Mobile phase selection, guidelines

Guidelines on mobile phase selection are discussed in Chapter 2, Section 2.3 and are illustrated in the case study below. After evaluation of the first sample chromatograms, further method development to fine-tune the separation will be performed until all method goals are achieved. Other bonded phases or column configurations can be selected to enhance method performance. These are discussed in the Section 8.6. 

Due to the fact that the primary structure of the Ultrahydrogel packing is a hydroxylated methacrylate, the interaction of many polar polymers with the packing is minimized easily. The presence of small amounts of anionic functions on the surface of the polymer usually requires the addition of salt to the mobile phase. A common mobile phase for many applications is 0.1 M NaN03. Detailed eluent selection guidelines are given in Table 11.6. 

The last two sections characterized the elements of a chromatographic system and discuss different separation tasks. This section provides guidelines to develop the chromatographic system for a given separation problem. The classical recommendation for preparative separations performed by elution chromatography is as follows Find a mobile phase with high solubility, a compatible stationary phase and then optimize selectivity, capacity and efficiency followed by a systematic increase in column load. 

Practically speaking, the mobile phase should not degrade the stationary phase, should have adequate solvency for the solute mixture, and should not interfere with product recovery in preparatory or commercial separations.f For guidelines on solvent selection for partition and adsorption LC, see Refs. f (For guidelines in ion chromatography see Weiss in Bibliography. )... 

Based on Snyder s solvent characterization (25), a new mobile phase optimization method, the PRISMA system (Figure 4) has been developed by Nyiredy et al. (53-58). The system consists of three parts In the first part, the basic parameters, such as the stationary phase, vapor phase and the individual solvents are selected by TLC. In the second part, the optimal combination of these selected solvents is selected by means of the PRISMA model. The third part of the system includes selection of the appropriate FFPC technique (OPLC or RPC) and HPTLC plates, selection of the development mode, and finally application of the optimized mobile phase in the various analytical and preparative chromatographic techniques. This system provides guidelines for method development in planar chromatography. The basic system for an automatic mobile phase optimization procedure, the correlation between the selectivity points for saturated TLC systems at a constant solvent strength (horizontal function), was described (59) by the function hRf= a(Pj) + (Fj) + c. 

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