Cathodic mobilizer

Use of zwitterions is an alternative approach that provides more effective mobilization of protein zones across a wide pH gradient.83 For example, cathodic mobilization with a low-pi zwitterion enables efficient mobilization of proteins with pis ranging from 4.65 to 9.60. The proposed mechanism for zwitterion mobilization couples a pH shift at the proximal end of the tube with a displacement effect at the distal end as the zwitterion forms an expanding zone within the gradient at its pi. Effective zwitterion mobilization depends on the selection of the appropriate mobilization reagent. 

Proteins or antibodies (36 pg) were mixed with ampholine pH 3.5—9.5 (final concentration of 5%, Amersham Biosciences, distributed by GE Healthcare, Uppsala, Sweden), p7 markers (Bio-Rad, Hercules, CA), and hydroxypropyl methyl cellulose (final concentration of 0.2% HPMC, Sigma-Aldrich, St. Louis, MO). The final protein concentration was 0.3mg/mL. Figure 17 shows a schematic of the sample preparation. The mixture was mixed thoroughly and was introduced to the capillary (eCAP neutral-coated, 50 micron X 30 cm, Beckman, Fullerton, CA) by hydrodynamic injection. Injections were performed using 20 psi for 99 s. The solution was then separated under an electric field of 25 kV for 10 min. The focused protein was then pushed/pulled out of the capillary through a mobilization process using the cathodic mobilizer (Bio-Rad, Hercules, CA). 

After the proteins are focused in the capillary, the isoforms are mobilized past the detector for UV detection. The mobilization step utilizes either hydrodynamic pressure or chemical means. Chemical mobilization can be performed using either ionic or zwitterionic compounds. The general consensus is that hydrodynamic mobilization results in reduced resolution. Bio-Rad (Hercules, CA) zwitterion cathodic mobilizer with chemical mobilization provides superior resolution (Figure 21). 

FIGURE 12 Application of capillary isoelectric focusing (clEF) for the determination of apparent p/ values of rMAb samples. Capillary Bio-Rad Bio-CAP XL capillary (50 pm x 24 cm) ampholyte 80% clEF Bio-Lyte Ampholyte 3-10 (2% solution with 0.5% TEMED, 0.2% HPMC) anolyte 20 mM phosphoric acid catholyte 40 mM sodium hydroxide focusing l5kV (625V/cm) for 5 min mobilization 20 kV (833V/cm) for 25 min with zwitterions (cathodic mobilizer from Bio-Rad) capillary temperature 25°C. (Reprinted from reference 40, with permission.)... 

If we choose conditions where k < k (or k k ), the ratio of N/N will be > 1 (or 1), and one can therefore state that due to the increase in conductivity, achieved by supplementing the anolyte with a cation, the number of protons entering the tube from the anolyte decreases, which gives rise to a pH increase in the tube. Analogous equations can be derived for the cathodic mobilization, where the introduction of an anion in the catholyte will cause a decrease in pH at the cathodic end of the capillary and, therefore, a mobilization of the pH gradient. Sodium or chloride ions are commonly used [19,20] for anodic or cathodic mobilization, respectively. 

For the on-line system, CIEF is performed conventionally in a 20-cm capillary mounted inside an electrospray probe. After focusing, the outlet reservoir (catholyte) is removed and the capillary tip set to 0.5 pm outside of the probe. A sheath liquid of 50% methanol, 49% water, and 1% acetic acid (pH 2.6) pumped with a syringe pump at 3 pL/min produces a stable electrospray. Cathodic mobilization is produced by changing the anolyte to the sheath liquid. The ampholyte ions were observed up to miz 800 and thus did not interfere with the protein signals. 

Cathodic mobility nearly equal to that of a,/S-di-aminopropionic acid. Edeines A and B not resolved from each other Ref As PC... 

FIGURE 6 Separation of proteins by two-step CiEF using electrophoretic mobilization. The ampholytes generated a gradient from pH 3 to 10 after a focusing time of 300 sec in a neutral-coated capillary. Cathodic mobilization was initiated by replacing the catholyte (40-mM NaOH) with an alkaline zwitterion solution, pi, Isoelectric point. 

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. 

Because micelles are negatively charged, they migrate toward the cathode with a velocity less than the electroosmotic flow velocity. Neutral species partition themselves between the micelles and the buffer solution in much the same manner as they do in HPLC. Because there is a partitioning between two phases, the term chromatography is used. Note that in MEKC both phases are mobile. ... 

These facts would suggest that die electrolysis of molten alkali metal salts could lead to the inuoduction of mobile elecU ons which can diffuse rapidly through a melt, and any chemical reduction process resulting from a high chemical potential of the alkali metal could occur in the body of the melt, rather than being conhned to the cathode volume. This probably explains the failure of attempts to produce tire refractoty elements, such as titanium, by elecU olysis of a molten sodium chloride-titanium chloride melt, in which a metal dust is formed in the bulk of the elecU olyte. 

When lithium ions become sufficiently mobile due to heating, they migrate from the anode to the cathode with the reactions shown in Fig. 5.24 and produce open circuit voltages of about 2.5 V under ideal conditions. In... 

In practice the cathodic protection current will be carried in the corrosive environment by more mobile ions, e.g. OH, Na, etc. 

Studies of double carrier injection and transport in insulators and semiconductors (the so called bipolar current problem) date all the way back to the 1950s. A solution that relates to the operation of OLEDs was provided recently by Scott et al. [142], who extended the work of Parmenter and Ruppel [143] to include Lange-vin recombination. In order to obtain an analytic solution, diffusion was ignored and the electron and hole mobilities were taken to be electric field-independent. The current-voltage relation was derived and expressed in terms of two independent boundary conditions, the relative electron contributions to the current at the anode, jJfVj, and at the cathode, JKplJ. 

Figure 13-12. The rccombiniition profiles for an Ol.lil) with an oliinic anode and an injeelion-liinilcd cathode for various ratios of the dcclron/holc mobilities. Reproduced with permission from I45. ...

Another issue that can be clarified with the aid of numerical simulations is that of the recombination profile. Mailiaras and Scott [145] have found that recombination takes place closer to the contact that injects the less mobile carrier, regardless of the injection characteristics. In Figure 13-12, the calculated recombination profiles arc shown for an OLED with an ohmic anode and an injection-limited cathode. When the two carriers have equal mobilities, despite the fact that the hole density is substantially larger than the electron density, electrons make it all the way to the anode and the recombination profile is uniform throughout the sample. 

Figures 12-12 and 12-13 document that trap-free SCL-conduction can, in fact, also be observed in the case of electron transport. Data in Figure 12-12 were obtained for a single layer of polystyrene with a CF -substituted vinylquateiphenyl chain copolymer, sandwiched between an ITO anode and a calcium cathode and given that oxidation and reduction potentials of the material majority curriers can only be electrons. Data analysis in terms of Eq. (12.5) yields an electron mobility of 8xl0 ycm2 V 1 s . The rather low value is due to the dilution of the charge carrying moiety. The obvious reason why in this case no trap-limited SCL conduction is observed is that the ClVquatciphenyl. substituent is not susceptible to chemical oxidation.

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