Bubble cells, electrophoresis

The Hb solutions generally used are obtained by simple osmotic hemolysis of normal red cells followed by elimination of the ghosts. The molecular heterogeneity of such solutions of adult Hb is revealed by the starch-gel electrophoresis. The Hb line is therefore not quite distinct, which is a minor drawback when the solutions are used for Hp typing. To stabilize the Hb solutions, it is advisable to bubble CO through them before they are ampouled and stored in the frozen state. 

In electrophoresis an electric field is applied to a sample causing charged dispersed droplets, bubbles, or particles, and any attached material or liquid to move towards the oppositely charged electrode. Their electrophoretic velocity is measured at a location in the sample cell where the electric field gradient is known. This has to be done at carefully selected planes within the cell because the cell walls become charged as well, causing electro-osmotic flow of the bulk liquid inside the cell. From hydrodynamics it is found that there are planes in the cell where the net flow of bulk liquid is zero, the stationary levels, at which the true electrophoretic velocity of the particles can be measured. 

Good descriptions of practical experimental techniques in conventional electrophoresis can be found in Refs. [81,253,259]. For the most part, these techniques are applied to suspensions and emulsions, rather than foams. Even for foams, an indirect way to obtain information about the potential at foam lamella interfaces is by bubble electrophoresis. In bubble microelectrophoresis the dispersed bubbles are viewed under a microscope and their electrophoretic velocity is measured taking the horizontal component of motion, since bubbles rapidly float upwards in the electrophoresis cells [260,261]. A variation on this technique is the spinning cylinder method, in which a bubble is held in a cylindrical cell that is spinning about its long axis (see [262] and p.163 in Ref. [44]). Other electrokinetic techniques, such as the measurement of sedimentation potential [263] have also been used. 

Make the acrylamide/urea solution up to 99 ml with H20, add 0.8 ml 10% ammonium persulphate and 50 p TEMED (NNN N -Tetramethylethylene-diamine). Mix briefly by swirling and pour into the electrophoresis cell (Section 3.1.2.) making sure that no bubbles are trapped in the gel mixture. Insert the slot former (12—20 slots) made from a piece of Plasticard (Fig. 3.3.), place the gel raised slightly from the horizontal and put a weight over the top of the gel to ensure a tight fit of the slot former. 

In order to build on this information, experiments for obtaining the f-potential of the pure water-vap)our Interface have been carried out. Such experiments are not easy. First, the water must be extremely pure even trace amounts of impurities, leaching from vessel walls or CO from the atmosphere might adsorb at the interface and drastically affect the outcome. If carried out in cells, electro-osmosis has to be eliminated, or aecounted for. Then, it is difficult to carry out electrophoresis on rising bubbles and, finally, as LG interfaces in their pristine state carmot resist slip, the Helmholtz-Smoluchowskl equation (11.4.3,4) has to be modified. 

After the run, a gel slice containing the RNA region is cut out with a scalpel or razor blade. The gel slice is put into the electrophoresis cell perpendicularly to the long axis, and set into the cell in a manner similar to that described above. The new acrylamide solution (20%) is poured into the cell and allowed to polymerise around and below the 10% strip. Because the 20% gel adheres tenaciously to the Perspex apparatus, it was found necessary to coat with fluorocarbon both the slot former and a region of about 2 cm around the two sides and bottom of the coolant plates that are in direct contact with the gel. Unless the cell is treated in this way, it is very difficult to remove the slot former after polymerisation or to dismantle the apparatus after the run. While the 20% gel polymerises, coolant is circulated to prevent the accumulation of air bubbles between the gel and the plates. Electrophoresis in the second dimension is carried out as in the first, but over a period of 17 hr at the same voltage. 

Recently, the microelectrophoretic technique received two improvements [21]. First, electrodes were designed in such a manner that micrometer-sized bubbles are produced over the entire cross-section of the electrophoresis cell, which allows to select a bubble easily in the stationary plane. Second, a motorized vertical translation stage controlled by a computer is implemented. Thus, when bubbles rise, the electrophoresis cell mounted on the translation stage is made to move downward so that the bubbles can be kept in the field of view of the microscope. As a result, the movement of bubbles with diameters up to 80 p-m can be readily followed and bubble trajectory can be traced for 4-8 sec. 

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