Cellulose filters

Many continuous extractions involving solid samples are carried out with a Soxhiet extractor (Figure 7.18). The extracting solvent is placed in the lower reservoir and heated to its boiling point. Solvent in the vapor phase moves upward through the tube on the left side of the apparatus to the condenser where it condenses back to the liquid state. The solvent then passes through the sample, which is held in a porous cellulose filter thimble, collecting in the upper reservoir. When the volume of solvent in the upper reservoir reaches the upper bend of the return tube, the solvent and any extracted components are siphoned back to the lower reservoir. Over time, the concentration of the extracted component in the lower reservoir increases. 

The one-pass system consists of a feed tank, filter, pump, and membrane system (Fig. 6). The feed tank contains whiskey at approximately 100° proof. It is filtered through a cellulose filter and then pumped into the membrane system where the separation takes place. Dupont B-10 A ram id hoUow fiber membranes are used in series or parallel and are able to withstand the high pressures, 689—1034 kPa (6.8—10 atm), necessary to achieve separation. 

The liquid was applied and dried on cellulose filter (diameter 25 mm). In the present work as an analytical signal we took the relative intensity of analytical lines. This approach reduces non-homogeneity and inequality of a probe. Influence of filter type and sample mass on features of the procedure was studied. The dependence of analytical lines intensity from probe mass was linear for most of above listed elements except Ca presented in most types of filter paper. The relative intensities (reduced to one of the analysis element) was constant or dependent from mass was weak in determined limits. This fact allows to exclude mass control in sample pretreatment. For Ca this dependence was non-linear, therefore, it is necessary to correct analytical signal. Analysis of thin layer is characterized by minimal influence of elements hence, the relative intensity explicitly determines the relative concentration. As reference sample we used solid synthetic samples with unlimited lifetime. 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Zellen-bildung, /. cell formation, -faser, /. cell fiber. -faserstofF, m. cellulose, -filter, . revolving filter, -fliissigkeit, /. cell fluid, cell sap. 

Air Sample collection on cellulose filter, dry ashed, solvent extracted Biphasic liquid scintillation 1 pCi 95% Bomben et al. 1994... 

Air Cellulose filter dry ashed, dissolved in HNO3/HF, H202/HCI04, purified with anion exchange, TRU-spec columns followed by electrodeposition. a -Spectroscopy 0.023 pCi/sample 102% Goldstein et al. 1997... 

Occupational air (NIOSH Method 7300) Sample collection on cellulose filter ICAP 1 pg/sample NIOSH 1989b... 

The SPOT-synthesis method also employs Fmoc chemistry but uses hydroxyl groups present on cellulose filter paper to derivatize and thereby immobilize (3-alanine groups onto the paper. After deprotection, the 13-alanine groups can be used as platforms for the synthesis of peptide arrays (Fig. 7.5) (Frank, 1992 Gausepohl et al., 1992). This method has been widely used for mapping antigen-antibody interactions as well as protein-DNA, protein-metal and other protein-protein interactions (Reineke et al., 2001). 

Figure 7.5. Peptide array construction by SPOT-synthesis. fl-alanine groups (b-A) interact with the cellulose filter that serves as a planar support. Peptide synthesis then proceeds using Fmoc chemistries using the fl-alanine group as a starting point. The peptide is attached to the filter via its carboxy-terminus. In this case, lysine is added at the second position and various amino acids are present at the amino terminus of the peptide.

Collected on cellulose filter bCollected on glass fiber filter... 

DehnuUe, B., De Saeger, S., Adams, A., De Kimpe, N., and Van Peteghem, C., Development of a hquid chromatography/tandem mass spectrometry method for the simultaneous determination of 16 myco-toxins on cellulose filters and in fungal cultures, Rapid Communications in Mass Spectrometry 20(5), 771-776, 2006. 

Filters collect liquid and solid particles by mechanisms including diffusion, impaction, interception, electrostatic attraction, and sedimentation onto the filter while allowing the gas to pass through. The types commonly used in atmospheric particulate collection are membranes, fibrous mats, or porous sheets. Different filter materials are used depending on the particular type of measurement being carried out, including Teflon, quartz fiber, nylon, silver, cellulose filters, glass fibers, and polycarbonate. The characteristics of each are summarized by Chow (1995). 

Pass solution through an approximately 100-mesh (150-micron aperture, or similar) screen and collect in clean, dry sealable vessel. The solution is too viscous to flow through a membrane or any cellulosic filter. 

Surface Interactions. Loss of strong acid content of atmospheric aerosols was observed and attributed to reaction with basic sites in the glass or cellulose filter matrices commonly used for high-volume sampling of atmospheric aerosols (46, 50). These filter materials, and glass fiber filters of... 

Cellulose filters give unacceptably diffuse colony patterns after lysis and should not be used. Nylon filters should be acceptable, although we have not examined their suitability. 

Ap tamers can be selected in various ways. The most frequently used approaches are affinity chromatography [21] and modified cellulose filtration [4,22]. The choice of method depends on the properties of the target (for example, its capability to be immobilized on a matrix or to be bound to modified cellulose filters) and the aim of selection. If the desired aptamers should, for example, bind molecules on the surface of intact cells, the selection scheme should employ these cells adhering to the surfaces of tissue culture flasks [23]. 

The modified cellulose filter binding separation method is based on the ability of proteins to bind to nitrocellulose and cellulose acetate [27]. This technique is suitable for protein targets or targets that are linked to a protein, for example, biotin-labeled molecules that can form a stable complex with streptavidin, which itself is retained on modified cellulose [28]. 

Similar to the chromatographic selection step, the enrichment of undesired RNA molecules, which may bind to the filter, strep tavidin, or other components of the reaction setup, must be prevented by preselection. For preselection, the RNA pool is passed through a cellulose filter. Unbound RNA is washed from the filter in a small volume of selection buffer. 

The modified cellulose filter binding assay is based on the tight binding of proteins to this kind of filter material. When a protein-nucleic acid mixture is filtered, proteins are retained on the filter while nucleic acids are washed through. However, nucleic acids are also retained on the filter if they are bound to proteins. Thus, free and protein-bound nucleic acids can be separated [43]. 

Despite a preselection procedure, aptamers may be selected that bind to the bare selection matrix, the cellulose filter, or any other component of the selection setup, because the possible binding sites are presented in a large number (compared to... 

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