Experimental Parameters that Affect Retention

The CFS hollow fiber suppressor (see Section 4.3.2) that was developed for cation-exchange chromatography could also be applied to cation analysis via ion-pair chromatography. It featured good solvent stability and sufficient permeability for the anionic ion-pair reagent This suppressor was regenerated with tetramethylammonium hydroxide at a concentration of c = 0.04 mol/L. 

The solvent stability of the CMMS micromembrane suppressor, introduced in Section 4.3.3, is sufficient to employ such suppressors in the ion-pair chromatography of cations. In this case, the suppressor is regenerated with tetrabutylam-mounium hydroxide. The regenerant concentration adheres to the concentration of the ion-pair reagent A reagent concentration of c = 2mmol/L, for example, requires a TBAOH concentration of c = 0.04 mol/L. 

The primary advantage of ion-pair chromatography over ion-exchange chromatography is its great flexibility, which allows the chromatographic conditions to be 

The effects on the retention process achieved by varying those individual parameters are discussed next. 

The following discusses the effects of varying individual parameters on the retention process. 

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Another source of deviations to the ideal behavior is the smoothness of the channel surface which, in reality, is hardly perfect. The surface quality affects substantially both retention and zone dispersion. Smith et al. [223] illustrated this fact experimentally for Th-FFF. Dilks et al. [458] studied experimentally the effect of sample injection and flow pattern on the zone shape inside the channel by performing measurements in a transparent channel and photographing the colored zones formed under various conditions of injection, flow, and geometric channel irregularities. One important result was that even apparently minor channel irregularities can give rise to considerable distortion of the zone formed. In Fl-FFF, the membrane is the critical parameter as ideally it has to fulfill the requirements of pressure and mechanical stability, even surface, uniform pore size, inert behavior with respect to solvent and samples and sufficient counter pressure to achieve smooth and uniform flow rates. A membrane fulfilling all the above requirements does not exist so that the choice of a membrane for Fl-FFF is always a compromise and depends on the analytical problem. In addition, for all other FFF techniques, the surface quality, in particular the smoothness of the channel accumulation wall, substantially affects both retention and zone dispersion. Smith et al. [223] illustrated this fact experimentally for Th-FFF. 

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