Extraction techniques ultrafiltration

Alternative sample extraction techniques include an approach that combines the deproteinizing efficiency of dichloromethane with the ion-pairing ability of phenylbutazone for isolating tetracyclines from eggs (308). Another approach that was employed for extracting oxytetracycline from milk (285) or swine tissues (309), and tetracycline, oxytetracycline, and chlortetracycline from milk (284), was based on ultrafiltration. With ultrafiltration, however, not all low molecular-mass proteins are retained in the cut-off filters while interfering substances pass through the filter. 

Simjouw, J.-E, Minor, E. C., and Mopper, K. (2005). Isolation and characterization of estuarine dissolved organic matter Comparison of ultrafiltration and C18 solid-phase extraction techniques. Mar. Chem. 96, 219-235. 

Both column chromatography and HPLC are used routinely for sample preparation, particularly for protein samples after particulate contamination has been removed by filtration or centrifugation. In addition, the use of ultrafiltration or solid-phase extraction techniques prior to chromatography often will result in a simplified, more concentrated sample. 

A variety of spectroscopic techniques have been applied to DOC isolated from seawater by cross-flow ultrafiltration or adsorption onto XAD resins. The two techniques isolate very different organic fractions from seawater. Hydrophobic fractions (such as marine humic material) are isolated on XAD resins [48], whereas the organic matter extracted by ultrafiltration is retained primarily on the basis of its molecular size and shape [49], resulting in isolates rich in nitrogen and carbohydrates (polysaccharides). Nuclear magnetic resonance (NMR) spectroscopy has proven successful in distinguishing between the specific structures of XAD-bound humics and the carbohydrates concentrated into colloidal size fractions. 

This section discusses the ultrafiltration, microwave-assisted, and ultrasound-assisted extraction techniques. 

The recovery of proteins from cultivation medium is usually performed by precipitation, adsorption, flocculation, extraction and ultrafiltration [62-64]. The adsorptive bubble separation techniques were considered in a book by Lemlich [65]. Foam flotation was described by Wilson and Clark [66]. However, in these books, no systematic investigations on the influence of equipment and operating parameters on protein enrichment and separation factors were published. 

The major sample preparation techniques that are amenable to automation are solid-phase extraction, LC, dialysis, microwave sample preparation, flow injection analysis, and segmented flow analysis. Other sample preparation techniques, such as liquid-liquid extraction or ultrafiltration, may be possible to automate but may not be cost effective. This shortlist of amenable techniques may constrain an analysis, but there is a large body of experience in the literature to help a novice to use these procedures. 

Some new green extraction techniques, aimed at sparing energy and reducing costs, such as solid state and submerse fermentation, enzymatic, microwave- or ultrasound-assisted extraction, ultrafiltration, flash distillation and controlled pressure drop processing [22, 23] have been studied to improve solvent 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. 

Clearly, one option to reduce the add-on is to use high-efficiency size formulations. However, there is a limit to what can be achieved by this approach. Even if the add-on is reduced to only 5%, the pollution load is still substantial. The two main options to facilitate disposal are (a) recovery of size polymers and (b) biological effluent treatment. Recovery of size polymers, particularly from water-soluble synthetic sizes, is based on extraction washing using the minimum quantity of water. Recovery rates in the region of 50% have been quoted for polyfvinyl alcohol) and carboxymethylcellulose size formulations. It is necessary to apply one of three concentration techniques precipitation, condensation or ultrafiltration [205]. 

The same advantages are exhibited by LC in comparison with techniques such as fractional crystallisation, liquid extraction, ultrafiltration and adsorption. It has already been pointed out (Section 19.6) that LC now plays a major part in bioseparations, where the technique needs to be integrated into the process train as part of a systems approach. 

Several strategies have been described for the preconcentration of sample components present at low concentrations. These techniques include zone sharpening,28-29 on-line packed columns,30 and transient capillary isotachophoresis (cITP).31-32 Other standard laboratory techniques are often used, including solid-phase extraction, protein precipitation, ultrafiltration, etc. Two important points to keep in mind when selecting a concentration protocol are the sample requirements of the method and the potential selectivity on relative concentrations of sample components. The latter point applies to purity and concentration analysis. 

This technique of MEUF has also been successfully employed for the recovery of thuringiensin [258], removal of cresols [262], extraction of chromate anion [257], removal of dissolved organic pollutants [256], removal of -alcohols [263],preconcentration and removal of iron [260], and preconcentration of aniline derivatives [261].Kandori and Schechter [264] have given a detailed account of selecting surfactants for MEUF. The design characteristics of micellar enhanced utrafilters and cross-flow ultrafiltration of micellar surfactant solutions have been described by Markets et al. [265]. 

