Electrophoresis media

The structure of these gel-like systems of micelles is very different from that of conventional electrophoresis media made from chemically and physically cross-linked polymers of polyacrylamide and agarose [75], The absence of chemical or physical cross-links in the Pluronic gel-like phases may allow a larger degree of freedom for macromolecular transport around the obstacles that make up the medium than occurs in conventional electrophoresis media. 

Harrington, MG Lee, KH Bailey, JE Hood, LE, Sponge-Like Electrophoresis Media Mechanically Strong Materials Compatible with Organic Solvents, Polymer Solutions and Two-Dimensional Electrophoresis, Electrophoresis 15, 187, 1994. 

Capillary electrophoresis (CE) MS is another technique used to separate and measure the m/z ratios of a mixture of peptides and proteins. In this method, the peptide mixture is separated by different migration rates through the electrophoresis media and the effluent is again directly sprayed into the mass spectrometer using a micro ESI device. This method is capable of femtomole or lower detection limits and is further discussed in a review. In 1996, a group at the University of Washington described a solid phase extraction (SPE) capillary electrophoresis MS-MS approach for the analysis of peptides and showed limits of detection at the 100 s of attomole level. " ... 

When fresh rat vesicular secretion (or acetone-desiccated proteins therefrom) is subject to SDS-polyacrylamide gel electrophoresis at neutral or mildly alkaline pH, the relative migration and staining intensity of bands of proteins or their subunits are conspicuously dependent on the presence of concentrated urea and(or) thiols in the preparative and electrophoresis media. Thiols apparently promote ex-... 

The other reactions at the electrodes produce acid (anode) and base (cathode) so that there is a possibiUty of a pH gradient throughout the electrophoresis medium unless the system is well buffered (see Hydrogen-ion activity). Buffering must take the current load into account because the electrolysis reactions proceed at the rate of the current. Electrophoresis systems sometimes mix and recirculate the buffers from the individual electrode reservoirs to equalize the pH. 

The electrophoretic mobfiity is directly proportional to the net charge and inversely proportional to the size of the molecule and the viscosity of the electrophoresis medium. In practice the equation p,= cmV(V)(s) is used to calculate the electrophoretic mobility. Thus if albumin travels 3 cm (/) on a 10-cm (d) long agarose gel and does so in 75 minutes (or 75 X 60s) at a voltage of 250 V, then... 

By incorporating methylmercuric hydroxide into agarose gel, a gel electrophoresis medium effectively containing a denaturing agent has been prepared and applied to the study of RNA s from avian myeloblastosis virus. ... 

FIGURE 2. Temperature dependence of electrokinetic zeta potential and ACMA binding in broken chloro-plasts and the effect of energization. The free-flow electrophoresis medium contained 345 mM sorbitol, 2 mM Tricine buffer, pH 8.0, 20 yM methylviologen and 10 yg Chl/ml. ACMA binding was determined by fluorescence measurements in the same medium with 40 yg Chi/ ml and 5 yM ACMA. 

Electrophoresis is used primarily to analyze mix tures of peptides and proteins rather than individual ammo acids but analogous principles apply Because they incorporate different numbers of ammo acids and because their side chains are different two pep tides will have slightly different acid-base properties and slightly different net charges at a particular pH Thus their mobilities m an electric field will be differ ent and electrophoresis can be used to separate them The medium used to separate peptides and proteins is typically a polyacrylamide gel leading to the term gel electrophoresis for this technique... 

Electrophoresis and electro osmosis can be used to enhance conventional cake filtration. Electrodes of suitable polarity are placed on either side of the filter medium so that the incoming particles move toward the upstream electrode, away from the medium. As most particles carry negative charge, the electrode upstream of the medium is usuaHy positive. The electric field can cause the suspended particles to form a more open cake or, in the extreme, to prevent cake formation altogether by keeping aH particles away from the medium. 

Electrical Enhancement of Dewatering. Electrophoresis (qv) can be used to prevent a filter cake from forming on a filter medium while allowing water to pass through the medium from the slurry. Electrophoresis is used to move the particles upstream, opposite to the Hquid movement, in order to prevent blinding of the medium. 

Generation of Heat in Electric Fields. One of the practical problems encountered in electrophoresis is the generation of heat from resistive dissipation of energy in the electrophoretic medium. The generation of heat (foule heating) is given by... 

Electrolysis Reactions. The electrodes in electrophoresis equipment are typically constmcted from platinum wire, and sodium chloride generally carries the bulk of the current in any electrophoretic medium. This results in the reactions... 

Paper Electrophoresis. Paper (qv) as an electrophoretic matrix was employed in some of the first electrophoretic techniques developed to separate compounds. Paper is easier than a gel matrix because the paper matrix requires no preparation. Besides being easy to obtain, paper is a good medium because it does not contain many of the charges that interfere with the separation of different compounds. Two types of paper employed in this type of electrophoresis are Whatman 3 MM (0.3 mm) and Whatman No. 1 (0.17 mm). 

Capillary Electrophoresis. Capillaries were first appHed as a support medium for electrophoresis in the early 1980s (44,45). The glass capillaries used are typically 20 to 200 p.m in diameter (46), may be filled with buffer or gel, and are frequendy coated on the inside. Capillaries are used because of the high surface-to-volume ratio which allows high voltages without heating effects. The only limitations associated with capillaries are limits of detection and clearance of sample components. 

Process Concept The application of a direct elecdric field of appropriate polarity when filtering should cause a net charged-particle migration relative to the filter medium (electrophoresis). The same direct electric field can also be used to cause a net fluid flow relative to the pores in a fixed filter cake or filter medium (electroosmosis). The exploitation of one or both of these phenomena form the basis of conventional electrofiltration. 

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