INDEX electrophoretic mobility

Electrophoretic mobilities of the quartz particles in cobalt (II) perchlorate solutions were determined with a calibrated Zeta-Meter apparatus. Coagulation sedimentation behavior was followed using a stop-flow type apparatus. The dispersion is pumped in a closed loop from an equilibration vessel through an optical cell located in the sample compartment of a recording spectrophotometer. From the optical densitytime curve obtained from the time the pump is switched off, the turbidity index (in arbitrary units) is obtained as the slope of the curve at zero time. 

Model particle mobility has been determinated with the Tiselius method (Tiselius, 1937, 1938). This method also allows the integration of the mobility of a large number of particles even if the refractive index is very close to that of the electrolyte medium, allowing to minimize the experimental errors inherent to the classical microelectrophoretic techniques. The electrophoretic mobilities will not be transformed into surface charges because the theoretical relationship between these parameters is highly dependant on the particle radius of curvature and the electrolyte concentration in the vicinity of the particle (Hunter and Wright, 1971). For both methods, the analytical error falls below 5 %, however, it increases up to 10 % for natural composite samples and/or low mobilities. 

The index of electrophoretic mobility as used in this article is defined in Section IV (p. 82). 

Finally, if heavy beads such as silica (SG = 2.1) are used, they can be assembled into a regular matrix by sedimentation [20]. One particular advantage of silica beads is that, after assembling them in a glass cell, sucrose can be added to the electrophoresis buffer to closely match the index of refraction of silica. This leads to a transparent material that is ideal for optical detection (at the expense of separation time, since sucrose increases the medium s viscosity, and thus reduces electrophoretic mobility). A second advantage is that some of the well-documented surface treatment strategies against electroosmosis developed for capillary electrophoresis can be directly transposed. 

Another handicap of the electrophoretic method concerns the difficulties in estimation of the components (5), first in terms of refractive index increments, then in terms of grams dried protein, and particularly in terms of grams protein nitrogen for comparison with the results of Kjeldahlization. Estimation of the refractive-index increment of a component in so complex a system as plasma necessitates a number of arbitrary assumptions and conventions which may introduce errors of considerable magnitude. The apparent mobility and refractive-index increment of a component, it is now clear, is determined not only by the properties, concentration, and environment of that one component, but is a function of the mobilities and concentrations of all components of the system. Environmental factors such as pH, ionic strength, type of ion, and total protein concentration play an important part in the resolution and distribution of the components and must be arbitrarily standardized. The labile mobilities of some a and j9 components, and interactions between lipides and/or carbohydrates and proteins (andjprobably between two or more proteins to form complexes) add further uncertainties, par-... 

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