Various processing techniques, other than fermentation, can be utilized to remove phytic acid and other dietary fiber materials that reduce mineral absorption (109). Processes would include differential extraction and filtration techniques such as ultrafiltration (125, 126, 127). 

Ultrafiltration (278, 279) and immunoaffinity chromatography (282) have also been described for removal of matrix components from milk extracts, while online trace enrichment has been reported for isolation/purification of tetracycline, oxytetracycline, demeclocycline, and chlortetracycline residues from animal tissues and egg constituents (305). The latter technique involves trapping of the analytes onto a metal chelate affinity preconcentration column (Anagel-TSK Chelate-5PW), rinsing of coextracted materials to waste, and finally flushing of the concentrated analytes onto the analytical column. 

Techniques can be classified into two main categories those that detect total metal concentrations and those that detect some operationally defined fraction of the total. Methods which detect total concentrations such as inductively coupled plasma spectrometry, neutron activation analysis, atomic absorption spectrometry and atomic emission spectrometry have no inherent speciation capabilities and must be combined with some other separation technique(s) to allow different species to be detected (approach A in Fig. 8.2). Such separation methods normally fractionate a sample on the basis of size, e.g. filtration/ultrafiltration, gel filtration, or a combination of size and charge, e.g. dialysis, ion exchange and solvent extraction (De Vitre et al., 1987 Badey, 1989b Berggren, 1989 1990 Buffle et al., 1992). In all instances the complexes studied must be relatively inert so that their concentrations are not appreciably modified during the fractionation procedure. 

Prior to metabolomic analysis, sample treatment is typically needed, as CSF contains approximately 0.3 mg/mL protein (114) that may hinder metabolite analysis. Consequently, CSF sample treatment is essentially directed to protein removal by means of organic solvent addition (84,88) or by ultrafiltration (85,89,90). The final metabolic extract composition will depend in a great extent on the sample treatment (115), and it will be selected mostly regarding the metabolomic approach and the analytical technique that will be afterward applied. 

One of the drawbacks of ion exchange chromatography is the need for a secondary technique to remove inorganic salts from the purified product. Desalting can often be performed by ultrafiltration, solid phase extraction or by gel filtration. The latter mode of separation is described briefly in Section 3.5. 

Primary recovery of the active ingredient from the solid or liquid phase to remove large quantities of unwanted waste materials, which may themselves be processed further. Suitable techniques include solvent extraction, precipitation by chemical or physical changes to the product-containing solution, and ultrafiltration or microfiltration to separate products above a particular size. Work done on combined biomass separation-primary product recovery processes such as expanded-bed adsorption are now being commercialized in the pharmaceutical industry. 

Enormous advances and growth in the use of ordered media (that is, surfactant normal and reversed micelles, surfactant vesicles, and cyclodextrins) have occurred in the past decade, particularly in their chromatographic applications. New techniques developed in this field include micellar liquid chromatography, micellar-enhanced ultrafiltration, micellar electrokinetic capillary chromatography, and extraction of bioproducts with reversed micelles techniques previously developed include cyclodextrins as stationary and mobile-phase components in chromatography. The symposium upon which this book was based was the first major symposium devoted to this topic and was organized to present the current state of the art in this rapidly expanding field. 

The comparative use of MEKC, CZE, and capillary isotachophoresis (CITP) for the determination of drugs in body fluids was reported by Caslavska et al. (1993). Salicylate, paracetamol, and antiepilectics in serum and urine were analyzed with the three techniques. In case of high drug concentrations, body fluids could be injected directly, or with simple dilution (for urine) or ultrafiltration (for serum). Extraction and concentration were necessary for... 

The majority of reports have used electrospray ionization mass spectroscopy (ESI-MS) as an analytical detection method because of its sensitivity and the soft namre of its ionization procedure, which generally only leads to the detection of the molecular ions of the positive library members. Many separation techniques have been coupled to ESI-MS, including affinity chromatography (49), size exclusion chromatography (50, 51), gel filtration (52), affinity capillary electrophoresis (53-58), capillary isoelectric focusing (59), immunoaffinity ultrafiltration (60), and immunoaffinity extraction (61). ESI-MS has also been used alone (62) to screen a small carbohydrate library. Other examples reported alternative analytical techniques such as MALDI MS, either alone (63, 64) or in conjunction with size exclusion methods (65), or HPLC coupled with immunoaffinity deletion (66). 

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