Gradient shape parameter

Kig. 1.27. Examples of linear, concave and convex gradienis from 0 lo 10091 sironger eluent. B. in 20 min (at 1 ml/min) described by a gradient function (dependence of the concentration of B. on the volume of the cluate from the start of the gradient. V) with various values of the gradient shape parameter k. 

If the retention vs. composition relationships for the solutes i, i + 1 and j are known, then the gradient parameters A, B and k can readily be calculated for the optimum gradient according to equation 6.6. Not unexpectedly, the value of the shape parameter K turns out to be of little significance for an optimization procedure in which only three solutes affect the result [624]. Therefore, it may be sufficient to optimize the parameters A and B for a linear gradient (k— 1). 

The gradient system should be capable of producing a variety of gradient shapes. Linear gradients are common, but the Snyder solvent parameter produced will not likely be linear, as was shown earlier in Figure... 

Mobile phase parameters that have to be optimized include the salt type, concentration, gradient shape, pH, temperature, and possibly the addition of a surfactant or organic solvent [368-372]. The change in free energy on protein binding to the stationary phase is determined mainly by the contact surface area between the protein and stationary phase and by the salt type determined by its ability to increase the surface tension of aqueous solutions. Solvophobic theory predicts that in the absence of specific salt-protein interactions and at sufficient ionic strength the logarithm of the retention factor is linearly dependent on the surface tension of the mobile phase, which in turn, is a linear function of the salt concentration Eq. (4.13)... 

The chemistry of the lithographic process has not yet been fully elucidated. However, several parameters are expected to influence the final gradients, such as the precise structure and chemistry of the Ti02 layer, the humidity of the ambient air, and the size of the air gap between the substrate and the photocatalytic layer. Optimization of these parameters should allow better control of the final chemical gradient shape, slope, and resolution. 

The first attempt in this direction was made in 1991 [15]. Nuclei (embryos) were taken as spheroidal (ellipsoids of rotation) with a symmetry axis being directed along Vc, and the parameters J n (jj x) and Rj. (J x). In this case, AG is a function of two arguments, the volume V and the shape parameter, y = R /R at a fixed concentration gradient, Vc=l/L. We get... 

One important experimental parameter is also the furnace which is used in the thermogravimetric apparatus. There always exist pronounced radial and vertical temperature gradients which can be found by calibration runs. As an example, the determination of the vertical temperature distribution by Wiedemann41 may be referred to. Also the amount and shape of the sample can contribute to a temperature gradient. This fact is of special importance for kinetic studies. Considerable temperature differences - up to several °C - can exist at different locations of the sample holder. 

In addition, the use of fast gradients elution mode has become the bioanalytical mainstream as a possible way to improve peak parameters (shape and symmetry) and to minimize method development time, especially for the multi-analytes methods. 

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