Window diagrams binary mobile phases

Prus and Kowalska [75] dealt with the optimization of separation quality in adsorption TLC with binary mobile phases of alcohol and hydrocarbons. They used the window diagrams to show the relationships between separation selectivity a and the mobile phase eomposition (volume fraction Xj of 2-propanol) that were caleulated on the basis of equations derived using Soezewiriski and Kowalska approaehes for three solute pairs. At the same time, they eompared the efficiency of the three different approaehes for the optimization of separation selectivity in reversed-phase TLC systems, using RP-2 stationary phase and methanol and water as the binary mobile phase. The window diagrams were performed presenting plots of a vs. volume fraetion Xj derived from the retention models of Snyder, Schoen-makers, and Kowalska [76]. 

The constants a, b, and m in eqn [3] depend on the solute and on the chromatographic system. b = (ka) " , where ka is the retention factor in a pure nonpolar solvent. Equation [2] or [3] can be used as the basis of optimization of the composition of two-component (binary) mobile phases in NPLC, using a common window diagram or overlapping resolution mapping approach, as illustrated in an example in Figure 3. 

Single-parameter optimization employs several experiments at preselected values of the optimized parameter (such as the concentration of the strong solvent in a binary mobile phase, pH, temperature) to predict the resolution as a function of the optimized parameter using empirical or simple model-based calculations. Then, plots are constructed (the window diagrams ) in which the range of the optimized parameter is searched for the value that provides the desired resolution for all adjacent bands in the chromatogram in the shortest time. An example of a window diagram (Pig. 5) illustrates the approach adopted for the optimization of a binary mobile phase in NPLC. 

Otto and Wegscheider [562, 563] applied the window diagram method for the simultaneous optimization of the (binary methanol-water) mobile phase composition, the ionic strength and the pH for the separation of ionic solutes in RPLC. They fitted the experimental data to a semi-empirical 13-parameter equation based on eqn.(3.45) for the composition effect, eqn.(3.71) for the effect of the ionic strength and eqn.(3.70) for the... 

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