Analyte velocity

There is not an analytical velocity function for the y-direction velocity at the flights, so the wide channel approximation is used for demonstration purposes with a pressure gradient of zero. Using the equation developed previously for screw rotation for a very wide shallow channel, the transformed Lagrangian form of is the same as the laboratory form for barrel rotation and is as follows ... 

The fluid that is confined between the parallel plates flows due to a drag flow caused by an upper plate velocity, uq, and a pressure flow caused by a pressure drop in the x-direction of Ap. The combined analytical velocity field is given by... 

Another way to reduce the fluorescence background, especially from plastic chips, is to modulate the velocity of a fluorescent analyte. The analyte velocity is modulated by periodic variation (in 7-20 Hz) of the separation voltage. Noise rejection is achieved using a lock-in amplifier because only the fluorescent signal but not the background from the chip substrate was modulated. With this method, a decrease in LOD by one order of magnitude has been obtained [685],... 

Wang, S., Morris, M.D., Plastic microchip electrophoresis with analyte velocity modulation. Application to fluorescence background rejection. Anal. Chem. 2000, 72, 1448-1452. 

Since DNA fragments from the PCR typically are contained in a high salt matrix, their mobility will vary depending on sample salt concentration. Thus, proper identification of these DNA fragments requires the use of an internal standard to normalize analyte velocity. This practice corrects for variance in fragment mobility due to sample matrix differences (i.e., salt content). These internal standards are included for size determination (in bp) as well as a reference for migration time. Candidates for such internal standards include the primer or primer-dimer peaks, since both components are already present in the PCR mixture alternatively, one or more coinjected standard DNA peak s may be chosen. If any of these fragments are to serve as the internal standard, they must be separated from one another and any PCR product, a precondition that is not easily met when the size of the PCR product is below 60 bp. 

Because of the success encountered by finite elements in the solution of elliptic problems, it was extended (in the 80s) to the advection or transport equation which is a hyperbolic equation with only one real characteristic. This equation can be solved naturally for an analytical velocity field by solving a time differential equation. It appeared important, when the velocity field was numerically obtained, to be able to solve simultaneously propagation and diffusion equations at low cost. By introducing upwinding in test functions or in the discretization scheme, the particular nature of the transport equation was considered. In this case, a particular direction is given at each point (the direction of the convecting flow) and boundary conditions are only considered on the part of the boundary where the flow is entrant. 

While there are a number of methods by which analytes can be stacked or preconcentrated in CE, ultimately, all stacking phenomena require a change in analyte velocity as the analyte transitions... 

Equation (4.13) suggests that the analyte does not migrate at all (n = 0) and when 0 = 1. It also suggests that the analyte moves with the same velocity as the mobile phase = v). The analyte velocity through the column equals the length, L, of the column divided by the analyte retention time, tgi... 

Using the separation of variables method, the analytical velocity components corresponding to the electroosmotic force are obtained as... 

Separation by electrophoresis is based on differences in analyte velocity in an applied electric field within the capillary. The electrophoretic mobility of the analyte (ji ) depends on the characteristics of the analyte (electrical charge, molecular size, and shape) and the characteristics of the running buffer (type and ionic strength of the electrolyte, pH, viscosity, and properties of the additives) in which the migration takes place [1-3]. 

I is the effective capillary length (the distance between the points of injection and detection) and Vj.p is the analyte velocity. 

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