology classification of the proteins identified, -65% of proteins were predicted to be intracellular proteins, while -50% of the total human proteome is predicted to be located in the intracellular compartment. Additionally, 20% of the proteins identified in the PCa tissue were classified as membrane proteins, which is significantly less than the predicted 40% for the human proteome. This relative disparity is not unexpected, considering the Liquid Tissue sample preparation kit lacks specific protocols for membrane protein extraction. The Liquid Tissue method has also been used for proteomics studies of a variety of FFPE tissue samples, including pancreatic tumors,28 squamous cell carcinoma,4 and oral human papillomavirus lesions.27... 

In 2003, Smith reviewed newer sample preparation techniques, including pressurized liquid extraction, solid phase microextractions, membrane extraction, and headspace analysis. Most of these techniques aim to reduce the amount of sample and solvent required for efficient extraction. 

Rule G, Henion J. 1999. High-throughput sample preparation and analysis using 96-weU membrane solid-phase extraction and liquid chromatography—tandem mass spectrometry for the determination of steroids in human urine. J Am... 

However, the solution obtained after denaturation might include, depending on the application, other components besides the liberated marker ( matrix ). If a small amount of target material is used in the binding assay, the quantity of remaining matrix will be so low that it hardly disturbs the quantitation and the sample can be measured directly by LC-MS without further sample preparation (e.g. membrane filtration or solid phase extraction [78]). 

The nature of the association between membrane and teichoic acid is unknown, and it is possible that these teichoic acids are chemically attached to other components of the cell. Samples obtained by extraction with phenol appear to have appreciably higher molecular weight than has the purified teichoic acid obtained by extraction with trichloroacetic acid, and it is likely that the prolonged, acid treatment used in earlier work may have caused hydrolysis of some of the phosphodiester linkages. It is noteworthy that this comment on earlier studies does not apply to ribitol teichoic acids. Detailed examination of preparations of membrane teichoic acid obtained by less drastic conditions is highly desirable, in order to confirm the supposed size of the naturally occurring polymers, as well as... 

When samples contain high quantities of interfering material (e.g., sugars, colloids), a sample-cleanup procedure is recommended. A sample preparation with solid-phase extraction cartridges (C18) was found to be quite useful and effective (180,193). Prior to HPLC analysis, all samples should be filtered through a 0.45-/zm or smaller membrane filter. 

Janiszewski, J. Schneider, P. Hoffmaster, K. Swyden, M. Wells, D. Fouda, H. 1997. Automated sample preparation using membrane microliter extraction for bioanalytical mass spectrometry. Rapid Cornmun. Mass Spectrom., 11,1033-1037. 

As a corollary to this, more direct sample preparation procedures have been the pursuit of many scientists, who believe that miniaturization of analytical techniques can be a key solution to many of the unwanted drawbacks of LLE and SPE. Currently, several miniaturized extraction systems have been investigated, which are based primarily on utilizing downsized liquid, solid, or membrane extraction phases. 

Jonsson, J.A. and L. Mathiasson. 1999. Liquid membrane extraction in analytical sample preparation I. Principles. Trends Anal. Chem. 18 318-325. 

Sandahl, M., L. Mathiasson, and J.A. Jonsson. 2002. On-line automated sample preparation for liquid chromatography using parallel supported liquid membrane extraction and microporous membrane liquid-liquid extraction. J. Chromatogr. A 975 211-217. 

Jonsson, J.A. (2003) Membrane extraction for sample preparation - a practical guide. Chromatographia, 57, S317. 

Chimuka, L., Cukrowska, E. and (onsson, J.A. (2004) Why liquid membrane extraction is an attractive alternative in sample preparation. Pure and Applied Chemistry, 76, 707. 

There are many techniques available for the preparation of volatile analytes prior to instrumental analysis. In this chapter the major techniques, leading primarily to gas chromatographic analysis, have been explored. It is seen that the classical techniques purge and trap, static headspace extraction, and liquid-liquid extraction still have important roles in chemical analysis of all sample types. New techniques, such as SPME and membrane extraction, offer promise as the needs for automation, field sampling, and solvent reduction increase. For whatever problems may confront the analyst, there is an appropriate technique available the main analytical difficulty may lie in choosing the most appropriate one. 

Jakubowska, N., Polkowska, Z., Namiesnik, J., Przyjazny, A. Analytical applications of membrane extraction for biomedical and environmental liquid sample preparation. Crit. Rev. Anal. Chem. 35, 217-235 (2005)... 

Membrane Techniques The interest in membrane techniques for sample preparation arose in the 1980s. Extraction selectivity makes membrane techniques an alternative to the typical sample enrichment methods of the 1990s. Different membrane systems were designed and introduced into analytical practice some more prominent examples are polymeric membrane extraction (PME), microporous membrane liquid-liquid extraction (MMLLE), and supported liquid membrane extraction (SEME) [106, 107]. Membrane-assisted solvent extraction (MASE) coupled with GC-MS is another example of a system that allows analysis of organic pollutants in environmental samples [108-111] ... 

Membrane extraction with sorbent interface (MESI) is an interesting example of an extraction device, which is the most useful system for interfacing with GC. In this approach, the donor phase is a gas or a liquid sample, and the acceptor phase is a gas. The volatiles are continuously trapped on sorbent and then desorbed into GC [112]. Another solution is a combination of off-line GC-MESI through a cryogenic trap, which allows preparation of environmental samples in the field and performance of GC analysis after transportation to the laboratory [113,114]. MESI allows the extraction of volatile and relatively nonpolar analytes. 

Matz, G., Kibelka, G., Dahl, J., Leimeman, F. Experimental study on solvent-less sample preparation methods - membrane extraction with a sorbent interface, thermal membrane desorption application and purge-and-trap. J. Chromatogr. 830, 365-376 (1999)... 

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