Capillary migration

Rule, G. S., Montagna, R. A., and Durst, R. A. (1997) Characteristics of DNA-tagged liposomes allowing their use in capillary-migration, sandwich-hybridization assays. Anal Biochem. 244, 260-269... 

Here colloidal gold for conjugation is used as available detection system. The signal reagent is solubilized and binds to the antigen or antibody in the sample and moves through the membrane by capillary migration. The tests can be run individually or... 

In Fig. 32.2 the capillary on the top contains an ionic liquid whose ions are under the influence of an electric field created by the high voltage power supply. This field is created between the capillary and the plate surface at the bottom. The positively charged ions at the capillary migrate to the liquid/air interface and deform the fluid surface into a conical shape [5]. At the capillary and plate surfaces, the ions complete reduction and oxidation reactions and, therefore, resemble an electrolytic ceU. The nature of these reactions is described in detail in [6]. 

Horizontal systems have been used mainly for heterogeneous bioassay where the separation of the free and bound labeled molecules is accomplished by capillary migrations through the carrier element. 

Thermo-capillary migration (temperature gradients) may dominate the gravitational body force for very small droplets, less than 1 pm. 

This simple procedure requires a micropipette with which a small volume (a few microliters or less) is directly dropped on the support either once or repetitively to obtain thicker membranes. The drop-coated surface is then dried at ambient conditions or cured at elevated temperatures. Important for the quality and uniformity of the cast layer is the surface roughness and its wettability with the membrane solution which can be estimated via hydrophilicity-lipophilicity considerations or contact angle measurements. Chromatographic and capillary migration effects can be the reason for inhomogenities as well. 

In order to eliminate flaws inherent to thermal debinding and to shorten the duration of this stage, other techniques for the extraction of organic shaping additives have been developed. These techniques are based on an under- or overpressure of the treatment atmosphere, on microwave heating, capillary migration of molten binder, sublimation of a binder in aqueous phase, or solubilization by catalytic reaction or solvents. 

The column is swept continuously by a carrier gas such as helium, hydrogen, nitrogen or argon. The sample is injected into the head of the column where it is vaporized and picked up by the carrier gas. In packed columns, the injected volume is on the order of a microliter, whereas in a capillary column a flow divider (split) is installed at the head of the column and only a tiny fraction of the volume injected, about one per cent, is carried into the column. The different components migrate through the length of the column by a continuous succession of equilibria between the stationary and mobile phases. The components are held up by their attraction for the stationary phase and their vaporization temperatures. 

In capillary electrophoresis the conducting buffer is retained within a capillary tube whose inner diameter is typically 25-75 pm. Samples are injected into one end of the capillary tube. As the sample migrates through the capillary, its components separate and elute from the column at different times. The resulting electrophero-gram looks similar to the chromatograms obtained in GG or HPLG and provides... 

Electroosmotic Mobility When an electric field is applied to a capillary filled with an aqueous buffer, we expect the buffer s ions to migrate in response to their electrophoretic mobility. Because the solvent, H2O, is neutral, we might reasonably expect it to remain stationary. What is observed under normal conditions, however, is that the buffer solution moves toward the cathode. This phenomenon is called the electroosmotic flow. 

Examining equation 12.41 shows that we can decrease a solute s migration time (and thus the total analysis time) by applying a higher voltage or by using a shorter capillary tube. Increasing the electroosmotic flow also shortens the analysis time, but, as we will see shortly, at the expense of resolution. 

Capillary Zone Electrophoresis The simplest form of capillary electrophoresis is capillary zone electrophoresis (CZE). In CZE the capillary tube is filled with a buffer solution and, after loading the sample, the ends of the capillary tube are placed in reservoirs containing additional buffer solution. Under normal conditions, the end of the capillary containing the sample is the anode, and solutes migrate toward... 

The direction of electroosmotic flow and, therefore, the order of elution in CZE can be reversed. This is accomplished by adding an alkylammonium salt to the buffer solution. As shown in Figure 12.45, the positively charged end of the alkylammonium ion binds to the negatively charged silanate ions on the capillary s walls. The alkylammonium ion s tail is hydrophobic and associates with the tail of another alkylammonium ion. The result is a layer of positive charges to which anions in the buffer solution are attracted. The migration of these solvated anions toward... 

Capillary zone electrophoresis also can be accomplished without an electroosmotic flow by coating the capillary s walls with a nonionic reagent. In the absence of electroosmotic flow only cations migrate from the anode to the cathode. Anions elute into the source reservoir while neutral species remain stationary. 

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

Two different mixtures of peptides and alkaloids (qv) have been analy2ed by ce/uv/ms using sims to determine whether this technique can detect trace impurities in mixtures (85). The first mixture consisted of two bioactive peptide analogues, which included Lys-bradykinin (kahidin) and Met-Lys-bradykinin. The presence of 0.1% Lys-bradykinin was detected by sim ce/ms but not by ce/uv at 0.1% level as it migrated from the capillary column prior to the main component, Met-Lys-bradykinin. The second mixture consisted of two antibacterial alkaloids, berberine and palmitine. The presence of 0.15% palmitine was detected by ce/uv and sim ce/ms at 0.15% level as it migrated from the capillary column, following the main component berberine. This technique can provide a complementary technique for trace components in such sample mixtures. 

Most of the surfaces that require repellent treatments are not smooth but contain capillaries into which a Hquid can migrate, even though the advancing contact angle of the Hquid on the surface is >0°. The law for the movement of Hquids into an idealized capillary is given by the equation ... 

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