Charged capillaries

The mechanism by which analytes are transported in a non-discriminate manner (i.e. via bulk flow) in an electrophoresis capillary is termed electroosmosis. Eigure 9.1 depicts the inside of a fused silica capillary and illustrates the source that supports electroosmotic flow. Adjacent to the negatively charged capillary wall are specifically adsorbed counterions, which make up the fairly immobile Stern layer. The excess ions just outside the Stern layer form the diffuse layer, which is mobile under the influence of an electric field. The substantial frictional forces between molecules in solution allow for the movement of the diffuse layer to pull the bulk... 

Negatively charged capillaries had higher EOF than neutral capillaries. 

Several additional instrumental techniques have also been developed for bacterial characterization. Capillary electrophoresis of bacteria, which requires little sample preparation,42 is possible because most bacteria act as colloidal particles in suspension and can be separated by their electrical charge. Capillary electrophoresis provides information that may be useful for identification. Flow cytometry also can be used to identify and separate individual cells in a mixture.11,42 Infrared spectroscopy has been used to characterize bacteria caught on transparent filters.113 Fourier-transform infrared (FTIR) spectroscopy, with linear discriminant analysis and artificial neural networks, has been adapted for identifying foodbome bacteria25,113 and pathogenic bacteria in the blood.5... 

Interactions between the solutes and the capillary wall also have a negative effect on the efficiency in capillary zone electrophoresis. Both hydrophobic interactions and electrostatic interactions of cations with the negatively charged capillary wall can be the cause of solute adsorption. Significant adsorption has been found for high-molecular-weight species, e.g., peptides and proteins. Because of the increased surface-area-to-volume ratio of narrow-bore capillaries, this effect is even more pronounced. 

This is particularly important for large polymeric molecules. Anions are repelled from the negatively charged capillary wall, simplifying methods development since buffer additives or coated capillaries are not required to minimize wall effects [4],... 

Electrospray ionization (ESI) A liquid (volatile solvent) containing the biomolecule is pushed through a very small, charged capillary, creating a fine spray of charged droplets, which, on evaporation, leads to ionization. 

Diffuslophoresis is the counterpart of electrophoresis in that In the former case a concentration gradient is applied, it leads to polarization and motion in the latter case an electric field Is applied, which leads to concentration polarization and motion. When the particles are immobile, as in a porous plug, or when the concentration gradient is applied over a charged capillary the liquid starts to move. This leads to plug or capillary osmosis, the counterpart of electro-osmosis in plugs or capillaries. 

Large-Molecule Analysis of CE-MS by a Positively Charged Capillary... 

J.C. Fair and J.F. Osterle, Reverse electrodialysis in charged capillary membranes. /. Chem. Phys., 54 (8) (1971) 3307. 

A Tran, H Parker, V Levi, M Kunitani. Analysis of recombinant human platelet-derived growth factor by reversed-charge capillary zone electrophoresis. Anal Chem 70 3809-3817, 1998. 

This technique consists in analyzing the masses of positively charged gaseous particles extracted from a solution within a charged capillary (anode) by applying an electrostatic field. The cation-enriched solution at the tip of the capillary is ejected as microscopic drops in direction of a cathodic plate at the entrance of the mass spectrometer. During the trajectory to the cathode the drops are transformed into solvent-free cationic complexes, which are then analysed by the mass spectrometer. The spectrum of composite masses is then decomposed in the possible single complexes. 

Liquid introduction in atmospheric pressure chemical ionization resembles ionspray except that a heated capillary is used in place of the charged capillary. Figure 9.7. The combination of heat and gas flow desolvates the nebulized droplets producing fine particles of solvent and analyte molecules. The solvent molecules are then ionized by a corona discharge and the solvent ions formed ionize the analyte molecules by atmospheric pressure chemical ionization. 

Charged Capillary — the electric double layer in pores determines rejection, ions of same charge as membrane ate attracted and counter-ions are rejected due to the streaming potential,... 

FIGURE 5.3 Schematic representation of the electrical double layer at a negatively charged capillary wall. 

Lopez-Herrera, J. M., A. M. Ganan-Calvo A note on charged capillary jet breakup of conducting liquids experimental validation of a viscous one-dimensional model, J. Fluid Mech. 501, 303-326 (2004). 

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