Electrophoresis types

Francis, G.A. and O Beime, D. 2006. Isolation and pulsed-field gel electrophoresis typing of Listeria monocytogenes from modified atmosphere package fresh-cut vegetables collected in Ireland. Journal of Food Protection 69 2524—2528. 

All these effects may lead to the conclusion that some kind of sample pretreatment is often essential varying from simple dilution to decomposition and separation. For not too complex systems separation can be elegantly accomplished with capillary electrophoresis type pTAS. 

The most familiar type of electrokinetic experiment consists of setting up a potential gradient in a solution containing charged particles and determining their rate of motion. If the particles are small molecular ions, the phenomenon is called ionic conductance, if they are larger units, such as protein molecules, or colloidal particles, it is called electrophoresis. 

FIGURE 27 3 Application of electrophoresis to the separation of aspartic acid alanine and lysine according to their charge type at a pH corresponding to the isoelectric point (pi) of alanine... 

Injecting the Sample The mechanism by which samples are introduced in capillary electrophoresis is quite different from that used in GC or HPLC. Two types of injection are commonly used hydrodynamic injection and electrokinetic injection. In both cases the capillary tube is filled with buffer solution. One end of the capillary tube is placed in the destination reservoir, and the other is placed in the sample vial. 

The following experiments may he used to illustrate the application of chromatography and electrophoresis to a number of different types of samples. Experiments are grouped by the type of technique, and each is briefly annotated. 

The last set of experiments provides examples of the application of capillary electrophoresis. These experiments encompass a variety of different types of samples and include examples of capillary zone electrophoresis and micellar electrokinetic chromatography. 

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

Another difference between other types of electrophoresis and disc electrophoresis is that the molecules in a sample do not start to significantly separate until entering the separating gel. A discontinuous gel system may be used with almost any type of 2one electrophoresis appHcation. 

In addition to polymeric support media, capillaries and flowing buffers have been used as support media for electrophoresis. Although these are not used as frequendy, there are definite advantages for certain types of samples and appHcations. 

The use of agarose as an electrophoretic method is widespread (32—35). An example of its use is in the evaluation and typing of DNA both in forensics (see Forensic chemistry) and to study heritable diseases (36). Agarose electrophoresis is combined with other analytical tools such as Southern blotting, polymerase chain reaction, and fluorescence. The advantages of agarose electrophoresis are that it requires no additives or cross-linkers for polymerization, it is not hazardous, low concentration gels are relatively sturdy, it is inexpensive, and it can be combined with many other analytical methods. 

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). 

Modes of Operation There is a close analogy between sedimentation of particles or macromolecules in a gravitational field and their elec trophoretic movement in an electric field. Both types of separation have proved valuable not only for analysis of colloids but also for preparative work, at least in the laboratoiy. Electrophoresis is applicable also for separating mixtures of simple cations or anions in certain cases in which other separating methods are ineffectual. 

FIG. 22-26 Types of arrangement for zone electrophoresis or electrochromatography. (a) Rihhon unit, with d > w cooling at side faces, (h) Block unit, with w > d cooling at electrodes. 

Chiari, M D Alesio, L Consonni, R Righetti, PG, New Types of Large-Pore Polyacrylamide-Agarose Mixed-Bed Matrices for DNA Electrophoresis Pore Size Estimation from Ferguson Plots of DNA Eragments, Electrophoresis 16, 1337, 1995. 

Chiari, M Micheletti, C Nesi, M Fazio, M Righetti, PG, Towards New Formulations for Polyacrylamide Matrices A-Acryloylaminoethoxyethanol, a Novel Monomer Combining High Hydrophilicity with Extreme Hydrolytic Stability, Electrophoresis 15, 177, 1994. Chiari, M Righetti, PG, New Types of Separation Matrices for Electrophoresis, Electrophoresis 16, 1815, 1995. 

Rothe, GM, Determination of Molecular Mass, Stoke radius. Frictional Coefficient and Isomer-Type of Non-denatured Proteins by Time-Dependent Pore Gradient Gel Electrophoresis, Electrophoresis 9, 307, 1988. 

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